SIMULTANEOUS MEASUREMENT OF INTRACELLULAR PH AND CONTRACTION IN UTERINE SMOOTH-MUSCLE

Changes in intracellular pH (pH(i)) are thought to produce large chang es in force production in the uterus. There have however, been no simu ltaneous measurements of pH(i) and force in the uterus and therefore n o direct information is available about the relation between the two. We have used carboxy-SNARF (a pH-sensitive fluorophore) in small strip s of longitudinal myometrium and obtained simultaneous measurements of pH(i) and force. SNARF did not alter contractile function, and contin uous measurements of pH(i) could be made for 2 hours. The mean resting pH(i) (7.16) was similar to that reported previously. Application of weak bases rapidly raised pH(i), in a concentration-dependent manner, followed by a gradual restoration of pH(i) to resting levels. Alkalini zation greatly increased the frequency of contractions, often accompan ied by a small increase in their amplitude. Removal of base produced a rebound acidification which transiently abolished contractions. Direc t acidification of the cytoplasm, by application of weak acid, also ab olished contractions. However the alkalinization which accompanied rem oval of acid, produced variable effects on force.