Characterization of a chloride channel reconstituted from cardiac sarcoplasmic reticulum

We have characterized a voltage-sensitive chloride channel from cardiac sarcoplasmic reticulum (SR) following reconstitution of porcine heart SR into planar lipid bilayers. In 250 mm KCl, the channel had a main conductance level of 130 pS and exhibited two substrates of 61 and 154 pS. The channel was very selective for Cl^– over K⁺ or Na⁺ ( and ). It was permeable to several anions and displayed the following sequence of anion permeability: SCN^– > I^– > NO ₃ ^– Br^– > Cl^– > f^– > HCOO^–. Single-channel conductance saturated with increasing Cl^– concentrations (K _m= 900 mm and _max = 488 pS). Channel activity was voltage dependent, with an open probability ranging from 1.0 around 0 mV to 0.5 at +80 mV. From –20 to +80 mV, channel gating was time-independent. However, at voltages below –40 mV the channel entered a long-lasting closed state. Mean open times varied with voltage, from 340 msec at –20 mV to 6 msec at +80 mV, whereas closed times were unaffected. The channel was not Ca²⁺-dependent. Channel activity was blocked by disulfonic stilbenes, arylaminobenzoates, zinc, and cadmium. Single-channel conductance was sensitive to trans pH, ranging from 190 pS at pH 5.5 to 60 pS at pH 9.0. These characteristics are different from those previously described for Cl^– channels from skeletal or cardiac muscle SR.We thank Dr. Barry Pallotta for help with open and closed intervals analysis and Dr. Gerhard Meissner for his suggestions for the preparation of cardiac sarcoplasmic reticulum membranes. This work was supported by a grant from the National Institutes of Health to R.L.R. and a Student Grant-in-Aid from the American Heart Association, North Carolina affiliate to C.T. R.L.R. is an Established Investigator of the American Heart Association.