Abstract 15729: Subcellular Distribution of ATP-Sensitive K+ Channels in Ventricular Myocytes
Ventricular ATP-sensitive potassium (KATP) channels link intracellular energy metabolism to membrane excitability and contractility. Our recent proteomics data identified ventricular cell end-to-end junction proteins, including plakoglobin (PKG) and plakophilin-2 (PKP2), as interacting proteins of the KATP channel. It is likely that the association of KATP channel subunits with these proteins translates to an uneven subcellular distribution of KATP channels within a cardiac myocyte. Co-immunoprecipitation experiments confirmed the physical interaction of KATP channel subunits with PKP2 and PKG. Immunostaining experiments demonstrated that KATP channel subunits (Kir6.2, SUR2A and SUR2B) are expressed at higher density at the intercalated disk region in isolated cardiac myocytes and cryosections of mouse and rat hearts. Patch clamp experiments were performed to determine the local KATP channel density (mean patch current). A large patch-to-patch variation was observed, suggestive of KATP channel clustering. Overall, our results demonstrated a significantly larger KATP channel current density in patches obtained from ends of cardiomyocytes in comparison to the middle of the cell. Although the KATP channel unitary conductance did not differ between these two locations, the KATP channel from the cell end is less sensitive to exogenous ATP. In contrast, MgADP activated the two channel populations to the same degree. We next investigated KATP channel density in PKP2 knockout mice. The whole-cell KATP channel current density (activated by metabolic inhibition) was less in ventricular myocytes from PKP2-/+ mice compared to WT mice, despite comparable levels of the Kir6.2 protein in both groups. The larger KATP channel current in the cell end seen in myocytes from WT mice was not observed in PKP2-/+ mice. Channel unitary conductance and nucleotide sensitivities are not different between two channel populations in PKP2-/+ myocytes. Together, the higher density of KATP channels at the intercalated disk region of ventricular myocytes and its lower sensitivity to inhibitory ATP suggest a novel role for the KATP channel at the cellular junctions (and possibility electrical coupling between cells) during cardiac ischemia.
- © 2012 by American Heart Association, Inc.