ATP-sensitive potassium channels in neonatal and adult rabbit ventricular myocytes.

The properties of the ATP-sensitive potassium (KATP) current were studied in freshly isolated rabbit ventricular myocytes using the patch clamp technique. Removing ATP from the bath (intracellular) solution activated a large K+ conductance in patches from neonatal cells with properties similar to those of KATP channels in other preparations. In membrane patches from neonatal ventricular myocytes, the density of KATP channels was higher than the density of inwardly rectifying K+ channels and the mean patch KATP current was approximately 10 times that of the inwardly rectifying K+ current, at a patch membrane potential of -60 mV. Glibenclamide (10 microM) in the bath solution decreased the number of functional KATP channels, the open-state probability, and the mean patch membrane current. The single-channel conductance of the KATP channel was dependent on the external K+ concentration, and the relationship between channel conductance and external K+ concentration was fit by an exponential equation. In addition, the voltage dependence, channel density, and open-state probability of this channel were compared between neonatal and adult isolated ventricular myocytes. The single-channel conductance and channel density of the KATP channel in neonatal myocytes were significantly smaller than in adult cells. These results suggest that age-related changes occur in the properties of KATP channels.