CN1239713C - Application of ion channel inhibitor for curing arhythmia - Google Patents

Abstract

The invention discloses a mutant KCNQ1, namely S140G-KCNQ1. Also disclosed is a method for screening inhibitors of myocardial KCNQ1 potassium ion channels using KCNQ1, which includes the steps of: (a) transferring (i) an expression KCNQ1 expression vector and (ii) a KCNE1 expression vector or a KCNE2 expression vector into a mammalian cell; (b) adding the candidate substance to the culture medium of transformed mammalian cells, and measuring the electrophysiological potassium ion current before and after the addition, wherein a decrease in the electrophysiological potassium ion current after the addition of the candidate substance indicates that the substance is Inhibitor of the cardiac KCNQ1 potassium channel. This approach enables rapid screening of drug candidates for the treatment of atrial fibrillation.

Description

S140G mutant KCNQ1 protein and its application in screening ion channel inhibitors and enhancers

technical field

The invention relates to the field of molecular biology and medicine, more specifically the invention relates to the potentiating mutation of KCNQ1 gene in patients with familial atrial fibrillation and its application.

Background technique

According to the definition of the World Health Organization, atrial fibrillation (atrial fibrillation) is irregular and chaotic electrical activity in the atrium. Complete ventricular rate variability in the absence of high-grade or complete AV block.

Atrial fibrillation is one of the most common clinical arrhythmias, which can trigger heart failure or hemodynamic disorders, induce fatal arrhythmias such as ventricular tachycardia or ventricular fibrillation, lead to thrombosis and embolism events, and increase the mortality rate of underlying heart disease , Atrial fibrillation itself can also cause the heart to enlarge. According to statistics, the incidence of atrial fibrillation in the United States is 0.9%. With age, the incidence of atrial fibrillation increased sharply, as high as 5.9% in those over 65 years old. According to the Framinham study, one-third of strokes in the elderly (>65 years old) are caused by atrial fibrillation. Rates of atrial fibrillation were similar in Europe to the United States and slightly lower in Asia. Atrial fibrillation seriously endangers human health and brings considerable economic burden to the society.

As a special type of atrial fibrillation, idiopathic atrial fibrillation refers to the atrial fibrillation based on the heart lesion of the unknown bowl. Its nomenclature is confusing, and other names include isolated idiopathic atrial fibrillation, benign idiopathic atrial fibrillation, and familial idiopathic atrial fibrillation. Up to a third of cases of atrial fibrillation are classified as idiopathic (Lip GYH, Beevers DG (1995) ABC of atrial fibrillation: history, epidemiology, and importance of atrial fibrillation. BMJ 311:1361).

Atrial fibrillation (AF) is a common arrhythmia in humans, and its molecular pathogenic basis has not been well elucidated so far.

Contents of the invention

The purpose of the present invention is to provide a molecular pathogenic mechanism leading to atrial fibrillation. The mechanism is that a pathogenic mutation (S140G) occurs in the KCNQ1 gene, which leads to an increase in the ion flow of the myocardial potassium ion IKs ion channel.

Another object of the present invention is to provide a drug screening method based on the molecular pathogenic mechanism.

In a first aspect of the present invention, a method for screening inhibitors of myocardial KCNQ1 potassium ion channel is provided, comprising steps:

(a) Transforming the α subunit expression vector and the β subunit expression vector into mammalian cells to obtain transformed mammalian cells, wherein the α subunit expression vector is a KCNQ1 expression vector, and the β subunit expression vector is selected from the following group: KCNE1 expression vector or KCNE2 expression vector;

(b) adding the candidate substance to the culture medium of the transformed mammalian cell of step (a), and measuring the electrophysiological potassium ion current before and after adding the candidate substance,

Wherein, if the electrophysiological potassium ion current decreases after adding the candidate substance, it indicates that the active substance is an inhibitor of myocardial KCNQ1 potassium ion channel.

