FUNCTIONAL-EFFECTS OF INTRACELLULAR PH ALTERATION IN THE HUMAN UTERUS- SIMULTANEOUS MEASUREMENTS OF PH AND FORCE

Changes in intracellular pH have differing effects on contraction in d ifferent types of muscle, and between species. Because of the large nu mber of women requiring a caesarean section due to failure to progress in labour, it is important to know how the human myometrium responds to the changes in intracellular pH that may occur during labour. The p H-sensitive dye, carboxy-SNARF, was used to measure intracellular pH i n small strips of human myometrium. Intracellular pH and tension were simultaneously recorded in pregnant and nonpregnant tissue. Intracellu lar pH was altered by the addition of weak acids and bases. Intracellu lar alkalinization caused an increase in the frequency and amplitude o f contractions. Intracellular acidification led to an initial increase in the frequency and/or the amplitude of the contractions, followed b y abolition of contractions. Alterations in intracellular pH had profo und effects on contraction in human uterine smooth muscle. Possible me chanisms are discussed whereby pH could influence force production, an d changes in contraction are related to the speed and extent of the ch ange in intracellular pH.