EFFECT OF HYPOXIA ON FORCE, INTRACELLULAR PH AND CA2+ CONCENTRATION IN RAT CEREBRAL AND MESENTERIC SMALL ARTERIES

1. The effect of severe hypoxia on force, intracellular Ca2+ concentration ([Ca2+](i)) and pH, was studied in isolated small arteries from rat brain and rat mesenterium. The arteries were mounted for isometric force recording while [Ca2+](i) was measured with fura-2 or pH(i) was measured with bis-carboxyethylcarboxyfluorescein (BCECF). 2. Hypoxia reduced the force development in response Do arginine vasopressin (AVP) while [Ca2+](i) was unchanged or only slightly reduced. Inhibition of acid extrusion by omission of sodium caused no force development in mesenteric arteries, but the fall in pH(i) was enhanced during hypoxia. In cerebral arteries, hypoxia. reduced the force development associated with omission of sodium, and the fall in pH(i) was less than during normoxic conditions. When acid extrusion was intact, pH(i) was not affected by hypoxia and the changes in pH(i) during activation with AVP were similar during hypoxia and in the control situation. 3. Although a decrease in smooth muscle [Ca2+](i) may be partly responsible for the reduced force development during hypoxia, [Ca2+](i)-independent mechanism(s) may play an even more important role. Furthermore, although hypoxia and force development are associated with enhanced acid production, acid extrusion maintains pH(i) near the control level and it is unlikely that a decrease in smooth muscle pH(i) plays any role in the reduced force development during hypoxia.