Intracellular pH (pHi) is a critical factor influencing many important cellular functions.
Acid extrusion carriers such as an Na⁺/H⁺ exchanger (NHE) Na⁺/HCO₃⁻ cotransporter (NBC) and monocarboxylate transporters (MCT) can be activated when cells are in an acidic condition (pHi < 7.1). Human radial artery smooth muscle cells (HRASMC) is an important conduit in
coronary artery bypass graft surgery. However, such far, the pHi regulators have not been characterized in HRASMCs. We therefore investigated the mechanism of pHi recovery from intracellular
acidosis and
alkalosis, induced by NH₄Cl-prepulse and Na-
acetate-prepulse, respectively, using intracellular 2',7'-bis(2-carboxethyl)-5(6)- carboxy-
fluorescein (
BCECF)-fluorescence in HRASMCs. Cultured HRASMCs were derived from the segments of human radial artery that were obtained from patients undergoing bypass grafting. The resting pHi is 7.22 ± 0.03 and 7.17 ± 0.02 for
HEPES- (nominally HCO₃⁻-free) and CO₂/HCO₃⁻- buffered
solution, respectively. In
HEPES-buffered
solution, a pHi recovery from induced intracellular
acidosis could be blocked completely by 30 μM
HOE 694 (3-methylsulfonyl-4-piperidinobenzoyl, guanidine hydrochloride) a specific NHE inhibitor, or by removing [Na⁺]₀. In 3% CO₂/HCO₃⁻-buffered
solution,
HOE 694 slowed the pHi recovery from the induced intracellular
acidosis only, while adding together with
DIDS (a specific NBC inhibitor) or removal of [Na⁺]₀ entirely inhibited the
acid extrusion. Moreover, α-cyano-4-hydroxycinnamate (CHC; a specific blocker of MCT) blocked the
lactate-induced pHi changes. In conclusion, we demonstrate, for the first time, that 3 different pHi regulators responsible for
acid extruding, i.e. NHE and NBC, and MCT, are functionally co-existed in cultured HRASMCs.