In a preferred example, the KCNQ1 expression vector expresses wild-type KCNQ1.

In another preferred example, the KCNQ1 expression vector expresses mutant KCNQ1. More preferably, the KCNQ1 expression vector expresses the S140G mutant KCNQ1.

In another preferred example, the β subunit expression vector expresses KCNE1.

In another preferred example, the β subunit expression vector expresses KCNE2.

In another preferred example, the determination method in step (b) is patch clamp method.

In a second aspect of the present invention, there is provided a method for screening a promoter of myocardial KCNQ1 potassium ion channel, comprising steps:

(a) Transforming the α subunit expression vector and the β subunit expression vector into mammalian cells to obtain transformed mammalian cells, wherein the α subunit expression vector is a KCNQ1 expression vector, and the β subunit expression vector is selected from the following group: KCNE1 expression vector or KCNE2 expression vector;

(b) adding the candidate substance to the culture medium of the transformed mammalian cell of step (a), and measuring the electrophysiological potassium ion current before and after adding the candidate substance,

Wherein, if the electrophysiological potassium ion current increases after adding the candidate substance, it indicates that the active substance is a promoter of myocardial KCNQ1 potassium ion channel.

In the third aspect of the present invention, a use of an S140G mutant KCNQ1 protein is provided, which is used for screening inhibitors or promoters of myocardial KCNQ1 potassium ion channels.

Description of drawings

Figure 1 shows that the ion current of the S140G-KCNQ1/KCNE1 ion channel is greatly increased compared with the ion current of the wild-type KCNQ1/KCNE1 ion channel.

Figure 2 shows that the ion current of the S140G-KCNQ1/KCNE2 ion channel is greatly increased compared with the ion current of the wild-type KCNQ1/KCNE2 ion channel.

Figure 3 shows the inhibitory effect of chromanol 293B on the S140G-KCNQ1/KCNE1 ion channel.

Figure 4 shows the inhibitory effect of chromanol 293B on the S140G-KCNQ1/KCNE2 ion channel.

Figure 5 shows the inhibitory effect of chromanol 293B on KCNQ1/KCNE2 ion channels.

Detailed ways

After extensive and in-depth research, the inventor conducted a genetic analysis on a patient with a Chinese hereditary atrial fibrillation family, located the pathogenic locus at 11p15.5 through genome-wide scanning, and found it in the KCNQ1 gene in this region A pathogenic mutation, S140G. The KCNQ1 gene encodes the α subunits of the cardiac potassium channel I _Ks (KCNQ1/KCNE1), KCNQ1/KCNE2, and KCNQ1/KCNE3 ion channels. This mutation exists in all patients and does not exist in normal people.

In order to elucidate the pathogenesis of this mutation, the inventors further conducted ion channel flow analysis of the mutant. Functional analysis showed that the S140G mutation enhanced the ion current of KCNQ1/KCNE1 and KCNQ1/KCNE2 ion channels. This is different from the previously discovered KCNQ1 mutations that cause LQT syndrome, which reduce the ion current of KCNQ1/KCNE1 and KCNQ1/KCNE2 ion channels.

Animal experiments and clinical research results show that most atrial fibrillation is caused by multiple reentry of atrial myoelectric conduction, and the shortening of action potential duration and effective refractory period is conducive to the formation of multiple reentry. The atrial fibrillation mutation S140G discovered by the present invention causes the enhancement of the function of the I _Ks ion channel (KCNQ1/KCNE1) and the KCNQ1/KCNE2 channel, and these enhancements can cause the duration of the atrial muscle action potential and the shortening of the effective refractory period, thereby causing atrial fibrillation .

