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 variou s types of acidosis on vessel diameter, intracellular pH (pH(i)), and calcium concentration ([Ca2+](i)) in a cannulated preparation of the m esenteric arteriole of the rabbit. The effect of acidosis on vessel co ntraction was also studied in the wire-mounted preparation. In the can nulated preparation, pre-contracted by noradrenaline, hypercapnia caus ed vasoconstriction and increases in [Ca2+](i). In the wire-mounted pr eparation pre-contracted by either noradrenaline or high KCl, hypercap nia caused a transient vasoconstriction. In contrast, in the cannulate d preparation pre-contracted by high KCI hypercapnia caused a transien t vasorelaxation and decreases in [Ca2+](i). Intracellular acidosis, i nduced by a NH4Cl prepulse, caused vasoconstriction and increases in [ Ca2+](i) even in the cannulated preparation pre-contracted by high KCl . The decrease in pH(i) during hypercapnia was similar to that observe d after NH4Cl withdrawal. These data suggest that: (1) the effect of a cidosis 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 du ring acidosis. (C) 1996 Academic Press Limited