Properties of single chloride selective channel from sarcoplasmic reticulum

The behavior of single chloride channels in sarcoplasmic reticulum of rabbit and trout skeletal muscle was examined by fusing isolated vesicle fractions into planar lipid bilayers. The channel exhibited a full open state with a unit conductance of 65 pS (in 100 mM Cl^-) and several subconductance states with reversal potentials which were dependent on the chloride gradient across the bilayer. Open probability was 0.6–0.95 for membrane potentials ranging from-60 to+60 mV. The kinetic behaviour could be described by assuming one time constant for the fully conducting channel, and at least two time constants for the non-conducting channel. In the presence of methane sulfonate, sulfate and phosphate anions, a decrease in the unit current amplitude but not open time argued in favor of a competition between these anions and Cl^- at the transport site of the channel. Chloride channel activity was not affected by variations of Ca²⁺ concentration in both chambers or by the presence of Mg²⁺. Similarly, neither millimolar ATP nor the presence of the drugs taurine (up to 10 mM), lidocaine (2–40 M) or the calmodulin antagonist W7 (5–150 M), modified channel behavior. Finally, pH variations between 6.8 to 8 were without effect.Abbreviations DIDS 4,4-Diisothiocyanostilbene-2,2-disulfonic acid - EGTA Ethylene glycol bis-(-aminoethyl ether) N,N,N',N'-tetraacetic acid - HEPES N-2-Hydroxyethyl-piperazine-N'-2-ethane sulfonic acid - SR Sarcoplasmic reticulum - TRIS Tris(hydroxymethyl)aminomethane