Based on the above results, ion channel inhibitors targeting KCNQ1/KCNE2 ion flow may have a therapeutic effect on atrial fibrillation and other arrhythmias. Therefore, the present invention also provides a method for screening drug candidates for the treatment of atrial fibrillation, i.e. a method for screening the inhibitor of myocardial KCNQ1 potassium ion channel, which comprises steps:

(a) Transforming the α subunit expression vector and the β subunit expression vector into mammalian cells to obtain transformed mammalian cells, wherein the α subunit expression vector is a KCNQ1 expression vector, and the β subunit expression vector is selected from the following group: KCNE1 expression vector or KCNE2 expression vector;

(b) adding the candidate substance to the culture medium of the transformed mammalian cell of step (a), and measuring the electrophysiological potassium ion current before and after adding the candidate substance,

Wherein, if the electrophysiological potassium ion current decreases after adding the candidate substance, it indicates that the active substance is an inhibitor of myocardial KCNQ1 potassium ion channel.

As used herein, the term "wild-type KCNQ1" refers to the protein having the amino acid sequence shown in SEQ ID NO:1. KCNQ1 encodes the cardiac potassium I _Ks ion channel, the α subunit of KCNQ1/KCNE2 and KCNQ1/KCNE3 ion channels.

As used herein, the term "S140G-KCNQ1" refers to a protein having the amino acid sequence shown in SEQ ID NO: 2, and its corresponding coding sequence is shown in SEQ ID NO: 9. When S140G occurs, nucleotide 418 in SEQ ID NO: 9 changes from A to G, and amino acid 140 in SEQ ID NO: 2 changes from S to G. Functional analysis revealed that the S140G mutation increased the ion current of KCNQ1/KCNE2 and KCNQ1/KCNE3, which was in contrast to the ion current-decreasing effect of mutations previously found to cause LQT syndrome. Therefore, the S140G mutation may induce and maintain atrial fibrillation by shortening the action potential duration (Action Potential Duration, APD) and effective refractory period (Effective Refratory Period, ERP) of the atrial muscle.

As used herein, the term "KCNE1" refers to the protein encoded by the GenBank NM_000219 sequence, namely Potassium ( K ) C ha N nel Class E , Member 1.

As used herein, the term "KCNE2" refers to the protein encoded by the GenBank NM_005136 sequence, namely Potassium ( K ) C ha N nel Class E , Member 2.

As used herein, the term "KCNE3" refers to the protein encoded by the GenBank NM_005472 sequence, namely Potassium ( K ) C ha N nel Class E , Member 3.

Cells that can be used in the screening method of the present invention are not particularly limited. Representative examples include: mammalian cells, such as COS-7 cells, CHO cells, or oocytes of the vertebrate Xenopus.

The ion current measurement technique that can be used in the screening method of the present invention is not particularly limited. Representative examples include: patch clamp (for mammalian cells), or micro bielectrode clamp (for Xenopus oocytes).

The main advantage of the present invention is that it can effectively screen a large number of candidate drugs for the treatment of atrial fibrillation.

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental method that does not indicate specific conditions in the following examples is usually according to conventional conditions, such as Sambrook et al., molecular cloning: the conditions described in the laboratory manual (New York: Cold Spring Harbor Laboratory Press, 1989), or according to the conditions described in the manufacture conditions recommended by the manufacturer.

Example 1: Preparation of wild-type KCNQ1 expression vector

From the human kidney cDNA library (Clontech Inc.), positive clones were screened with isotope ³² P-labeled KCNQ1 DNA probe (PCR fragment). The resulting positive clones were directly sequenced and confirmed to be identical to the standard published sequence (Accession No.AF000571) in GenBank and had a complete coding sequence.

A primer is designed before the cDNA sequence ATG initiator, and has the ECoRI cutting point sequence (primer F: 5'-tc gag aat tcc tea cca tgg ccg cgg cct cct c (SEQ ID NO: 3)), at the terminator A primer was designed after TGA with an XbaI cutting point (primer R: 5'-ggt cga ctc tag acc cca tcc cct cct cagg (SEQ ID NO: 4)).

