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

Summary A tightly-sealed cardiac sarcolemmal patch preparation of large diameter (10–16 m with 5–25 G 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 A/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 <0.1M internal free, calcium. Maximum exchange current density is >20 A/cm².Supported by a Grant-in-Aid and an Established Investigatorship of the American Heart Association.