NONSELECTIVE CATION CURRENT OF GUINEA-PIG ENDOCARDIAL ENDOTHELIAL-CELLS

1. Endocardial endothelial (EE) cells, isolated by the enzymatic treat ment of guinea-pig heart, mere used for whole-cell voltage clamp exper iments. 2. The inward rectifier K+ current was observed in about half of the experiments. The contribution of Ca2+-dependent K+ current to t he resting membrane conductance was also suggested. 3. After the K+ co nductances were suppressed, removal of external Na+ revealed an inward cation current (1.2 pA pF(-1), at -45 mV), whose slope conductance wa s a saturable function of external Na+ concentration. When Na+ was tot ally replaced by various monovalent cations, the order of the membrane conductances was K+ > Rb+ > Cs+ > Na+ > Li+. 4. This basal non-select ive cation current was blocked by either Gd3+ or La3+, and showed slig ht out ward rectification. 5. Addition of 20 mM Ca2+ or Ba2+, but not Mg2+ or Mn2+, to the Na+-free solution, induced an inward current, ind icating that this current possesses a significant Ca2+ permeability. 6 . In similar to 15% of the experiments, ATP and histamine induced anot her type of non-selective cation current, which showed different ion s electivity (Na+ > K+, Cs+) and rectification (inward). 7. The basal no n-selective cation current is responsible for both the low resting pot ential and the leak Ca2+ influx of EE cells.