SIMULTANEOUS MEASUREMENTS OF ELECTRICAL-ACTIVITY, INTRACELLULAR [CA2-MUSCLE(] AND FORCE IN INTACT SMOOTH)

Although both electrical activity and changes in intracellular [Ca2+] are known to be important determinants of smooth muscle force, little is known about the relationship between the three in intact muscle. Th is is due to a lack of simultaneous measurements of these parameters, In this paper we describe how we have combined the sucrose gap techniq ue with microspectrophotometry and force recording in rat ureteric smo oth muscle. We have investigated the timecourses of the changes in the se parameters following physiological stimulation i.e. the action pote ntial. The results of this paper show that it is possible to simultane ously measure electrical activity, [Ca] and force in intact smooth mus cle and that (i) about a third of the change in Ca2+ occurs on the ups troke of the action potential and the remainder during the plateau. (i i) 50% of the decline in [Ca2+] occurs after the repolarization of the action potential and (iii) the kinetics of force development and rela xation are significantly slower than those of Ca2+, suggesting that [C a2+] is not rate-limiting. These are the first such simultaneous measu rements in any smooth muscle.