DIFFERENT CONTRIBUTIONS OF L-TYPE AND Q-TYPE CA2+ CHANNELS TO CA2+ SIGNALS AND SECRETION IN CHROMAFFIN CELL SUBTYPES

In this study, we investigated the contribution of different subtypes of voltage-dependent Ca2+ channels to changes in cytosolic free Ca2+ ( [Ca2+](i)) and secretion in noradrenergic and adrenergic bovine chroma ffin cells. In single immunocytochemically identified chromaffin cells , [Ca2+](i) increased transiently during high K+ depolarization. Furni dipine and BAY K 8644, L-type Ca2+ channel blocker and activator. resp ectively, affected the [Ca2+](i) rise more in noradrenergic than in ad renergic cells. In contrast, the Q-type Ca2+ channel blocker omega-con otoxin MVIIC inhibited the [Ca2+](i) rise more in adrenergic cells. om ega-Agatoxin IVA (30 nM), which blocks P-type Ca2+ channels, had littl e effect on the [Ca2+](i) signal. The N-type Ca2+ channel blocker omeg a-conotoxin GVIA similarly inhibited the [Ca2+](i) rise in both cell t ypes. The effects of furnidipine, BAY K 8644, and omega-conotoxin MVII C on K+-evoked norepinephrine and epinephrine release paralleled those effects on [Ca2+](i) signals. However, omega-conotoxin GVIA and 30 nM omega-agatoxin IVA did not affect the secretion of either amine. The data suggest that, in the bovine adrenal medulla, the release of epine phrine and norepinephrine are preferentially controlled by Q and L-typ e Ca2+ channels, respectively. P- and N-type Ca2+ channels do not seem to control the secretion of either catecholamine.