CHARACTERIZATION OF A CHLORIDE CHANNEL RECONSTITUTED FROM CARDIAC SARCOPLASMIC-RETICULUM

We have characterized a voltage-sensitive chloride channel from cardia c sarcoplasmic reticulum (SR) following reconstitution of porcine hear t 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 15 4 pS. The channel was very selective for Cl- over K+ or Na+ (P-K+/P-Cl - = 0.012 and P-Na+/P-Cl- similar to 0.040). It was permeable to sever al anions and displayed the following sequence of anion permeability: SCN- > I- > NO3- similar to Br- > Cl- > F- HCOO-. Single-channel condu ctance saturated with increasing Cl- concentrations (K-m = 900 mM and gamma(max) = 488 pS). Channel activity was voltage dependent, with an open probability ranging from similar to 1.0 around 0 mV to similar to 0.5 at +80 mV. From -20 to +80 mV, channel gating was time-independen t. However, at voltages below -40 mV the channel entered a long-lastin g closed state. Mean open times varied with voltage, from similar to 3 40 msec at -20 mV to similar 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 ca dmium. Single-channel conductance was sensitive to trans pH, ranging f rom similar to 190 pS at pH 5.5 to similar to 60 pS at pH 9.0. These c haracteristics are different from those previously described for Cl- c hannels from skeletal or cardiac muscle SR.