Ion channels in the luminal membrane of endothelial cells of the bull-frog heart.

Abstract

Ion channels in the luminal membrane of intact endothelial cells of the bull-frog atrium were examined with single channel recordings. A class of outwardly rectifying channels and at least two types of ohmic channels were recorded without any stimulation by vasoactive substances. The slope conductances of the outwardly rectifying channel measured at potentials positive to and negative to the reversal potential were 36.4 +/- 8.8 and 7.5 +/- 2.2 pS, respectively (n = 35). This channel was a cation channel with poor selectivity between K+ and Na+ (PNa/PK = 1.04 +/- 0.08, n = 3). The open probability and mean open time increased as the membrane was depolarized. The two ohmic channels had single channel conductances of 175.3 +/- 17.7 (n = 21) and 9.5 +/- 1.8 pS (n = 11), respectively. The 175pS channel also failed to discriminate between K+ and Na+. Its open probability was voltage-independent. Internal Ca2+ affected none of the channels examined. The luminal membrane may have a population of ion channels different from the abluminal membrane. These characteristics were different from those so far described in the cultured endothelial cells from mammalian blood vessels.