17-BETA-ESTRADIOL INHIBITS THE VOLTAGE-DEPENDENT L-TYPE CA2-MUSCLE CELLS( CURRENTS IN AORTIC SMOOTH)

To elucidate the mechanisms of estrogens-induced relaxation effects on vascular smooth muscle cells, the effects of estrogens and the relate d hormones were examined in cultured rat thoracic aortic smooth muscle cell lines (A7r5), using the whole-cell voltage clamp technique. The patch pipette was filled with 140 mM CsCl- or KCl-containing internal solution. With CsCl-internal solution, 17 beta-estradiol and synthetic estrogens, ethynylestradiol and diethylstilbestrol (0.1-30 mu M) inhi bited the Ba2+ inward current (I-Ba) through the voltage-dependent L-t ype Ca2+ channel in a concentration-dependent and reversible manner. T he potency of the inhibitory effects on I-Ba was 17 beta-estradiol < e thynylestradiol < diethylstilbestrol. 17 beta-Estradiol (10 mu M) appe ared to reduce the maximal conductance of I-Ba with only a slight shif t of voltage-dependency of inactivation and to affect I-Ba in a use-in dependent fashion. On the other hand, testosterone and progesterone (3 0 mu M) failed to affect I-Ba. At a holding potential of -40 mV, both vasopressin and endothelin-1 (100 nM) activated a long-lasting inward current. After endothelin-l (100 nM) activated the current, the additi onal application of vasopressin (100 nM) could not induce it furthermo re, suggesting that each agonist activates the same population of the channels. The reversal potential of the current was about 0 mV and was not significantly altered by replacement of [Cl-], or [Cl-], and the inward current was also observed even when extracellular cations are C a2+, proposing that it was a Ca2+-permeable non-selective cation chann el (I-N.S.). La3+ or Cd2+ (1 mM) completely abolished I-N.S., however, nifedipine (10 mu M) failed to inhibit it at all. Diethylstilbestrol (1-30 mu M) suppressed the I-N.S. evoked by both endothelin-l and vaso pressin in a concentration-dependent manner, while 17 beta-estradiol, ethynylestradiol, progesterone and testosterone (30 mu M) failed to in hibit it significantly. In addition, at a holding potential of +0 mV, 17 beta-estradiol by itself did not affect the holding currents, and d id not inhibit K+ currents evoked by endothelin-l or vasopressin, poss ibly due to the Ca2+ release from the storage sites. These results sug gest that 17 beta-estradiol may play a role in regulating vascular ton e, selectively by inhibiting the voltage-dependent L-type Ca2+ current in vascular smooth muscle cells.