POTASSIUM CURRENTS IN CULTURED HUMAN PULMONARY ARTERIAL SMOOTH-MUSCLECELLS

In this study, using whole cell and single-channel configurations of t he patch-clamp technique, we characterized K+ currents (I-K) in cultur ed human pulmonary arterial smooth muscle cells. The net whole cell ou tward membrane current (I-Ko) was activated at potentials positive to -60 mV. One component of I-Ko, I-K(dr), was inhibited by 4-aminopyridi ne (4-AP) and high concentrations of tetraethylammonium (TEA) but was Ca2+ and charybdotoxin (CTX) insensitive. The other component of I-Ko, I-K(Ca), was voltage and Ca2+ dependent and was inhibited by CTX and low concentrations of TEA. Activation of I-Ko in single-channel record ings was voltage dependent and demonstrated a high-conductance channel (245 +/- 2 pS) that was Ca2+ and CTX sensitive [I-K(Ca)] and a low-co nductance channel (109 +/- 2 pS) that was inhibited by 4-AP [I-K(dr)] but was insensitive to low concentrations of TEA or to an increase in intracellular [Ca2+]. In isolated pulmonary arterial rings, TEA and 4- AP caused an additive increase in arterial tension. To our knowledge t hese data provide the first characterization of the I-K in human pulmo nary arterial smooth muscle cells and indicate that I-K(Ca), and I-K(d r) play an important role in maintaining pulmonary vascular tone. The data confirm previous observations in pulmonary smooth muscle cells of animal models.