Using the primer pair (F, R), the human kidney cDNA library (Clontech Inc.) was used as a template for PCR amplification (HotStarTaq kit, Qiagen Company), and the resulting PCR product was purified by QIAquick PCR Purification Kit (Qiagen Company).

After the purified PCR product was digested with EcoRI and XbaI, it was ligated with the pCI vector (Promega Inc.) treated with the same enzyme, transferred into XL1-Blue competent cells, inoculated and cultured on ampicillin LB plate, picked Drug-resistant clones were sequenced to confirm the correctness of the clones.

As a result, the expression vector pCI-KCNQ1 inserted with the coding sequence of wild-type KCNQ1 was obtained.

Example 2: Preparation of mutant S140G-KCNQ1 expression vector

In this example, using the wild-type KCNQ1 expression plasmid prepared in Example 1 as a template, the site-directed mutagenesis technique (Site-directed Mutagenesis) was used to change the coding subsequence at the 140th position of the coding, and the coding Serine (serine) was changed to into the coding Glycin (glycine), made S140G mutant expression plasmid. The specific process is as follows:

Design and synthesize two pairs of PCR amplification primers. The first pair of primers (composed of forward primer 1 and reverse primer 1 containing the S140G mutation site) are used to amplify the product containing the fragment from the ECoRI cut point to the S140G mutation site is

5'-get agc ctc gag aat tcc tca c (SEQ ID NO: 5)

5'-gga cag cac gcc gaa gat g (SEQ ID N0:6)

The second pair of primers (composed of forward primer 2 and reverse primer 2 containing the S140G mutation site) are used to amplify the fragment from the S140G mutation site to the XbaI cut point, and the sequence is as follows:

5'-cat ctt cgg cgtgct gtc c (SEQ ID NO: 7)

5'-ggt cga ctc tag acc cea tcc (SEQ ID N0:8)

The primer sequence containing the S140G mutation site introduces the corresponding mutant nucleotide at the mutation site. Using the expression vector pCI-KCNQ1 prepared in Example 1 as a template, PCR amplification was performed with the first pair of primers (SEQ ID NO: 5 and 6) and the second pair of primers (SEQ ID NO: 7 and 8), respectively. The two fragments amplified by PCR were mixed, and the complete coding fragment was amplified with forward primer 1 and reverse primer 2 (SEQ ID NO: 5 and 8). The resulting PCR product was purified by QIAquick PCR Purification Kit (Qiagen Inc). After the purified PCR product was digested with EcoRI and XbaI, it was connected to the pCI vector (Promega Inc.) treated with the same enzyme, transferred into XL1-Blue competent cells, inoculated and cultured on the ampicillin LB plate, and the anti- Pharmacological cloning, sequencing confirmed the correctness of the cloning.

As a result, the expression vector pCI-S140G-KCNQ1 inserted with the mutant KCNQ1 coding sequence was obtained.

Example 3: The S140G mutation of KCNQ1 leads to enhanced KCNQ1/KCNE1 ion current

The S140G-KCNQ1 expression vector pCI-S140G-KCNQ1 prepared in Examples 1 and 2 and the wild-type KCNE1 expression plasmid (pIRES-KCNE1-CD8) were transformed into mammalian cells COS-7 cells. In another control experiment, the wild-type KCNQ1 expression vector pCI-KCNQI and the KCNE1 expression plasmid were transformed into mammalian cells COS-7 cells. Approximately 48 hours after cell transfection, electrophysiological potassium current measurements (using the patch clamp technique) were performed. Methods as below:

