Calcium channel subtypes and exocytosis in chromaffin cells: a different view from the intact rat adrenal

Abstract

In the intact rat adrenal gland perfused with an oxygenated Krebs-bicarbonate solution at 37°C, the electrical field stimulation of splanchnic nerves (100 V, 0.5 ms duration, 10 Hz during 10 s) produced transient catecholamine release peaks that were reproduced in subsequent stimuli, applied at 8-min intervals. ω-Conotoxin GVIA (0.3 µM) caused only a modest inhibition of the secretory response, suggesting that the N-subtype of voltage-dependent Ca²⁺ channels are scarcely involved in such a response. Both ω-conotoxin MVIIC (1 µM) and furnidipine (1 µM) halved the secretion, suggesting that the L- and P/Q-types of Ca²⁺ channels were involved. N-type Ca²⁺ channels appear to be involved in the maintenance of secretion in response to sustained stimulus since ω-conotoxin GVIA (0.3 µM) reduced the catecholamine output to 28%. When secretion was elicited by acetylcholine (10 µM), furnidipine reduced the catecholamine release by 50% and ω-conotoxin MVIIC by 40%, whereas ω-conotoxin GVIA did not modify the response. The K⁺-induced secretory responses (23.6 mM K⁺, 15 s) were reduced 75% by furnidipine and 45% by ω-conotoxin MVIIC, indicating that this type of stimulation preferentially recruited L-type channels. These data show that electrical stimulation recruits Ca²⁺ channel subtypes different from those recruited by direct depolarization of chromaffin cells.