Classification of ion channels in the luminal and abluminal membranes of guinea-pig endocardial endothelial cells.

1. The ion channels on both the luminal and abluminal membranes of endocardial endothelial (EE) cells were separately recorded using the patch clamp technique in the guinea-pig heart. 2. The major population consisted of two types of non-selective cation channels, which showed open probabilities of 0.21 and 0.33 at the resting potential, and conductances of 36 and 11 pS, respectively. 3. The next major class was Cl- channels with an ohmic conductance of 409 pS. The channel was quiescent in the cell-attached mode but was activated by strong depolarization after excising the patch membrane. 4. The channels activated by intracellular Ca2+ were mainly K+ channels showing a 34 pS slope conductance and, less frequently, Ca(2+)-dependent K+ channels having a large conductance (210 pS). The inward rectifier K+ channel (32 pS) was also observed. 5. The non-selective cation channels were recorded on the luminal membrane, but scarcely on the abluminal membrane, suggesting an active transport of K+ and Na+ across the endocardium. 6. The resting membrane conductance of the EE cells may be provided mostly by non-selective cation channels and 34 pS Ca(2+)-dependent K+ channels.