Sulfhydryl modification inhibits K+ (M) current with kinetics close to acetylcholine in rodent NG108-15 cells.
The effects of sulfhydryl reagents on M-type voltage-dependent potassium currents (IK(M)) were examined in NG108-15 cells transformed to express ml muscarinic acetylcholine receptors (mAChRs), a NGPM1-27 clone. Focal application of glutathione at millimolar concentrations dissolved in acidic solutions caused a transient inward current in NGPM1-27 cells at holding potentials of -30mV, associated with an inhibition of IK(M). The glutathione-induced response was mimicked by cysteine. These effects were also reproduced by superfusion with micromolar concentrations of HgCl2, AgNO3, N-methylmaleimide and p-chloromercuribenzoic acid (pCMB), agents which target protein thiols. Glutathione, HgCl2, AgNO3 and pCMB inhibited the peak conductance of IK(M) without shifting the half activating voltage (V1/2), which was comparable to the acetylcholine (ACh)-induced response. The voltage dependence of time constants for IK(M) deactivation in sulfhydryl reagent-, ACh- and non-treated cells resembled, but differed from that in Ba(2+)-treated cells. These results reveal that there is an accessible cysteine moiety, but not a disulfide bond, either on the M channel protein itself or on a protein directly involved in agonist-M channel coupling.
Egorova
A
A
Department of Biophysics, Kanazawa University School of Medicine, Japan.
Hoshi
N
N
Knijnik
R
R
Shahidullah
M
M
Hashii
M
M
Noda
M
M
Higashida
H
H
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D003545:Cysteine / Q000494:pharmacology; D005910:Glioma; D005978:Glutathione / Q000031:analogs & derivatives / Q000494:pharmacology; D019803:Glutathione Disulfide; D005998:Glycine / Q000494:pharmacology; D006822:Hybrid Cells; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008627:Mercuric Chloride / Q000494:pharmacology; D051379:Mice; D009447:Neuroblastoma; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D012835:Silver Nitrate / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D014162:Transfection
D015221:Potassium Channels; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D013439:Sulfhydryl Reagents; D008627:Mercuric Chloride; D012835:Silver Nitrate; D005978:Glutathione; D003545:Cysteine; D000109:Acetylcholine; D005998:Glycine; D019803:Glutathione Disulfide