Simultaneous measurement of intracellular pH, calcium, and tension in rat mesenteric vessels: Effects of extracellular pH

In rat mesenteric vessels changes in external pH (pH(o)) alter tension. Changes in intracellular pH (pH(i)) and calcium ([Ca2+](i)) have both been suggested to underlie the tension changes. As no simultaneous measurements of pH(i) and [Ca2+](i) had been made, however, the relative importance and temporal relationship between pH(i) [Ca2+](i) and tension were unknown. In order therefore to gain a clearer understanding of the mechanisms involved, we have made simultaneous measurements of these parameters using carboxy-SNARF and INDO-1. Raising pH(o) caused rises in pH(i), Ca2+ and tension. The increases in pH(i) preceded increases in [Ca2+](i), which preceded the increases in tension. Similar but opposite effects were observed when pH(o) was decreased. We conclude that the change in [Ca2+](i) upon alteration of pH(o) is subsequent to that of pH(i). (C) 1996 Academic Press, Inc.