Extracellular calcium has distinct effects on fast and slow components of the depolarization-induced secretory response from chromaffin cells.
An increase in extracellular Ca2+ concentration from 0.25 to 10 mM enhanced secretion of norepinephrine and epinephrine induced by a high extracellular K+ concentration (75 mM). The increment in extracellular Ca2+ concentration also increased the observed peak inward Ca2+ current in response to long (10-s) depolarizing pulses from a holding potential of -55 mV to +5 mV, from about -26 to -400 pA. However, the total amount of Ca2+ influx into the cell only increased when the extracellular Ca2+ concentration was raised from 0.25 to 1 mM and then remained constant up to 10 mM extracellular Ca2+. ATP is cosecreted with catecholamines following a depolarizing stimulus. Kinetic studies indicated that ATP secretion had two components with time constants, in the presence of 2.5 mM extracellular Ca2+, of approximately 4 and 41 s, being the fast component of secretion produced by the exocytosis of approximately 220 chromaffin granules. The results suggest that, for a given depolarizing stimulus, the size and rate of release for the fast and slow components of secretion are dependent on extracellular Ca2+ concentration.
Granja
R
R
Departamento de Farmacología, Universidad de Alicante, Spain.
Izaguirre
V
V
Calvo
S
S
González-García
C
C
Ceña
V
V
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology; D002417:Cattle; D002478:Cells, Cultured / Q000378:metabolism / Q000502:physiology; D002838:Chromaffin System / Q000166:cytology* / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology
D015220:Calcium Channels; D000255:Adenosine Triphosphate; D002118:Calcium