Phase-dependent contributions from Ca2+ entry and Ca2+ release to caffeine-induced [Ca2+]i oscillations in bullfrog sympathetic neurons.
Sympathetic neurons display robust [Ca2+]i oscillations in response to caffeine and mild depolarization. Oscillations occur at constant membrane potential, ruling out voltage-dependent changes in plasma membrane conductance. They are terminated by ryanodine, implicating Ca(2+)-induced Ca2+ release. Ca2+ entry is necessary for sustained oscillatory activity, but its importance varies within the oscillatory cycle: the slow interspike rise in [Ca2+]i requires Ca2+ entry, but the rapid upstroke does not, indicating that it reflects internal Ca2+ release. Sudden alterations in [Ca2+]o, [K+]o, or [caffeine]o produce immediate changes in d[Ca2+]i/dt and provide information about the relative rates of surface membrane Ca2+ transport as well as uptake and release by internal stores. Based on our results, [Ca2+]i oscillations can be explained in terms of coordinated changes in Ca2+ fluxes across surface and store membranes.
Friel
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DD
Department of Molecular and Cellular Physiology, Stanford University School of Medicine, California 94305-5426.
Tsien
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RW
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D003470:Culture Media; D008564:Membrane Potentials; D009474:Neurons / Q000378:metabolism* / Q000502:physiology; D009994:Osmolar Concentration; D011892:Rana catesbeiana; D012433:Ryanodine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000166:cytology / Q000378:metabolism*
D002121:Calcium Channel Blockers; D003470:Culture Media; D012433:Ryanodine; D002110:Caffeine; D002118:Calcium