Ca2+ regulation in the presynaptic terminals of goldfish retinal bipolar cells.
1. To investigate regulation of the intracellular free Ca2+ concentration ([Ca2+]i) in presynaptic terminals, the Ca2+ current (ICa) and [Ca2+]i in axon terminals were simultaneously monitored in acutely dissociated retinal bipolar cells under whole-cell voltage clamp. 2. The recovery phase of the Ca2+ transient, which was evoked by activation of ICa, became slower when the Na(+)-Ca2+ exchanger was suppressed by removing extracellular Na+. 3. Inhibition of the plasma membrane Ca2+ pump produced by raising extracellular pH to 8.4 increased the basal [Ca2+]i and caused incomplete recovery from the Ca2+ transient. These effects were not observed in orthovanadate-loaded bipolar cells. 4. The Ca2+ transient was not significantly affected by ryanodine, caffeine, thapsigargin, Ruthenium Red or FCCP. Internal Ca2+ stores may not participate in shaping the Ca2+ transient. 5. The ratio of the peak amplitude of the Ca2+ transient to the total amount of Ca2+ influx became smaller as the size of the Ca2+ influx increased. This action was not affected by blockage of Ca2+ transporters in the plasma membrane, or by reduction of the rate of Ca2+ influx. The peak amplitude of the Ca2+ transient seemed to be determined by Ca2+ buffering substances with a positive co-operativity.
Kobayashi
K
K
Department of Psychology, Faculty of Letters, University of Tokyo, Japan.
Tachibana
M
M
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology; D006054:Goldfish / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000502:physiology*; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014638:Vanadates / Q000494:pharmacology
D015220:Calcium Channels; D013729:Terpenes; D012430:Ruthenium Red; D012433:Ryanodine; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D003035:Cobalt; D002110:Caffeine; D014638:Vanadates; D019284:Thapsigargin; D012964:Sodium; D002118:Calcium