Voltage-gated cation conductance channel from fragmented sarcoplasmic reticulum: steady-state electrical properties.

The interaction of fragmented sarcoplasmic reticulum (SR) with an artificial planar phospholipid membrane under conditions known to induce fusion of phospholipid vesicles raises the conductance of the planar bilayer by several orders of magnitude. Measurements of steady-state electrical properties of bilayers thus modified by SR show that two types of conductance pathways are present. One is a voltage-independent pathway which may be somewhat anion-selective. The other is a voltage-gated ionophore showing selectivity to small monovalent cations. This latter ionophore is fully oriented within the artificial bilayer and is inhibited asymmetrically by divalent cations. It is also inhibited below pH6. The ionophore displays single-channel conductance fluctuations between two states. "open" and "closed", with an open-state conductance of 1.4 x 10-10 mho in 0.1 M K+. The physiological function of this ionophore is unknown.