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

Abstract

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, α-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.

Changes in pH Increase Perfusion Pressure of Coronary Arteries in the Rat

“…Changing the pH of the perfusate from 7.4 to alkaline pH resulted in an increase of coronary perfusion pressure in both WKY and SHR, confirming previous reports (5,19). However, effects of acidic pH on coronary arteries in normotensive rats have been controversial (8,18). Moreover, previous reports paid no attention to the blood pressure in rats.…”

“…Vasoactive responses to acidification in vascular smooth muscles are often opposite, i.e., relaxation and contraction. Opposite responses are likely to be due to differences in vascular bed and species (3,7,8). However, effects of pH i on vascular smooth muscles have been unclear.…”

“…However, previous reports were controversial. While, it was reported that acidosis caused vasodilation in coronary arteries of the Sprague-Dawley rat (8), pig (15,16), and dog (17), Wilson and Woodward (18) reported that acidosis induced coronary constriction in the rat heart. The animals used in these reports were all normotensive, and the effect of acidosis on coronary arteries in hypertensive animals was not investigated.…”

Dichloroacetate, a Metabolic Modulator, Prevents and Reverses Chronic Hypoxic Pulmonary Hypertension in Rats

“…The current-density data and the voltage dependence of the I K in PASMCs in this report are within the range published in the literature. [25][26][27][28] Variability in these values can be explained in part by differences in the enzymatic dispersion techniques and the specific vascular sections used, because there is regional diversity in the expression of K ϩ channels within the pulmonary circulation. 28 In addition to the long-term effects of DCA, we show that this drug can increase I K in the short term much more rapidly and at much lower doses than previously described (mol/L versus mmol/L), indicating novel and previously unrecognized properties of DCA.…”

P-Glycoprotein-Mediated Efflux and Drug Sequestration in Lysosomes Confer Advantages of K562 Multidrug Resistance Sublines to Survive Prolonged Exposure to Cytotoxic Agents

“…Nevertheless, the intracellular free H + could vary in response to different stimuli. Evidences indicated that intracellular protons could serve as a second messenger in regulating multiple cellular functions [22,23] .…”