ω‐Conotoxin GVIA is a potent inhibitor of sympathetic neurogenic responses in rat small mesenteric arteries

Abstract

1We have investigated the effects of the N-type calcium channel blocker, co-conotoxin GVIA, on contractile responses to nerve stimulation, noradrenaline and KCI in rat small mesenteric arteries. In separate experiments, single and summated excitatory junctional potentials (ej.ps) evoked by nerve stimulation were recorded with an intracellular electrode in the absence and presence of co-conotoxin. 2 Electrical field stimulation of intramural sympathetic nerves (30 V; 0.25 ms pulse width; 3s train length; 4-24 Hz) caused frequency-dependent contractions. Cumulative concentration-response curves for the contractions induced by noradrenaline and KCI were constructed in the same preparations. Stimulation at 0.2 Hz and 10Hz induced respectively single ej.ps without contractions and summated ej.ps associated with a contractile response. 3 co-Conotoxin (0.1 to 3 nM) inhibited markedly and in a concentration-dependent manner both the contractions and ej.ps to electrical field stimulation. The concentration-response curves to exogenous noradrenaline and KCI remained unaffected. 4 The time-course for the effects of co-conotoxin (0.3 to 3 nM) indicated a slow onset of action with at least one hour to achieve an equilibrium. 5 The experiments indicate that co-conotoxin acts prejunctionally to inhibit sympathetic neurotransmission in rat small arteries presumably by inhibition of noradrenaline release. We suggest that w9-conotoxin could be a useful tool to study the control of vascular tone through the autonomic nervous system.

Vasodilatory Effect of Cilnidipine, an L-type and N-type Calcium Channel Blocker, on Rat Kidney Glomerular Arterioles

“…[10][11][12]18) The N-type calcium channel is involved in sympathetic neurotransmission, [14][15][16] and it was shown that cilnidipine suppresses the release of norepinephrine from sympathetic nerve terminals in perfused SHR mesentery specimens. It was shown that cilnidipine suppresses sympathetic nerve activity of SHRs as well as normotensive rats.…”

“…Several studies have shown that when norepinephrine (NE) is released from sympathetic nerve terminals there is an influx of extracellular calcium through calcium channels. [14][15][16] Norepinephrine constricts both the afferent and efferent arterioles. 17) It has been shown that cilnidipine suppresses NE release from the perfused vascular bed of SHR mesentery.…”

Facilitation of sympathetic neurotransmission by phosphatidylinositol-4,5-bisphosphate-dependent regulation of KCNQ channels in rat mesenteric arteries

“…The following drugs were used: bradykinin (10 À7 mol l À1 ), 3 U-73122 (10 À6 mol l À1 ), 20 U-73433 (10 À6 mol l À1 ), 20 cyclopiazonic acid (3 Â 10 À6 mol l À1 ), 21 HC-030031 (5 Â 10 À6 mol l À1 ), 22 H-89 (10 À6 mol l À1 ), 8,23 XE-991 (10 À5 mol l À1 ), 24 bisindolylmaleimide-I (10 À6 mol l À1 ), 25 capsaicin (10 À5 mol l À1 ), 26 capsazepine (5 Â 10 À6 mol l À1 ) 27 and phentolamine (10 À4 mol l À1 ) 28 from Sigma-Aldrich (St Louis, MO, USA) arachidonyl trifluoromethyl ketone (3 Â 10 À5 mol l À1 , AACOCF 3 ) 29 from Calbiochem (San Diego, CA, USA) o-conotoxin GVIA (2 Â 10 À9 or 10 À6 mol l À1 ) 30,31 and Calcitonin Gene-Related Peptide (Human, 8-37) (CGRP8-37, 10 À7 mol l À1 ) 32 from Peptide Institute (Osaka, Japan) and wortmannin (10 À5 mol l À1 ) 33 and AP-18 (10 À6 mol l À1 ) 34 from Biomol (Plymouth Meeting, PA, USA). Stock solutions of bradykinin, phentolamine, oconotoxin GVIA, H-89 and CGRP8-37 were dissolved in distilled water.…”

Effects of N‐, P‐ and Q‐type neuronal calcium channel antagonists on mammalian peripheral neurotransmission

“…h species but were more ef-N-type Ca2+ channels are dominant in controlling neurotransmitter release in most sympathetically-innervated preparations that have been examined. CTX GVIA has been shown to be a selective inhibitor of sympathetic neurotransmission in the rat mesenteric artery (Pruneau & Angus, 1990a) and, even at concentrations four orders of magnitude greater than required to block N type Ca2+ channels, does not affect post-junctional L-type channels or ax-adrenoceptors (Whorlow et al, 1996). Blockade of sympathetic neurogenic responses with CTX GVIA has been observed in isolated preparations of rabbit ear (De Luca et al, 1990;Zygmunt & H6gestatt, 1993) and pulmonary (Russell et al, 1990) artery, human saphenous vein (Fabi et al, 1993), rat tail artery (Clasbrummel et al, 1989) and canine splenic artery (Ren et al, 1994).…”

“…thus inhibit neurotransmitter release from nerve terminals by a pre-junctional action (Hirning et al, 1988;Brock et al, 1989;Pruneau & Angus, 1990a). CTX GVIA is highly selective for N-type channels and does not affect other neuronal Ca2" channels, nor post-junctional L-type Ca2+ channels, even at concentrations four orders of magnitude higher than that required to block noradrenaline and ATP release from sympathetic nerves (Whorlow et al, 1996).…”