The measurement of cardiac membrane channels following their incorporation into phospholipid bilayers.

This chapter describes the basic properties of integral membrane channels from both cardiac sarcoplasmic reticulum and sarcolemma. Channels are studied, under voltage-clamp conditions, following their incorporation into planar phospholipid bilayers by fusion of isolated native membrane vesicles with preformed membranes. The rate of fusion of vesicles may be influenced by a number of factors including divalent cations and negatively charged phospholipids in the preformed bilayer. Mammalian cardiac sarcoplasmic reticulum contains a monovalent cation selective channel with a single-channel conductance of approximately 150 pico-Siemens in the presence of symmetrical solutions of 500 mM K+ at holding potentials ranging from -60 to +60 mV. The probability of the channel being in the open state is high at positive holding potentials and low at negative holding potentials. Mammalian cardiac sarcolemma contains at least three K+-selective channels and one Cl(-)-selective channel.