SPATIAL-DISTRIBUTION OF RECEPTORS TO VARIOUS VASOACTIVE SUBSTANCES ININTACT GUINEA-PIG ENDOCARDIAL ENDOTHELIUM

The responses of guinea-pig endocardial endothelial (EE) cells to vari ous vasoactive substances were investigated in a small tissue preparat ion by recording the membrane potential using the nystatin-perforated patch clamp technique. The resting potential of the EE cells was -44.4 +/- 0.8 mV (n = 118) when the patch electrode was applied to the EE c ells at the endocardial surface of the small tissue preparation. The a pplication of ATP 10 mu M, ADP 10 mu M, AMP 10 mu M, adenosine 10 mu M , histamine 10 mu M, and substance P 1 mu M induced transient hyperpol arizations. The rate of observing responses varied among the agonists. Most preparations responded to ATP, ADP, and histamine while response s to AMP or adenosine appeared only in 20%-30% of the preparations. In contrast to vascular endothelial cells, the membrane potential of EE cells failed to respond to acetylcholine, bradykinin, and thrombin. At rial natriuretic peptide, vasopressin, and serotonin also failed to ev oke any changes in the membrane potential. These findings may suggest that EE cells have a different set of receptors from that of vascular endothelial cells.