Endothelin-1 regulates cytosolic and nuclear Ca2+ in human endocardial endothelium

Endocardial endothelium is far less studied than its systemic and pulmonary counterparts and its role in cardiac function is not well known. In the st udy reported here, we succeeded in isolating and culturing endocardial endo thelial cells (EECs) from 21-week-old human fetal heart and verified whethe r endothelin-1 (ET-1) receptors are present on these cells and whether thei r activation regulates cytosolic ([Ca](c)) and nuclear calcium ([Ca](n)). U sing fluo-3 Ca2+ measurement and three-dimension confocal microscopy techni ques, superfusion of fetal human EECs from right and left ventricles with i ncreasing concentrations of ET-1 induced a dose-dependent sustained increas e of free cytosolic and nuclear Ca2+ levels with an EC50 near 10(-10) M and 10(-11) M. respectively. The sustained increase of cytosolic and nuclear C a2+ by ET-1 in both EEC preparations was completely blocked by the calcium chelator ethylene glycol-his (beta -aminoethylether)-N,N,N',N'-tetra-acetic acid (EGTA) but was insensitive to the L-type Ca2+ channel blocker, nifedi pine. The effect of ET-1 was prevented by the ETA-receptor antagonist BQ 12 3. However the ETB-receptor antagonist BQ 788 had no effect. Our results su ggest that ET-1 receptors are present in human EECs and that their stimulat ion induces sustained Ca2+ influx through ETA-receptor stimulation of a nif edipine-insensitive Ca2+ channel, probably the R-type Ca2+ channel. The pre sence of Ca2+-dependent responses to ET-1 supports a possible modulatory ro le of the endocardial endothelium in myocardial functions.