Three types of Ca2+ channel trigger secretion with different efficacies in chromaffin cells.
To determine whether the different types of Ca2+ channels present in the same secretory cell contribute equally to secretion, we used chromaffin cells to analyse the coupling between three distinct types of Ca2+ channel and exocytosis. These are omega-conotoxin-GVIA-sensitive N-type channels, omega-agatoxin-IVA-sensitive P-type Ca2+ channels and dihydropyridine-sensitive facilitation Ca2+ channels, which are normally quiescent but are activated by depolarizing pre-pulses, repetitive depolarizations to physiological potentials, or agents that raise cyclic AMP. We have simultaneously monitored changes in capacitance as an assay of catecholamine secretion, and Ca2+ currents. Although all three types of Ca2+ channel trigger secretion individually, facilitation channels produce much greater secretion for a given size of Ca2+ current, indicating that they are coupled more efficiently to exocytosis. These results indicate that facilitation Ca2+ channels may be physically nearer vesicle release sites. They also show that low efficiency P- and N-type channels could trigger mild release and that high-efficiency facilitation channels may underlie the massive catecholamine release that occurs during the 'fight or flight' response.
Artalejo
C R
CR
Northwestern University, Department of Neurobiology and Physiology, Evanston, Illinois 60208.
Adams
M E
ME
Fox
A P
AP
D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D002838:Chromaffin System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005089:Exocytosis; D015737:Nisoldipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D013111:Spider Venoms / Q000494:pharmacology; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002395:Catecholamines; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D015737:Nisoldipine; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D020866:omega-Conotoxin GVIA; D002118:Calcium