R. Meyer et al., RAPID MODULATION OF L-TYPE CALCIUM CURRENT BY ACUTELY APPLIED ESTROGENS IN ISOLATED CARDIAC MYOCYTES FROM HUMAN, GUINEA-PIG AND RAT, Experimental physiology, 83(3), 1998, pp. 305-321
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.