In a humidified environment containing 5% CO ₂ , COS-7 cells were cultured in Dulbecco's modified Eagle medium (supplemented ingredients: 10% fetal bovine serum, 100U/mL streptomycin, 100U/mL penicillin). Cells were transfected by the DEAE-Dextran precipitation method. With 0.75 μg of pCI-KCNQ1 or pCI-S140G-KCNQ1 plasmid DNA, 0.25 μg of pIRES-KCNEI-CD8 plasmid DNA (this plasmid is inserted in the pIRES vector (Clontech Inc.) respectively encoding KCNE1 gene and encoding CD8 gene Plasmids formed by two fragments). Transfect a plate of 35mm cells. Transfected COS-7 cells were identified with anti-CD8 antibody. Ion current recordings were performed at room temperature (~22°C) using Whole-Cell recording mode (VP500 Amplifier, BioLogic Inc). The inner solution of the electrode contains (mM): 150mM KCl, 0.5mM MgCl ₂ , 5mM EDTA, and 10mM HEPES, pH7.3. The water bath contains (mM): 150 mM NaCl, 5 mM KCl, 2 mM CaCl ₂ , 1 mM MgCl ₂ and 10 mM HEPES, pH 7.3. Electrode resistance 2.5-5MΩ. Membrane currents were induced by depolarization (membrane depolarization from -130 mV to +50 mV, holding voltage -80 mV).

The results are shown in Figure 1, the ion current of the S140G-KCNQ1/KCNE1 ion channel is greatly increased compared with the ion current of the wild-type KCNQ1/KCNE1 ion channel.

Example 4: The S140G mutation of KCNQ1 leads to enhanced KCNQ1/KCNE2 ion current

According to the same method as in Example 3, the S140G-KCNQ1 expression vector and the KCNE2 expression plasmid (pIRES-KCNE2-CD8) were transformed into appropriate mammalian cells COS-7 cells. In another control experiment, the expression vector of wild-type KCNQ1 and the expression plasmid of KCNE2 were transformed into appropriate mammalian cells COS-7 cells. Approximately 48 hours after cell transfection, electrophysiological potassium current measurements (using the patch clamp technique) were performed.

The results are shown in Figure 2, the ion current of the S140G-KCNQ1/KCNE2 ion channel is greatly increased compared with the ion current of the wild-type KCNQ1/KCNE2 ion channel.

Example 5: Screening of mutant S140G-KCNQ1/KCNE1 (I _Ks ) ion channel inhibitors

In this example, the S140G-KCNQ1 expression vector (pCI-S140G-KCNQ1) and the KCNE1 expression plasmid were transformed into suitable mammalian cells (such as COS-7 cells), and about 48 hours after the cells were transfected, the Electrophysiological Potassium Current Assay. By comparing whether the ion current intensity and characteristics have changed before and after adding the candidate inhibitor, it can be judged whether the compound has an inhibitory effect on the S140G-KCNQ1/KCNE1 ion channel. In addition, this method can also be used to compare the relative inhibitory effect of different inhibitors.

Repeat the process of Example 3, except that the candidate substance is added, chromanol 293B (Chromanol293B) (chemical name is trans-6-cyano4-{N-ethylsulfonyl-N-methylamino}-3-hydroxy-2,2- dimethyl-chromanane). It was found that the ion flow was completely suppressed (Fig. 3). Thus, chromanol 293B is an inhibitor of cardiac potassium channel I _Ks (KCNQ1/KCNE1).

Example 6: Screening of Mutant S140G KCNQ1/KCNE2 Ion Channel Inhibitors

In this example, the S140G-KCNQ1 expression vector (pCI-S140G-KCNQ1) and the KCNE2 expression plasmid were transformed into suitable mammalian cells (such as COS-7 cells), and about 48 hours after the cells were transfected, the Electrophysiological Potassium Current Assay. By comparing whether the ion current intensity and characteristics have changed before and after adding the candidate inhibitor, it can be judged whether the compound has an inhibitory effect on the S140G-KCNQ1/KCNE2 ion channel. In addition, this method can also be used to compare the relative inhibitory effect of different inhibitors.

