Modulation of the calmodulin-induced inhibition of sarcoplasmic reticulum calcium release channel (ryanodine receptor) by sulfhydryl oxidation in single channel current recordings and [3H]ryanodine binding

The modulation of the calmodulin-induced inhibition of the calcium release channel (ryanodine receptor) by two sulfhydryl oxidizing compounds, 4-(chloro-mercuri)phenyl-sulfonic acid (4-CMPS) and 4,4'-dithiodipyridine (4,4'-DTDP) was determined by single channel current recordings with the purified and reconstituted calcium release channel from rabbit skeletal muscle sarcoplasmic reticulum (HSR) and [H-3]ryanodine binding to HSR vesicles. 0.1 mu M CaM reduced the open probability (P-o) of the calcium release channel at maximally activating calcium concentrations (50-100 mu M) from 0.502 +/- 0.02 to 0.137 +/- 0.022 (n = 28), with no effect on unitary conductance. 4-CMPS (10-40 mu M) and 4,4'-DTDP (0.1-0.3 mM) induced a concentration dependent increase in P-o (> 0.9) and caused the appearance of longer open states. CaM shifted the activation of the calcium release channel by 4-CMPS or 4,4'-DTDP to higher concentrations in single channel recordings and [H-3]ryanodine binding. 40 mu M 4-CMPS induced a near maximal (P-o > 0.9) and 0.3 mM 4,4'-DTDP a submaximal (P-o = 0.74) channel opening in the presence of CaM, which was reversed by the specific sulfhydryl reducing agent DTT. Neither 4-CMPS nor 4,4'-DTDP affected Ca-[I-125]calmodulin binding to HSR. 1 mM MgCl2 reduced P-o from 0.53 to 0.075 and 20-40 mu M 4-CMPS induced a near maximal channel activation (P-o > 0.9). These results demonstrate that the inhibitory effect of CaM or magnesium in a physiological concentration is diminished or abolished at high concentrations of 4-CMPS or 4,4'-DTDP through oxidation of activating sulfhydryls on cysteine residues of the calcium release channel.