The Effect and Underlying Mechanism of Ethanol on Intracellular H + ‐Equivalent Membrane Transporters in Human Aorta Smooth Muscle Cells

Background The presence of intracellular pH (pH i ) regulators, including Na + –H + exchanger ( NHE ), Na + – HCO 3 − co‐transporter ( NBC ), Cl − / OH − exchanger ( CHE ), and Cl − / HCO 3 − exchanger ( AE ), have been confirmed in many mammalian cells. Alcohol consumption is associated with increased risk of cardiovascular disorder. The aims of the study were to identify the possible transmembrane pH i regulators and to explore the effects of ethanol (EtOH) (10 to 300 mM) on the resting pH i and pH i regulators in human aorta smooth muscle cells (HASMCs). Methods HASMCs were obtained from patients undergoing heart transplant. The pH i was measured by microspectrofluorimetry with the pH ‐sensitive dye, BCECF ‐AM. Results The following results are obtained. (i) In cultured HASMC s, the resting pH i was 7.19 ± 0.04 and 7.13 ± 0.02 for HEPES ‐ and CO 2 / HCO 3 − ‐buffered solution, respectively. (ii) Two different Na + ‐dependent acid‐equivalent extruders, including NHE and Na + ‐coupled HCO 3 − transporter, functionally coexisted. (iii) Two different Cl − ‐dependent acid loaders ( CHE and AE ) were functionally identified. (iv) EtOH induced a biphasic, concentration‐dependent change in resting pH i (+0.25  pH unit at 100 mM but only +0.05 pH unit at 300 mM) in bicarbonate‐buffered solution, while caused a concentration‐dependent decrease in resting pH i (−0.06 pH unit at 300 mM) in HEPES ‐buffered solution. (v) The effect of EtOH on NHE activity was also biphasic: increase of 40% at lower concentration of 10 mM, followed by decrease of 30% at higher concentration of 300 mM. (vi) The increase in Na + ‐coupled HCO 3 − transporter activity by EtOH was concentration dependent. (vii) The effect of EtOH on CHE and AE activities was both biphasic: increase of ~25% at 30 mM, followed by decrease of 10 to 25% at 100 mM, and finally increase of 15 to 20% at 300 mM. Conclusions This study demonstrated that 2 acid extruders and 2 acid loaders coexisted functionally in HASMC s and that EtOH induced a biphasic, concentration‐dependent change in resting pH i by altering the activity of the 2 acid extruders, NHE and Na + ‐coupled HCO 3 − transporter, and the 2 acid loaders, CHE and AE .