PH effects on high conductance Ca 2+-activated K + channels (BK Ca) in human internal mammary artery smooth muscle cells

Abstract

Introduction In vascular smooth muscle cells, different types of K + channels participate in the regulation of membrane potential and consequently in the contractile behavior of the vessel. There is little information about the properties and role of K + channels in human internal mammary artery (HIMA), the vessel of choice for coronary revascularization. Methods Patch-clamp technique on isolated HIMA smooth muscle cells was used. Results This work presents for the first time single-channel properties of the high conductance Ca 2+-activated K + channel (BK Ca) of HIMA. It presents a single-channel conductance of 228 ± 4 pS ( n = 44, 8 cells), is sensitive to 100 nM iberiotoxin, and its open probability is Ca 2+- and voltage-dependent. Inside-out results show that BK Ca channels in HIMA are directly activated by increasing the pH of intracellular media ( NPo = 0.096 ± 0.032 at pH 7.4 and NPo = 0.459 ± 0.111 at pH 7.6, n = 12 cells, p < 0.05) and inhibited by lowering this pH ( NPo = 0.175 ± 0.067 at pH 7.4 and NPo = 0.051 ± 0.019 at pH 6.8, n = 13 cells, p < 0.05). Conclusions The evidences presented about single-channel properties and intracellular pH sensitivity of BK Ca from HIMA smooth muscle cells provide useful information to elucidate physiological or pathological mechanisms in this vessel, as well as for future studies where drugs could have BK Ca channels as targets for pharmacological therapies.