Identification of two types of ATP-sensitive K+ channels in rat ventricular myocytes

The ATP-sensitive K+ (KATP) channels are known to provide a functional linkage between the electrical activity of the cell membrane and metabolism. Two types of inwardly rectifying K+ channel subunits (i.e., Kir6.1 and Kir6.2) with which sulfonylurea receptors are associated were reported to constitute the KATP channels. In this study, we provide evidence to show two types of KATP channels with different biophysical properties functionally expressed in isolated rat ventricular myocytes. Using patch–clamp technique, we found that single-channel conductance for the different two types of KATP channels in these cells was 57 and 21 pS. The kinetic properties, including mean open time and bursting kinetics, did not differ between these two types of KATP channels. Diazoxide only activated the small-conductance KATP channel, while pinacidil and dinitrophenol stimulated both channels. Both of these KATP channels were sensitive to block by glibenclamide. Additionally, western blotting, immunochemistry, and RT-PCR revealed two types of Kir6.X channels, i.e., Kir6.1 and Kir6.2, in rat ventricular myocytes. Single-cell Ca2+ imaging also revealed that similar to dinitrophenol, diazoxide reduced the concentration of intracellular Ca2+. The present results suggest that these two types of KATP channels may functionally be related to the activity of heart cells.