MECHANISMS OF PH(I) CONTROL AND RELATIONSHIPS BETWEEN TENSION AND PH(I) IN HUMAN SUBCUTANEOUS SMALL ARTERIES

Intracellular pH (pH(i)) control and relationships between pH(i) and tension have been investigated in human subcutaneous small arteries. Isometric tension and pH(i) (using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein) were estimated simultaneously. pH(i) recovery from an acute acid load was dependent on external Na+ and partially inhibited by the absence of HCO3- [N-2-hydroxyethylpiperazine-N'-2-ethane-sulfonic acid (HEPES)-buffered solution] or by the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIES). In an HCO3--buffered physiological salt solution (PSS), pH(i) recovery was partially blocked by hexamethylene amiloride (HMA), an inhibitor of Na+/H+ exchange, and completely blocked by DIDS and HMA together. Intracellular Cl- depletion of arteries did not affect the rate of pH(i) recovery in PSS from an acid load. pH(i) recovery from acute alkalosis was unaffected by external Na+ removal, reduced in HEPES buffer, and abolished by removal of external Cl-. These data suggest that human small arteries maintain pH(i) by Na+/H+ exchange and Na+-dependent HCO3- exchange in response to an acid load, and Nat-independent Cl-/HCO3- exchange to counteract intracellular alkalosis. Norepinephrine (NE)-, endothelin-l (ET-1)-, arginine vasopressin (AVP)-, and K+-induced tension did not alter pH(i) in PSS, but there was a small fall with angiotensin II (ANG II). In HEPES, stimulation with K+, NE, ANG II, or AVP led to a fall in pH(i), but this did not occur with ET-1. It is therefore unlikely in vivo that an increase in pH(i) in these arteries would be involved in either tension development or growth induced by these agonists.