Abstract
Effects of sodium nitroprusside (SNP) on tension and cytosolic Ca 2+ concentration ([Ca 2+] i) in guinea-pig tracheal muscle were investigated by performing simultaneous tension/fura-2 signal measurement. Muscle tone was generated by exogeneous PGE 2 in the presence of indomethacin and atropine. As observed in terbutaline-induced relaxation, SNP-induced relaxation was not significantly affected by the presence of verapamil and it was accompanied by a correlative decrease in [Ca 2+] i. Exposed to cyclopiazonic acid, the relaxation and decrease in the fura-2 signal produced by SNP were attenuated in comparison with the responses to terbutaline. Further, relaxation produced by several cGMP-related agents was compared with that produced by several cAMP-related agents with regard to effects of CPA. In conclusion, lowering of [Ca 2+] i seems to be the most essential factor for SNP-induced, as well as for terbutaline-induced, relaxation, and Ca 2+ sequestration into the sacroplasmic reticulum is greatly responsible for cGMP-, especially for SNP-induced relaxation.
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