RAPID MODULATION OF L-TYPE CALCIUM CURRENT BY ACUTELY APPLIED ESTROGENS IN ISOLATED CARDIAC MYOCYTES FROM HUMAN, GUINEA-PIG AND RAT

Gender-based differences in cardiovascular mortality may be due to a c ardio-protective effect of oestrogens on the myocardium. However, mRNA expression of oestrogen receptors in myocardial tissue of the adult h eart has yet to be demonstrated. Furthermore, a calcium antagonistic a ction of 17 beta-oestradiol on myocardial tissue has been discussed. T herefore, two subjects were investigated in atrial myocytes of the hum an, and ventricular myocytes of guinea-pig and rat in this study. (1) Are oestrogen receptors expressed in adult myocardial cells? (2) Is th ere an influence of oestrogens on the L-type calcium current of cardia c myocytes? Expression of oestrogen receptors was investigated by reve rse polymerase chain reaction. L-type calcium current was usually meas ured by the patch-clamp technique in whole-cell recording mode under s elective recording conditions, i.e. overlapping currents were blocked. One series of experiments was performed in perforated patch configura tion to avoid internal perfusion. 17 beta-Oestradiol inhibited L-type calcium current reversibly in all three species. At 10(-5) M, the inhi bition was 15-20%. This inhibition was independent of the sex and the species. A full concentration-response curve of 17 beta-oestradiol on basal L-type current was recorded from female guinea-pig myocytes. The inhibition increased from 2 % at 10(-7) M to about 30 % at 10(-4) M 1 7 beta-oestradiol. The values could be fitted by a sum of two sigmoida l functions with log EC50 values of -6.5 and -4.9 M and Hill slopes of 2.5 for both. The specificity of the 17 beta-oestradiol action was te sted by recording the L-type current in the presence of 17 alpha-oestr adiol and oestrone. 17 alpha-Oestradiol also inhibited the current, bu t with a maximal inhibition of only 17 %. The concentration-response c urve could be fitted by a single sigmoidal function (log EC50 -6.3 M; Hill slope 0.55). Oestrone did not influence the current at all. The d ecrease in L-type current after the application of 17 beta-oestradiol via a rapid perfusion system developed with a time constant of 3.4 s, which was in the same range as that for the influence of isoprenaline. The isoprenaline-stimulated L-type current was much more susceptible to the inhibition by 17 beta-oestradiol, i.e., in pre-stimulated cells (1) the inhibitory effect is significantly higher (e.g. at 10(-5) M, inhibition was 36.3 % compared with 11.2 % in untreated cells) and (2) an inhibitory effect can be seen with oestradiol concentrations as lo w as 10(-9) M. Although the concentrations needed to gain a calcium an tagonistic influence on the basal current were much too high to explai n a cardio-protective influence of oestrogens, the presence of oestrog en receptors in cardiac myocytes of all three species, together with t he shift in concentration dependence following pre-stimulation by isop renaline, suggest that myocytes are a potential target for oestrogen.