Detection of K⁺ and Cl⁻ channels from calf cardiac sarcolemma in planar lipid bilayer membranes

Abstract

The ionic currents underlying the cardiac action potential are believed to be much more complex than those in nerve^1,2. During the cardiac action potential, various membrane channels control the flow of K⁺, Na⁺, Ca²⁺ and Cl⁻ across the sarcolemma of cardiac muscle cells^2–7. Thus, it has become increasingly clear that a detailed knowledge of the mechanisms that activate (or inactivate) heart channels is required to understand cardiac excitability^8,9. We report here the use of planar lipid bilayer techniques to detect and characterize K⁺ and Cl⁻ channels in purified heart sarcolemma membrane vesicles. We have identified four different types of channel on the basis of their selectivity, conductance and gating kinetics. We present in some detail the properties of a K⁺ channel and a Cl⁻ channel. We have tentatively identified the K⁺ channel with the i_x, type of current found in Purkinje¹⁰, myocardial ventricular¹¹ and atrial¹² fibres. The chloride channel might be related to the transient chloride current found in Purkinje fibres^5,6,13.