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Am J Physiol Heart Circ Physiol 275: H1351-H1359, 1998;
0363-6135/98 $5.00
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Vol. 275, Issue 4, H1351-H1359, October 1998

Intracellular acidosis differentially regulates KV channels in coronary and pulmonary vascular muscle

Marcie G. Berger1, Christophe Vandier2, Pierre Bonnet2, William F. Jackson3, and Nancy J. Rusch1

1 Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226; 2 Laboratoire de Physiologie des Cellules Cardiaques et Vasculaires, Centre National de la Recherche Scientifique Université Francois-Rabelais 6542, Tours, France; and 3 Department of Biological Sciences, Western Michigan University, Kalamazoo, Michigan 49008

Decreases in intracellular pH (pHi) potently dilate coronary resistance arteries but constrict small pulmonary arteries. To define the ionic mechanisms of these responses, this study investigated whether acute decreases in pHi differentially regulate K+ currents in single vascular smooth muscle (VSM) cells isolated from rat coronary and pulmonary resistance arteries. In patch-clamp studies, whole cell K+ currents were elicited by 10-mV depolarizing steps between -60 and 0 mV in VSM cells obtained from 50- to 150-µm-OD arterial branches, and pHi was lowered by altering the NH4Cl gradient across the cell membrane. Progressively lowering pHi from calculated values of 7.0 to 6.7 and 6.4 increased the peak amplitude of K+ current in coronary VSM cells by 15 ± 5 and 23 ± 3% but reduced K+ current in pulmonary VSM cells by 18 ± 3 and 21 ± 3%, respectively. These changes were reversed by returning cells to the control pHi of 7.0 and were eliminated by dialyzing cells with pipette solution containing 50 mmol/l HEPES to buffer NH4Cl-induced changes in pHi. Pharmacological block of ATP-sensitive K+ channels and Ca2+-activated K+ channels by 1 µmol/l glibenclamide and 100 nmol/l iberiotoxin, respectively, did not prevent changes in K+ current levels induced by acidotic pHi. However, block of voltage-gated K+ channels by 3 mmol/l 4-aminopyridine abolished acidosis-induced changes in K+ current amplitudes in both VSM cell types. Interestingly, alpha -dendrotoxin (100 nmol/l), which blocks only select subtypes of voltage-gated K+ channels, abolished the acidosis-induced decrease in K+ current in pulmonary VSM cells but did not affect the acidosis-induced increase in K+ current observed in coronary VSM cells. These findings suggest that opposing, tissue-specific effects of pHi on distinct subtypes of voltage-gated K+ channels in coronary and pulmonary VSM membranes may differentially regulate vascular reactivity in these two circulations under conditions of acidotic stress.

coronary arteries; pulmonary arteries; potassium channels; pH; ammonium chloride; vascular smooth muscle


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