In smooth muscle, the cytosolic Ca2+ concentration ([Ca2+]i) is the primary determinant of contraction, and the intracellular pH (pHi) modulates contractility. Using fura-2 and 2′,7′-biscarboxyethyl-5(6) carboxyfluorescein (BCECF) fluorometry and rat aortic smooth muscle cells in primary culture, we investigated the effect of the increase in pHi on [Ca2+]i. The application of the NH4Cl induced concentration-dependent increases in both pHi and [Ca2+]i. The extent of [Ca2+]i elevation induced by 20 mM NH4Cl was approximately 50% of that obtained with 100 mM K+-depolarization. The NH4Cl-induced elevation of [Ca2+]i was completely abolished by the removal of extracellular Ca2+ or the addition of extracellular Ni2+. The 100 mM K+-induced [Ca2+]i elevation was markedly inhibited by a voltage-operated Ca2+ channel blocker, diltiazem, and partly inhibited by a non-voltage-operated Ca2+ channel blocker, SKF96365. On the other hand, the NH4Cl-induced [Ca2+]i elevation was resistant to diltiazem, but was markedly inhibited by SKF96365. It is thus concluded that intracellular alkalinization activates the Ca2+ influx via non-voltage-operated Ca2+ channels and thereby increases [Ca2+]i in the vascular smooth muscle cells. The alkalinization-induced Ca2+ influx may therefore contribute to the enhancement of contraction.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology