Biochemistry and Molecular Biology Education, 2008
Cell signaling is an essential process in which a variety of external signals, defined as first m... more Cell signaling is an essential process in which a variety of external signals, defined as first messengers, are translated inside the cells into specific responses, which are mediated by a less numerous group of second messengers. The exchange of signals became a necessity when the transition from monocellular to pluricellular life brought with it the division of labor among the cells of the organisms: unicellular organisms do not depend on the mutual exchange of signals, as they essentially only compete with each other for nutrients. Calcium (Ca2+) was selected during evolution as second messenger, because its chemistry made it a much more flexible ligand than the other abundant cations in the primordial environment (Na+, K+, Mg2+). Ca2+ can accept binding sites of irregular geometries and is thus ideally suited to be a carrier of biological information. The Ca2+ signal has properties that set it apart from those of all other biological messengers: they will be reviewed in this contribution. Among them, the ambivalent character of the Ca2+ signal is the most important: while essential to the viability of the cells, it can also easily become a conveyor of doom.
Pflugers Archiv-european Journal of Physiology, 2003
Cyclic ADP-ribose (cADPr) is a second messenger that regulates intracellular free [Ca2+] ([Ca2+]i... more Cyclic ADP-ribose (cADPr) is a second messenger that regulates intracellular free [Ca2+] ([Ca2+]i) in a variety of cell types, including immature oocytes from the starfish Astropecten auranciacus. In this study, we employed confocal laser scanning microscopy and voltage clamp techniques to investigate the source of the cADPr-elicited Ca2+ wave originating from the cortical Ca2+ patches we have described previously. The Ca2+ swing was accompanied by a membrane current with a reversal potential of ≈+20 mV. Decreasing external Na+ almost abolished the current without affecting the Ca2+ response. Removal of extracellular Ca2+ altered neither the Ca2+ transient nor the ionic current, nor did the holding potential exert any effect on the Ca2+ wave. Both the Ca2+ response and the membrane current were abolished when BAPTA, ruthenium red or 8-NH2-cADPr were preinjected into the oocytes, while perfusion with ADPr did not elicit any [Ca2+]i increase or ionic current. However, elevating [Ca2+]i by uncaging Ca2+ from nitrophenyl- (NP-EGTA) or by photoliberating inositol 1,4,5-trisphosphate (InsP3) induced an ionic current with biophysical properties similar to that elicited by cADPr. These results suggest that cADPr activates a Ca2+ wave by releasing Ca2+ from intracellular ryanodine receptors and that the rise in [Ca2+]i triggers a non-selective monovalent cation current that does not seem to contribute to the global Ca2+ elevation.
Biochemistry and Molecular Biology Education, 2008
Cell signaling is an essential process in which a variety of external signals, defined as first m... more Cell signaling is an essential process in which a variety of external signals, defined as first messengers, are translated inside the cells into specific responses, which are mediated by a less numerous group of second messengers. The exchange of signals became a necessity when the transition from monocellular to pluricellular life brought with it the division of labor among the cells of the organisms: unicellular organisms do not depend on the mutual exchange of signals, as they essentially only compete with each other for nutrients. Calcium (Ca2+) was selected during evolution as second messenger, because its chemistry made it a much more flexible ligand than the other abundant cations in the primordial environment (Na+, K+, Mg2+). Ca2+ can accept binding sites of irregular geometries and is thus ideally suited to be a carrier of biological information. The Ca2+ signal has properties that set it apart from those of all other biological messengers: they will be reviewed in this contribution. Among them, the ambivalent character of the Ca2+ signal is the most important: while essential to the viability of the cells, it can also easily become a conveyor of doom.
Pflugers Archiv-european Journal of Physiology, 2003
Cyclic ADP-ribose (cADPr) is a second messenger that regulates intracellular free [Ca2+] ([Ca2+]i... more Cyclic ADP-ribose (cADPr) is a second messenger that regulates intracellular free [Ca2+] ([Ca2+]i) in a variety of cell types, including immature oocytes from the starfish Astropecten auranciacus. In this study, we employed confocal laser scanning microscopy and voltage clamp techniques to investigate the source of the cADPr-elicited Ca2+ wave originating from the cortical Ca2+ patches we have described previously. The Ca2+ swing was accompanied by a membrane current with a reversal potential of ≈+20 mV. Decreasing external Na+ almost abolished the current without affecting the Ca2+ response. Removal of extracellular Ca2+ altered neither the Ca2+ transient nor the ionic current, nor did the holding potential exert any effect on the Ca2+ wave. Both the Ca2+ response and the membrane current were abolished when BAPTA, ruthenium red or 8-NH2-cADPr were preinjected into the oocytes, while perfusion with ADPr did not elicit any [Ca2+]i increase or ionic current. However, elevating [Ca2+]i by uncaging Ca2+ from nitrophenyl- (NP-EGTA) or by photoliberating inositol 1,4,5-trisphosphate (InsP3) induced an ionic current with biophysical properties similar to that elicited by cADPr. These results suggest that cADPr activates a Ca2+ wave by releasing Ca2+ from intracellular ryanodine receptors and that the rise in [Ca2+]i triggers a non-selective monovalent cation current that does not seem to contribute to the global Ca2+ elevation.
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