Identification of ATP-sensitive Potassium Channel in Frog Ventricular Myocytes

Abstract.

ATP-sensitive potassium channels were found in frog ventricular myocytes using the inside-out patch-clamp technique. The channel was selectively permeable to K⁺. Single-channel conductance was 32.6 pS at 3.0 mm of [K⁺] _o and 132 mm [K⁺] _i and 77.3 pS at 114 mm [K⁺] _o and 132 mm [K⁺] _i . ATP did not affect single-channel conductance. The open probability of the channel was decreased by intracellular application of ATP in both the presence and absence of 2 mm MgCl₂. The coexistence of Mg²⁺ with ATP shifts the dose-response curve for the open probability of ATP-sensitive K⁺ channel against ATP rightward. The shift of the curve indicates that Mg-ATP is less effective than free ATP in inhibiting the channel. An open-time histogram was fitted by a single exponential function with a time constant of 1.63 ± 0.17 msec (n= 5) in an ATP-free medium. Mean open time (1.57 ± 0.10 msec; n= 5) was not altered but the inter-burst time (closed time between bursts) lengthened in 10 μm ATP.