Abstract
The present study was designed to investigate whether nitric oxide (NO) could interfere with intracellular Ca++ release through different pathways in vascular smooth muscle. Phasic contractions of rat aorta induced by phenylephrine or caffeine in Ca++-free solution were used as an indicator of intracellular Ca++release through the inositol 1,4,5-triphosphate receptor pathway and the ryanodine receptor pathway, respectively. In addition, cytoplasmic Ca++ concentration ([Ca++]i) in vascular smooth muscle cells was determined by fluorescence measurement. Acetylcholine (ACh) inhibited the phenylephrine-evoked phasic contractions in Ca++-free solution in endothelium-intact but not -denuded aortic rings in a dose-dependent manner. However, ACh did not affect the action of caffeine. The inhibition by ACh was blocked completely by the NO synthase inhibitor Nω-nitro-l-arginine, which could be reversed totally by l-arginine but not d-arginine. Methylene blue, a soluble guanylate cyclase inhibitor, also abolished the inhibition by ACh. Sodium nitroprusside, an NO donor, attenuated the phenylephrine- but not caffeine-induced phasic contractions in denuded aortic rings in Ca++-free solution. The effect of sodium nitroprusside was reversed substantially by methylene blue. Furthermore, sodium nitroprusside inhibited the elevation of [Ca++]i induced by phenylephrine in vascular smooth muscle cells isolated from rat aorta in the absence of extracellular Ca++, which could be abolished significantly by methylene blue. These results suggest that NO selectively inhibits intracellular Ca++ release stimulated by inositol 1,4,5-triphosphate, but not caffeine in vascular smooth muscle.
Footnotes
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Send reprint requests to: Dr. Christina G. Benishin, Associate Professor, Department of Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
- Abbreviations:
- NO
- nitric oxide
- ACh
- acetylcholine
- SNP
- sodium nitroprusside
- cyclic GMP
- guanosine 3′,5′-cyclic monophosphate
- EGTA
- ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- l-NNA
- Nω-nitro-l-arginine
- ER
- endoplasmic reticulum
- IP3
- inositol 1,4,5-triphosphate
- fura-2/AM
- fura-2 acetoxymethyl ester
- HEPES
- N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid
- Received July 21, 1997.
- Accepted December 5, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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