Alterations in pore-forming subunits of adenosine triphosphate-sensitive potassium channels in pressure overload rat cardiomyocytes.

Abstract

Adenosine triphosphate (ATP)-sensitive potassium channels (KATP) link cellular metabolic state and electrical activity of cardiomyocytes. Pharmacological studies indicated the involvement of KATP in pressure overload-induced left ventricular hypertrophy, but the alteration of pore-forming subunits, Kir6.1 and Kir6.2, at membranes and subcellular fractions is unclear. The objective of this study was to investigate the changes in the distribution and levels of Kir6.1 and Kir6.2 in rat cardiomyocytes responding to chronic pressure overload. Male Wistar rats were separated into a sham-operated group (sham) and a pressure overload or transverse aortic constriction (TAC) group. Echocardiography was performed to assess cardiac structure and functions at the 4th month after operation. Ventricular cardiomyocytes in both groups were isolated and then subjected to extract protein into cytoplasm, organelle membrane, and plasma membrane fractions. Immunoblotting and immunohistochemistry techniques were performed to detect and measure Kir6.1 and Kir6.2 protein levels. Echocardiographic parameters showed left ventricular hypertrophy with hypercontractility in TAC rats. The immunoblotting showed the presence of Kir6.1 and Kir6.2 at plasma membranes and only Kir6.1 at organelle membranes. Significantly, Kir6.1 and Kir6.2 levels were decreased in the plasma membrane fraction of the TAC group (n = 8 and 6 for Kir6.1 and Kir6.2, respectively), whereas Kir6.1 in the organelle membrane fraction tended to be higher in TAC but did not reach statistical significance (n = 7). These results seemed to relate to a left ventricular immunohistochemistry study, which showed the trend of decreased staining of Kir6.1 and Kir6.2 in pressure overload left ventricular tissue. In conclusion, both Kir6.1 and Kir6.2 plasma membrane subunits were decreased significantly in pressure overload-induced left ventricular hypertrophy.