Electro- and Pharmacomechanical Coupling in the Smooth Muscle Cells of the Rabbit Ear Artery

A ~ S T R A C T A contraction of the rabbit ear ar tery can be induced by depola r iz ing the cells with a K-rich solution if Ca is present . 10 -9-10 -8 M no rad rena l ine and 10 -s10 -7 M his tamine cause a contraction of this tissue without modify ing the m e m brane potent ial . If the his tamine concent ra t ion exceeds 10 -~ M some depolar iza t ion of the membrane also occurs. Both norad rena l ine and h is tamine also induce a contraction in Ca-f ree m e d i u m , even if La is present . N o n e of these stimuli produces act ion potent ia ls o r fluctuations of the m e m b r a n e potent ia l . Besides these tonic contractions, the ear ar tery can also p roduce phasic contract ions when 10 mM T E A is added to the medium. Such contractions are caused by the appear ance o f action potentials which are Ca d e p e n d e n t and which are similar to those a p p e a r i n g in visceral smooth muscle. A study of 4SCa fluxes has revea led that K depolar iza t ion and no rad rena l i ne cause only a small increase in 4SCa uptake by the cells, while no rad rena l ine also releases cel lular Ca, even in Caf ree m e d i u m . A compar i son of tension d e v e l o p m e n t and 45Ca release induced by no rad rena l i ne in Ca-f ree m e d i u m suggests that Ca ex t rus ion could be very eff icient in the rabbit ear ar tery and that it could play a direct role in its re laxat ion.