Myogenic nitric oxide synthase activity in canine lower oesophageal sphincter: morphological and functional evidence.
1. Studies on canine lower oesophageal sphincter (LOS) evaluated the existence and function of a myogenic, nitric oxide synthase (NOS) by use of immunocytochemistry for NOS isozymes, NADPH-d histochemistry, [3H]-L-arginine to [3H]-L-citrulline transformation. In addition, functional studies in the muscle bath were performed. 2. Smooth muscle bundles or freshly isolated smooth muscle cells of LOS were NADPH-d reactive but did not recognize some antibodies against neural, endothelial or inducible NOS. NADPH-d reactivity and immunoreactivity to a neural NOS antibody were colocalized in LOS enteric nerves. Muscle plasma membrane-enriched fractions from fresh and cultured LOS cells converted [3H]-L-arginine to [3H]-L-citrulline; activity was mostly Ca2+/calmodulin-dependent. 3. N-Nitro-L-arginine (L-NOARG) persistently increased tone (blocked by L-arginine) in muscle strips despite blockade of nerve function. Nifedipine prevented or abolished L-NOARG-induced, but not carbachol-induced, contraction showing that tone increase by L-NOARG required functional L-Ca channels. 4. Membrane-bound, myogenic NOS in canine LOS may release NO continuously when Ca2+ entry through L-Ca channels occurs under physiological conditions and thereby modulate tone in LOS.
Salapatek
A M
AM
Playfair Neurosciences Centre, The Toronto Hospital, ON, Canada.
Wang
Y F
YF
Mao
Y K
YK
Lam
A
A
Daniel
E E
EE
D000818:Animals; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004943:Esophagogastric Junction / Q000201:enzymology*; D005260:Female; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism*; D009252:NADPH Dehydrogenase / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019335:Nitroarginine / Q000494:pharmacology; D018408:Patch-Clamp Techniques
D004791:Enzyme Inhibitors; D019335:Nitroarginine; D019001:Nitric Oxide Synthase; D009252:NADPH Dehydrogenase