Presence of functional endothelin-1 receptors in nuclear membranes of human aortic vascular smooth muscle cells

Our previous work showed that the nucleus plays a role in excitation-contraction coupling and that the channels and receptors could be present at the nuclear membrane. In the study reported here, the objective was to test the hypothesis that endothelin-1 (ET-1) receptors are functional at the level of the nuclear membranes and that their stimulation importantly regulates free nucleoplasmic Ca2+ level. Using a Flue-3 Ca2+ measurement technique in human vascular smooth muscle cells (HVSMC), superfusion with increasing concentrations of extracellular ET-1 induced a dose-dependent sustained increase of free cytosolic ([Ca](c)), nuclear ([Ca](n)) Ca2+ and contraction with an EC50 near 3 x 10(-10) hi. Like the extracellular ET-1, the cytosolic application of ET-1 using the perforated sarcolemma membrane technique, induced a dose-dependent increase of nuclear free calcium of HVSMC with an EC50 of 2 x 10(-11) M. These results strongly suggest that ET-1 receptors are functional at the level of the nuclear membranes. Furthermore, the sensitivity of ET-1 receptors at the nuclear membrane level seems to be higher than that of the receptors at the sarcolemma membrane. Finally, our results suggest that cytosolic ET-1 may play a role in preventing HVSMC nuclear calcium overload, thus protecting the cells from apoptosis.