Ca²⁺ dependency of the release of nitric oxide from non‐adrenergic non‐cholinergic nerves

Abstract

1 The role of Ca2" in nitrergic neurotransmission was studied in the canine ileocolonic junction. 2 The specific N-type voltage-sensitive Ca2" channel blocker w-conotoxin GVIA (CTX, 10-100 nM) significantly reduced the electrically-evoked (2-16 Hz, 1-2 ms pulse width) non-adrenergic noncholinergic (NANC) relaxations, preferentially affecting those to low frequency stimulation, in circular muscle strips of the ileocolonic junction. In contrast, the nerve-mediated NANC-relaxations in response to acetylcholine (30 JAM), y-aminobutyric acid (100IM) and adenosine 5'-triphosphate (100 I1M), as well as the relaxations to nitric oxide (NO) (3-10 IOM) and nitroglycerin (1 JAM), remained unaffected. 3 A NO-related substance (NO-R), released from the ileocolonic junction in response to NANC nerve stimulation (4 and 16 Hz, 2 ms pulse width), was assayed with a superfusion bioassay cascade. CTX (50 nM) reduced the release of NO-R induced by electrical impulses (4 Hz: from 18 ± 4% to 6 ± 4%; 16 Hz: from 33 ± 2% to 14 + 4%, n = 5), but not that in response to the nicotinic receptor agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP, 0.3 mM). In Ca2"-free medium, the release of NO-R evoked by electrical impulses or DMPP was inhibited. The L-type Ca2" channel blockers verapamil (1)(2)(3) and nifedipine (1 JM) had no effect.4 From these results we conclude that the release of NO-R in response to NANC nerve stimulation is Ca2"-dependent. The electrically-evoked release of NO-R results from Ca2" entry through CTX-sensitive N-type voltage-sensitive Ca2" channels, whereas that induced by nicotinic receptor activation involves CTX-insensitive Ca2" channels, different from the L-or N-type.

Presynaptic Muscarinic M2-Receptor-Mediated Inhibition of N-Type Ca2+Channels in Cultured Sphenopalatine Ganglion: Direct Evidence for Acetylcholine Inhibition of Cerebral Nitrergic Neurogenic Vasodilation

“…-Conotoxin, which is a selective blocker of neuronal N-type Ca 2ϩ channels, largely inhibits NO-mediated neurogenic vasodilation. This result suggests that Ca 2ϩ influx through the N-type Ca 2ϩ channels is important for activation of NOS, thereby leading to the synthesis and release of NO from the nitrergic nerves (Boeckxstaens et al, 1993(Boeckxstaens et al, , 1995. In the porcine basilar arteries, -conotoxin partially inhibited NO-mediated neurogenic vasodilation (Liu and Lee, 1999).…”

“…The release of neuronal NO and subsequent vasodilation have been shown to be Ca 2ϩ dependent (Boeckxstaens et al, 1993). -Conotoxin, which is a selective blocker of neuronal N-type Ca 2ϩ channels, largely inhibits NO-mediated neurogenic vasodilation.…”

“…rons (Boeckxstaens et al, 1993), suppression of these channels leads to a decreased NO formation and release from these nerves. Direct evidence for inhibition of voltage-dependent Ca 2ϩ channel by activation of muscarinic receptors in the cerebral perivascular nerves, however, has not been presented.…”

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

“…Ca 2ϩ together with calmodulin is required for nNOS activation . In the canine ileocolonic junction, -conotoxin GVIA, an N-type Ca 2ϩ channel inhibitor (McCleskey et al, 1987;Miller, 1987), or exposure of the tissue to Ca 2ϩ -free media reduced the inhibitory response to nitrergic nerve stimulation, whereas L-type Ca 2ϩ channel inhibitors nifedipine and verapamil were without effect (Boeckxstaens et al, 1993a). NO induced relaxation of rectal circular muscle with a concomitant decrease in intracellular Ca 2ϩ level (Takeuchi et al, 1998a).…”

“…Nicotine Kojima et al, 1993;McLaren et al, 1993;Mozhorkova et al, 1994), DMPP (Boeckxstaens et al, 1993a;Takeuchi et al, 1996), K ϩ , 5-HT (Boeckxstaens et al, 1990b;Bogers et al, 1991), ATP, and GABA (Boeckxstaens et al, 1991b) reportedly stimulate nitrergic nerves and release NO or a NO analog in the GI tract. Nerve action potentials appear to contribute to the inhibitory response to these chemical stimuli because the induced relaxation is susceptible to tetrodotoxin.…”