Ca2+ regulation in the presynaptic terminals of goldfish retinal bipolar cells

J Physiol. 1995 Feb 15;483 ( Pt 1)(Pt 1):79-94. doi: 10.1113/jphysiol.1995.sp020569.

Abstract

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caffeine / pharmacology
  • Calcium / metabolism*
  • Calcium / pharmacology
  • Calcium Channels / metabolism
  • Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / pharmacology
  • Cell Membrane / metabolism
  • Cobalt / pharmacology
  • Goldfish / metabolism
  • Hydrogen-Ion Concentration
  • Membrane Potentials / physiology
  • Patch-Clamp Techniques
  • Presynaptic Terminals / metabolism*
  • Retina / cytology
  • Retina / physiology*
  • Ruthenium Red / pharmacology
  • Ryanodine / pharmacology
  • Sodium / pharmacology
  • Terpenes / pharmacology
  • Thapsigargin
  • Vanadates / pharmacology

Substances

  • Calcium Channels
  • Terpenes
  • Ruthenium Red
  • Ryanodine
  • Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone
  • Cobalt
  • Caffeine
  • Vanadates
  • Thapsigargin
  • Sodium
  • Calcium