ω‐agatoxin IVA blocks nicotinic receptor channels in bovine chromaffin cells

Abstract

We have studied the contribution of P-type voltagedependent Ca 2+ channels to both catacholamine (CA) and ATP secretion from bovine chromaffin cells induced by high K ÷ or nicotine using ¢o-agatoxin IVA, a selective blocker of P-type voltage-dependent Ca 2÷ channels. We found that high K ÷ (75 raM) induced the release of about 13% of norepinephrine, 5% epinephrine and 11% ATP, and that ¢o-agatoxin (100 nM) did not affect this secretion. However, both nicotine-induced CA and ATP secretion were significantly blocked (about 50%) by ¢o-agatoxin IVA (100 nM). In addition, this toxin also reversibly blocked (about 70%) the inward current induced by nicotine in bovine chromaffin cells. The results suggest that, besides its known action of blocking P-type voltage-dependent channels, ¢o-agatoxin is a potent and reversible blocker of the nicotinic receptor channel in chromaffin cells, and that this action would explain the blockade of nicotine-induced secretion.

Tricyclic antidepressants block cholinergic nicotinic receptors and ATP secretion in bovine chromaffin cells

“…Recording of chromaffin cell nicotinic receptor‐activated currents under voltage‐clamp was done, using the nystatin‐perforated patch‐clamp technique, as previously described [14]. Chromaffin cells were bathed in a solution with the following ionic composition (in mmol/l): NaCl 140; KCl 5.9; MgSO 4 1.2; CaCl 2 2.5; HEPES 15 and glucose 11 (pH 7.4).…”

Calcium Signaling and Exocytosis in Adrenal Chromaffin Cells

“…Granja et al (180) showed that catecholamine secretion induced by high K ϩ is not affected by -agatoxin IVA (100 nM); nevertheless, when secretion was activated by nicotine, the -agatoxin significantly decreased catecholamine release by 50%. Thus Granja et al (180) conclude that -agatoxin IVA could also affect the nicotinic receptor.…”

“…Granja et al (180) showed that catecholamine secretion induced by high K ϩ is not affected by -agatoxin IVA (100 nM); nevertheless, when secretion was activated by nicotine, the -agatoxin significantly decreased catecholamine release by 50%. Thus Granja et al (180) conclude that -agatoxin IVA could also affect the nicotinic receptor. Duarte et al (129) show that FTX decreases K ϩ -evoked norepinephrine release to 25% and epinephrine release to 39% of the control levels; the combination of FTX plus nitrendipine further decreases norepinephrine and epinephrine release to 12 and 24% of the control levels.…”

Multiple calcium channels are required for pituitary adenylate cyclase-activating polypeptide-induced catecholamine secretion from bovine cultured adrenal chromaffin cells

“…Catecholamine secretion induced by K + depolarisation has been shown to be 20-50% dependent upon entry of calcium through L-type calcium channels (Lopez et al 1993(Lopez et al , 1994. K + -induced secretion from bovine chromaffin cells does not require entry of calcium through N- (Owen et al 1989) or P-type (Granja et al 1995) calcium channels but ω-conotoxin MVIIC reduces secretion by 50%. In preliminary experiments, we have found K + -induced secretion was reduced by nitrendipine, ω-agatoxin IVA and by ω-conotoxin MVIIC, but not by ω-conotoxin GVIA (O'Farrell and Marley, unpublished).…”

“…The contribution of different types of calcium channels to calcium-dependent secretion induced by nicotinic receptor agonists are inconclusive due to the ability of calcium channel antagonists to block the nicotinic receptor channel. Both dihydropyridines (Lopez et al 1993) and ω-agatoxin IVA (Granja et al 1995) have been shown to inhibit responses to nicotinic agonists without comparable effects on K + depolarisation, indicating that these antagonists may have an action in addition to blocking the voltage-sensitive channels.…”