Abstract
It is known that alteration of the intracellular pH(pHi) significantly affects frequency and amplitude of spontaneous contraction in pregnant rat uterine smooth muscle. In this study we examined the effect of pHi change on (i) the spontaneous contraction and intracellular Ca2+ concentration ([Ca2+]i), (ii) the activity and kinetic property of the voltage‐dependent Ca2+ channel and the delayed rectifier K+ channel, and (iii) the activity of Ca2+‐activated K+ channel in pregnant rat myometrium. Intracellular acidosis (20mM Na+‐acetate) decreased in frequency and amplitude of spontaneous contractions. However, intracellular alkalosis (20mM NH4Cl) caused a tonic contraction or marked increase in frequency and amplitude of spontaneous contractions. The force was correlated with the [Ca2+]i transients. Intracellular acidosis decreased the magnitude of the voltage‐dependent Ca2+ current, but intracellular alkalosis increased it. Intracellular acidosis increased the delayed rectifier K+ current but intracellular alkalosis decreased it. Activity of Ca2+‐activated K+ channels (BKCa) was decreased by intracellular acidosis but increased by intracellular alkalosis. These results indicate that pH‐induced change of Ca2+ channels and K+ channels activity may be involved in the pH‐dependent modulation of spontaneous contraction in pregnant rat uterine smooth muscle.
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