17β-estradiol regulates expression of KATP channels in heart-derived H9c2 cells

Objectives The main objective of the present study was to establish whether 17beta-estradiol (E2) regulates expression of cardiac adenosine triphosphate-sensitive potassium (K-ATP) channel. Background Based on our previous studies that demonstrate gender-specific differences in sarcolemmal K-ATP channels, we have hypothesized that the main estrogen, E2, may regulate expression of cardiac K-ATP channels. Methods Reverse transcription-polymerase chain reaction (RT-PCR) using primers specific for Kir6.2 and sulfonylurea receptor 2A (SUR2A) subunits was performed on total ribonucleic acid (RNA) from rat embryonic heart-derived H9c2 cells. Immunoprecipitation and Western blotting using anti-Kir6.2 and anti-SUR2A antibodies was done on membrane fraction of H9c2 cells. Whole cell electrophysiology and digital epifluorescent Ca2+ imaging were performed on living H9c2 cells. All experiments were done in cells incubated 24 h with or without 100 nM E2. Results The RT-PCR revealed higher levels of SUR2A, but not Kir6.2, messenger RNA (mRNA) in E2-treated, relative to untreated, cells. Increase of the level of only the SUR2A subunit could change the number of sarcolemmal KA(TP) channels only if the Kir6.2 is in excess over SUR2A. Indeed, RT-PCR analysis demonstrated considerably lower levels of SUR2A mRNA compared with Kir6.2 mRNA. Significantly higher levels of both Kir6.2 and SUR2A protein subunits were found in the membrane fraction of E2-treated cells compared with untreated ones, and the density of current evoked by pinacidil (100 muM), a K-ATP channel opener, was significantly higher in E2-treated compared with untreated cells. To test the effect of E2 on cellular response to hypoxia-reoxygenation, we have measured on-line, intracellular concentration of Ca2+ in H9c2 cells exposed to hypoxia-reoxygenation. Intracellular Ca2+ loading induced by hypoxia-reoxygenation was significantly decreased by treatment with E2. This E2-mediated protection was inhibited by HMR 1098 (30 muM), but not by 5-hydroxydecanoate (50 muM). Conclusions In conclusion, this study has demonstrated that E2 increases levels of SUR2A subunit, stimulates K-ATP channel formation and protects cardiac cells from hypoxia-reoxygenation.