Abstract
1. The effect of 17 beta-oestradiol on cardiac cell contraction, inward Ca2+ current and intracellular free Ca2+ ([free Ca2+]i) was investigated in guinea-pig single, isolated ventricular myocytes. The changes of cell length were measured by use of a photodiode array, the voltage-clamp experiments were performed with a switch clamp system and [free Ca2+]i was measured with the Ca2+ indicator, Fura-2. 2. 17 beta-Oestradiol (10, 30 microM) caused a decrease in cell shortening at both 22 and 35 degrees C. This negative inotropic effect was accompanied by a decrease in action potential duration mainly brought about by a shortening of the plateau region of the action potential. 17 beta-Oestradiol (10, 30 microM) induced a similar decrease in cell shortening in voltage-clamped and current-clamped cells. 3. In Fura-2 loaded cells, 17 beta-oestradiol (10 and 30 microM) decreased systolic Fura-2 fluorescence to 72 +/- 7% and 47 +/- 4% (n = 6, P less than 0.001) of control respectively. 17 beta-Oestradiol (10 microM) had no significant effect on diastolic Fura-2 fluorescence, but at higher concentration (30 microM) induced a slight decrease in resting Fura-2 fluorescence. The effect of 17 beta-oestradiol was reversible after 1-2 min of washout of the steroid. 4. 17 beta-Oestradiol (10 and 30 microM) decreased the peak inward Ca2+ current (ICa), which was sensitive to [Ca2+]o, dihydropyridines and isoprenaline, to 59 +/- 3% and 39 +/- 5% (n = 7 approximately 9, P less than 0.01) respectively, without producing any significant change in the shape of the current-voltage relationship.(ABSTRACT TRUNCATED AT 250 WORDS)
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