Protective action of 17β-estradiol in cardiac cells:: Implications for hyperkalemic cardioplegia

Background Hyperkalemic cardioplegic solutions effectively arrest the heart, but may also induce intracellular Ca2+ loading and cellular hypercontracture, which could contribute to ventricular dysfunction associated with global surgical ischemia. Recently, it has been proposed that 17 beta-estradiol may possess protective properties in the ischemic myocardium. The purpose of the present study was to examine the action of 17 beta-estradiol on cardiac cells exposed to hyperkalemic stress. Methods. Single ventricular cardiomyocytes, a preparation devoid of vascular and neuronal elements, were isolated from guinea pig hearts, loaded with a Ca2+-sensitive fluorescent probe, and imaged by digital epifluorescent microscopy. The emitted fluorescence of the probe, a measure of intracellular Ca2+ concentration, and cell length were simultaneously recorded during hyperkalemic challenge, in the absence or presence of 17 beta-estradiol. Results. In control cardiomyocytes, the cytosolic concentration of Ca2+ was 138 +/- II nmol/L and cell length 93 +/- 11 mu m. Exposure to high Kf (+16 mmol/L KCI) significantly increased cytosolic Ca2+ to 2,191 +/- 187 nmol/L (p < 0.001), and produced cell shortening (length at 39 +/- 5 mu m; p < 0.001). 17 beta-Estradiol (10 mu mol/L) acutely prevented high Kf to induce either intracellular Ca2+ loading (144 +/- 13 nmol/L, p < 0.001) or hypercontracture (91 +/- 10 mu m, p < 0.001). Tamoxifen (10 mu mol/L), an antiestrogen, abolished the protective effect of 17 beta-estradiol. Conclusions. We conclude that 17 beta-estradiol prevents hyperkalemia-induced Ca2+ loading and hypercontracture through a direct and tamoxifen-sensitive action in cardiomyocytes. This study raises the possibility that 17 beta-estradiol should be considered as a cardioprotective adjunct toward a safer hyperkalemic cardioplegia. (C) 1998 by The Society of Thoracic Surgeons.