Giant excised cardiac sarcolemmal membrane patches: sodium and sodium-calcium exchange currents

Abstract

A tightly-sealed cardiac sarcolemmal patch preparation of large diameter (10–16 μm with 5–25 GΩ seals) has been developed to study regulation of selected electrogenic mechanisms. Formation of a large readily accessible membrane surface area is achieved by incubating freshly isolated myocytes in a high KCl/zero calcium solution, which promotes separation of sarcolemma from myofilaments. The formation of large-diameter, high resistance seals is facilitated by depositing a neutral hydrocarbon film on electrode tips. Sodium currents in excised patches are stable for patch life-times of 15–40 min with peak current densities of 120 to 350 μA/cm². Outward sodium-calcium exchange current is identified by its specific dependence on external calcium and internal sodium, inhibition by cobalt and dichlorobenzamil, and activation by 20 μA/cm².