OCCURRENCE OF INTRACELLULAR PH TRANSIENTS DURING SPONTANEOUS CONTRACTIONS IN RAT UTERINE SMOOTH-MUSCLE

1. Intracellular pH (pH(i)) and contraction have been measured simulta neously in isolated longitudinal rat myometrium. Tissue was loaded wit h the pH-sensitive fluorophore carboxy-SNARF and superfused with oxyge nated, buffered salt solution at 37-degrees-C and pH 7.4. 2. Small (0. 04 pH unit) transient intracellular acidifications followed each spont aneous uterine contraction. The pH(i) transients lagged contraction by 15 s. Removal of external Ca2+ abolished both spontaneous contraction s and the pH(i) changes. 3. Increasing uterine contraction by depolari zation (40 mm K+) or agonist (50 mum carbachol) produced a larger acid ification (0.18 pH unit). 4. The acidification with contraction does n ot appear to be due to increased glycolysis as no increase in lactate efflux occurred with high-K+ stimulation. 5. Uterine contraction is kn own to be sensitive to changes in pH(i). Comparable pH(i) changes to t he pH(i) transients seen during spontaneous contraction were induced b y application and withdrawal of weak acids and bases. The resulting pH (i) changes (0.02-0.08 pH unit) produced effects on contraction freque ncy and amplitude, alkalinization augmenting and acidification depress ing contractile activity, suggesting that the pH(i) transients with co ntraction are functionally important.