PHARMACOLOGICAL CHARACTERIZATION OF IONOPHORE X537A-INDUCED CONTRACTILE RESPONSES IN ISOLATED RABBIT TAENIA COLI AND AORTA

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Pharmacological action of ionophore X537A was studied in taenia coli and aortic strips isolated from rabbit. These isolated smooth muscle preparations contracted by X537A (10^<-5>-10^<-4> M). A removal of Ca ions from the buffer solution considerably reduced the contraction of taenia coli but not that of aorta. D 600 (methoxyverapamil, 10^<-6> M) was without any effect in the contraction of both tissues by X537A (10^<-4> M). However, papaverine (10^<-4> M) and Aspaminol (1,1-diphenyl-3-piperidinobutanol hydrochloride, 10^<-4> M) inhibited X537A (10^<-4> M)-induced contraction markedly in taenia coli but slightly in aorta. Inhibitory effects of these drugs were reversed in taenia coli by increasing Ca ion concentration in buffer solution but not in aorta. X537A (10^<-4> M)-induced contraction of aorta was not affected by a pretreatment of rabbit with reserpine and preincubation of the isolated preparations with guanethidine (10^<-6> M) or prazosin (10^<-7> M). These results suggest that ionophore X537A might produce the contraction through an increase of Ca influx in isolated rabbit taenia coli which are little or not affected by D 600,whereas the contraction of rabbit aorta induced by X537A is mainly due to facilitation of release of Ca sequestered intracellularly.
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