Repeat the process of Example 4, the difference is that the candidate substance is added, Chromanol 293B (Chromanol293B) (chemical name is trans-6-cyano4-{N-ethylsulfonyl-N-methylamino}-3-hydroxy-2,2- dimethyl-chromanane). It was found that the ion flow was completely suppressed (Fig. 4). Thus, chromanol 293B is an inhibitor of cardiac potassium channels KCNQ1/KCNE2.

Example 7: Screening of wild-type KCNQ1/KCNE2 ion channel inhibitors

In this example, the wild-type KCNQ1 expression vector (pCI-KCNQ1) and the KCNE2 expression plasmid were transformed into suitable mammalian cells (such as COS-7 cells), and electroporation was performed about 48 hours after cell transfection. Physiological Potassium Current Determination. By comparing whether the ion current intensity and characteristics have changed before and after adding the candidate inhibitor, it can be judged whether the compound has KCNQ1/KCNE2 ion channel inhibitory effect. In addition, this method can also be used to compare the relative inhibitory effect of different inhibitors.

Repeat the process of Example 4, the difference is that the candidate substance is added, Chromanol 293B (Chromanol293B) (chemical name is trans-6-cyano4-{N-ethylsulfonyl-N-methylamino}-3-hydroxy-2,2- dimethyl-chromanane). It was found that the ion flow was completely suppressed (Fig. 5). Thus, chromanol 293B is an inhibitor of cardiac potassium channels KCNQ1/KCNE2.

All documents mentioned in this application are incorporated by reference in this application as if each were individually incorporated by reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Sequence Listing

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atggccgcgg cctcctcccc gcccagggcc gaaaggaagc gctggggttg gggccgcctg 60

