Activation and inhibition of purified skeletal muscle calcium release channel by NO donors in single channel current recordings

The actions of the nitric oxide (NO) donors 1-hydroxy-2-oxo-3-(N-methyl-3-a minopropyl)-3 methyl-1-triazine (NOC-7): S-nitrosoacetylcysteine (CySNO) an d S-nitrosoglutathione (GSNO) on the purified calcium release channel (ryan odine receptor) of rabbit skeletal muscle were determined by single channel current recordings. In addition, the activation of the NO donor modulated calcium release channel by the sulfhydryl oxidizing organic mercurial compo und 4-(chloromercuri)phenylsulfonic acid (4-CMPS) was investigated. NOC-7 ( 0.1 and 0.3 mM) and CySNO (0.4 and O.S mM) increased the open probability ( P-o,) of the calcium release channel at activating calcium concentrations ( 20-100 mu M Ca2+) by 60-100%, with no effect on the current amplitude; this activation was abolished by the specific sulfhydryl reducing agent DTT. Hi gh concentrations of CySNO (1.6-2 mM) decreased P-o,. Activation by GSNO (1 mM) was observed in two thirds of the experiments, but 2 mM and 4 mM GSNO markedly reduced P-o, at activating Ca2+ (20-100 mu M). In contrast to 4-CM PS, NOC-7 or GSNO had no effect at subactivating: free Ca2+ (0.6 mu M). 4-C MPS further increased the open probability of NOC-7- or CySNO-stimulated ch annels and reversed transiently the reduced open probability of CySNO or GS NO inhibited channels at activating free Ca2+. High concentrations of GSNO did not prevent channel activation of 4-CMPS at subactivating free Ca2+. Th e NOC-7-, CySNO- or GSNO-modified channels were completely blocked by ruthe nium red. It is suggested that nitrosylation/oxidation of sulfhydryls by NO donors and oxidation of sulfhydryls by 4-CMPS affect different cysteine re sidues essential in the gating of the calcium release channel. (C) 1999 Els evier Science B.V. All rights reserved.