Ca2+ dependency of the release of nitric oxide from non-adrenergic non-cholinergic nerves.
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 omega-conotoxin GVIA (CTX, 10-100 nM) significantly reduced the electrically-evoked (2-16 Hz, 1-2 ms pulse width) non-adrenergic non-cholinergic (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 microM), gamma-aminobutyric acid (100 microM) and adenosine 5'-triphosphate (100 microM), as well as the relaxations to nitric oxide (NO) (3-10 microM) and nitroglycerin (1 microM), 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 Ca(2+)-free medium, the release of NO-R evoked by electrical impulses or DMPP was inhibited. The L-type Ca2+ channel blockers verapamil (1-3 microM) and nifedipine (1 microM) had no effect. 4. From these results we conclude that the release of NO-R in response to NANC nerve stimulation is Ca(2+)-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.
Boeckxstaens
G E
GE
Division of Gastroenterology, Faculty of Medicine, University of Antwerp, Antwerp-Wilrijk, Belgium.
De Man
J G
JG
Pelckmans
P A
PA
Cromheeke
K M
KM
Herman
A G
AG
Van Maercke
Y M
YM
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004285:Dogs; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000294:innervation; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D011817:Rabbits; D014700:Verapamil / Q000494:pharmacology; D020866:omega-Conotoxin GVIA
D018377:Neurotransmitter Agents; D010455:Peptides; D009569:Nitric Oxide; D020866:omega-Conotoxin GVIA; D014700:Verapamil; D009543:Nifedipine; D002118:Calcium