ccaggcgccc ggcggggcag cgcgggcctg gccaaaaaat gccccttctc gctggaactg 120

gcggagggcg gcccggcggg cggcgcgctc tacgcgccca tcgcgcccgg cgccccaggt 180

cccgcgcccc atgtgtcccc ggccgcgccc gccgcgcccc cagttgcttc cgaccttggc 240

ccgcggccgc cggtgagcct agacccgcgc gtctccatat acagcacgcg ccgcccggtg 300

ttggcgcgaa cccacgtcca gggccgcgtc tacaacttcc tcgagcgtcc caccggctgg 360

aaatgcttcg tttaccactt cgccgtcttc ctcatcgtcc tggtctgcct catcttcagc 420

gtgctgtcca ccatcgagca gtatgccgcc ctggccacgg ggactctctt ctggatggag 480

atcgtgctgg tggtgttctt csggacggag tacgtggtcc gcctctggtc cgccggctgc 540

cgcagcaagt acgtggggcct ctgggggcgg ctgcgctttg cccggaagcc catttccatc 600

atcgacctca tcgtggtcgt ggcctccatg gtggtcctct gcgtgggctc caaggggcag 660

gtgtttgcca cgtcggccat caggggcatc cgcttcctgc agatcctgag gatgctacac 720

gtcgaccgcc agggaggcac ctggaggctc ctgggctccg tggtcttcat ccaccgccag 780

gagctgataa ccaccctgta catcggcttc ctgggcctca tcttctcctc gtactttgtg 840

tacctggctg agaaggacgc ggtgaacgag tcaggccgcg tggagttcgg cagctacgca 900

gatgcgctgt ggtggggggt ggtcacagtc accaccatcg gctatgggga caaggtgccc 960

cagacgtggg tcgggaagac catcgcctcc tgcttctctg tctttgccat ctccttcttt 1020

gcgctcccag cggggattct tggctcgggg tttgccctga aggtgcagca gaagcagagg 1080

cagaagcact tcaaccggca gatcccggcg gcagcctcac tcattcagac cgcatggagg 1140

tgctatgctg ccgagaaccc cgactcctcc acctggaaga tctacatccg gaaggccccc 1200

cggagccaca ctctgctgtc accccagcccc aaacccaaga agtctgtggt ggtaaagaaa 1260

aaaaagttca agctggaca aagacaatggg gtgactcctg gagagaagat gctcacagtc 1320

ccccatatca cgtgcgaccc cccagaagag cggcggctgg accacttctc tgtcgacggc 1380

tatgacagtt ctgtaaggaa gagcccaaca ctgctggaag tgagcatgcc ccatttcatg 1440

agaaccaaca gcttcgccga ggacctggac ctggaagggg agactctgct gacacccatc 1500

acccacatct cacagctgcg ggaacaccat cgggccacca ttaaggtcat tcgacgcatg 1560

cagtactttg tggccaagaa gaaattccag caagcgcgga agccttacga tgtgcgggac 1620

gtcattgagc agtactcgca gggccacctc aacctcatgg tgcgcatcaa ggagctgcag 1680

aggaggctgg accagtccat tgggaagccc tcactgttca tctccgtctc agaaaagagc l740

aaggatcgcg gcagcaacac gatcggcgcc cgcctgaacc gagtagaaga caaggtgacg 1800

cagctggacc agaggctggc actcatcacc gacatgcttc accagctgct ctccttgcac 1860

ggtggcagca cccccggcag cggcggcccc cccagagagg gcggggccca catcacccag 1920

ccctgcggca gtggcggctc cgtcgaccct gagctcttcc tgcccagcaa caccctgccc 1980

acctacgagc agctgaccgt gcccaggagg ggccccgatg agggggtcctg a 2031

Claims (9)

1. a method for screening the inhibitor of myocardial KCNQ1 potassium ion channel, is characterized in that, comprises steps: (a) Transforming the α subunit expression vector and the β subunit expression vector into mammalian cells to obtain transformed mammalian cells, wherein the α subunit expression vector is a KCNQ1 expression vector, and the KCNQ1 expression vector expresses the S140G mutant KCNQ1, and the β subunit expression vector is selected from the following group: KCNE1 expression vector or KCNE2 expression vector; (b) adding the candidate substance to the culture medium of the transformed mammalian cell of step (a), and measuring the electrophysiological potassium ion current before and after adding the candidate substance, Wherein, if the electrophysiological potassium ion current decreases after adding the candidate substance, it indicates that the active substance is an inhibitor of myocardial KCNQ1 potassium ion channel. 2. The method according to claim 1, wherein the mammalian cells are COS7 cells, CHO cells or oocytes of Xenopus laevis. 3. The method according to claim 1, characterized in that, the β subunit expression vector expresses KCNE1. 4. The method according to claim 1, characterized in that, the β subunit expression vector expresses KCNE2. 5. The method according to claim 1, characterized in that, the assay method in step (b) is patch clamp method. 6. A method for screening a promoter of myocardial KCNQ1 potassium ion channel, characterized in that, comprising the steps: (a) Transforming the α subunit expression vector and the β subunit expression vector into mammalian cells to obtain transformed mammalian cells, wherein the α subunit expression vector is a KCNQ1 expression vector, and the KCNQ1 expression vector expresses the S140G mutant KCNQ1, and the β subunit expression vector is selected from the following group: KCNE1 expression vector or KCNE2 expression vector; (b) adding the candidate substance to the culture medium of the transformed mammalian cell of step (a), and measuring the electrophysiological potassium ion current before and after adding the candidate substance, Wherein, if the electrophysiological potassium ion current increases after adding the candidate substance, it indicates that the active substance is a promoter of myocardial KCNQ1 potassium ion channel. 7. The use of an S140G mutant KCNQ1 protein, characterized in that it is used for screening inhibitors or promoters of myocardial KCNQ1 potassium ion channels. 8. The use according to claim 7, wherein the S140G mutant KCNQ1 protein has the amino acid sequence shown in SEQ ID NO:2. 9. A S140G mutant KCNQ1 protein, characterized in that its amino acid sequence is as shown in SEQ ID NO::2.

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