Effect of acidosis on contraction, intracellular pH and calcium in the rabbit mesenteric small artery.

The purpose of the present study was to determine the effect of various types of acidosis on vessel diameter, intracellular pH (pHi), and calcium concentration ([Ca2+]i) in a cannulated preparation of the mesenteric arteriole of the rabbit. The effect of acidosis on vessel contraction was also studied in the wire-mounted preparation. In the cannulated preparation, pre-contracted by noradrenaline, hypercapnia caused vasoconstriction and increases in [Ca2+]i. In the wire-mounted preparation pre-contracted by either noradrenaline or high KCl, hypercapnia caused a transient vasoconstriction. In contrast, in the cannulated preparation pre-contracted by high KCl, hypercapnia caused a transient vasorelaxation and decreases in [Ca2+]i. Intracellular acidosis, induced by a NH4Cl prepulse, caused vasoconstriction and increases in [Ca2+]i even in the cannulated preparation pre-contracted by high KCl. The decrease in pHi during hypercapnia was similar to that observed after NH4Cl withdrawal. These data suggest that: (1) the effect of acidosis on vascular tone and [Ca2+]i is different depending upon the type of preparation and the mode of pre-activation, and (2) [Ca2+]i may, at least partly, regulate vascular contraction and relaxation during acidosis.