- Japan Society of Smooth Muscle Research
- 日本平滑筋学会雑誌 (ISSN:03743527)
- vol.21, no.1, pp.57-69, 1985
Aschoori, F., Hidaka, H., Takai, A. & Tomita, T. <I>Contraction of smooth muscle in Ca-free solution</I>. Japanese Journal of Smooth Muscle Research, 1985, 21 (1), 57-69.-The tonic contractions which are extremely resistant to removal of the external Ca were investigated in the rat was deferens and myometrium. Both the noradrenaline response in the was deferens and the oxytocin response in the myometrium could be repeatedly produced without appreciable diminution in Ca-free solution for more than 24hrs. On the other hand, the tissue Ca content decreased exponentially after Ca-removal with a half time of 130-180min. When Ca was readmitted, no indication of the early transient contraction was observed in the subsequent response in Ca-free solution, but the response was reduced compared with the response before Ca readmission. Verapamil suppressed the response in the presence of Ca, while it had very weak inhibitory effect even at 10μM. Calmodulin antagonists of phenothi-azine derivatives had a strong inhibitory effect on Ca-induced contractions, whereas they had very weak effects on the receptor-mediated contraction in Ca-free solution. Another calmodulin antagonist, W-7 suppressed both Ca-induced contraction and the contractions independent of external Ca. HA-1004, a vasodilator which has a struc-ture similar to W-7, reduced the receptor-mediated contraction in Ca-free solution without much effect on Ca-induced contractions. These results may suggest that the receptor-mediated contractions resistant to Ca-removal are caused by some process without a contribution of the Ca-calmodulin system.