Inwardly rectifying K+ channels in esophageal smooth muscle

Abstract

The whole cell patch-clamp technique was used to investigate whether there were inwardly rectifying K+(Kir) channels in the longitudinal muscle of cat esophagus. Inward currents were observable on membrane hyperpolarization negative to the K+ equilibrium potential ( E k) in freshly isolated esophageal longitudinal muscle cells. The current-voltage relationship exhibited strong inward rectification with a reversal potential ( E rev) of −76.5 mV. Elevation of external K+ increased the inward current amplitude and positively shifted its E rev after the E k, suggesting that potassium ions carry this current. External Ba2+ and Cs+ inhibited this inward current, with hyperpolarization remarkably increasing the inhibition. The IC50 for Ba2+ and Cs+ at −60 mV was 2.9 and 1.6 mM, respectively. Furthermore, external Ba2+ of 10 μM moderately depolarized the resting membrane potential of the longitudinal muscle cells by 6.3 mV while inhibiting the inward rectification. We conclude that Kir channels are present in the longitudinal muscle of cat esophagus, where they contribute to its resting membrane potential.