Effects of Phenylephrine on the Contractile Tension and Cytosolic Ca2+ Level in Rat Anococcygeus Muscle.

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A contractile propertiy of phenylephrine (PE), α1 agonist, on rat anococcygeus muscle was compared with that on rat aorta by simultaneously measuring changes in intracellular Ca2+ ([Ca2+] 1) level and muscle tension.(1) PE (0.1-30, μ M) and high K+induced a sus tained increases in [Ca2+] 1 level and muscle tension of both the muscles.(2) An application of verapamil (10μM) and EGTA (4mM) decreased the PE or high K+-increased tension and [Ca2+] 1 level in both the muscle, respectively.(3) A cumulative application of PE or high K+to anococcygeus muscle and aorta exhibited a positive relationship between [Ca2+] 1 and developed tension. The developed tension by PE was greater than that by high K+at the same level of [Ca2+] 1 only in the aorta. A difference of regression slopes in the relationship between [Ca2+] 1 level and muscle tension under PE and high K+-treatments in aorta was significant, but that in anococcygeus muscle was not.(4) An application of PE to anococ cygeus muscle in Ca2+free medium elicited a small transient contractile tension and increase in [Ca2+] 1 level, but that to aorta showed a large and transient increase in both the parameters.(5) Phorbol ester, DPB (1μM), did not affect muscle tension or [Ca2+] 1 level in anococcygeus muscle, but DPB induced greater increases in aorta.(6) An application of PE (10μM) with GTP produced a left shift in the pCa-tension curve in the β-escin-permeabilized fiber of the anococcygeus muscle. In summary, it is suggested that the sustained contraction induced by PE in anococ cygeus muscle is involved with the increases in [Ca2+] 1 which is due to Ca2+influx mediated by a, receptor, but scarecely to Ca2+release from the intracellular storage, and that an increase in Ca2+sensitivity to PE is found only in the permeabilized anococcygeus muscle. The Ca2+-independent contractile mechanism in PE response as seen in aorta is probably to be absent in anococcygeus muscle. Moreover, it seems that the effect of the drug acting protein kinase C on anococcygeus muscle is extremely lesser than that on aorta.
日本平滑筋学会の論文

Effects of Phenylephrine on the Contractile Tension and Cytosolic Ca2+ Level in Rat Anococcygeus Muscle.

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