Sodium (2-sulfonatoethyl) methanethiosulfonate prevents S-nitroso-L-cysteine activation of Ca2+-activated K+ (BKCa) channels in myocytes of the guinea-pig taenia caeca.
1. The modulation of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels by the nitric oxide (NO(.)) donor, S-nitroso-L-cysteine (NOCys) and three sulfhydryl-specific methanethiosulfonate (MTS) reagents, positively charged 2-aminoethyl MTS hydrobromide (MTSEA C(3)H(9)NO(2)S(2)HBr) and [2-(trimethylammonium) ethyl MTS bromide (MTSET C(6)H(16)NO(2)S(2)Br), and negatively charged sodium (2-sulfonatoethyl) MTS (MTSES C(3)H(7)O(5)S(3)Na) were compared in excised inside-out membrane patches of the guinea-pig taenia caeca. 2. In membrane patches bathed in a low Ca(2+) (15 nM) high K(+) physiological salt solution, 1-3 BK(Ca) channels opened with a low probability (N.P(o)) of 0.019+/-0.011 at 0 mV. N.P(o) readily increased with membrane depolarization, raised Ca(2+) concentration or upon the addition of NOCys (10 micro M for 2-5 min) such that 5-15 open BK(Ca) channels were evident. 3. MTSEA (2.5 mM) decreased, while MTSES (2.5 mM) increased N.P(o) (at 0 mV) and the number of open BK(Ca) channels at positive potentials. These changes in channel activity remained after a prolonged washout of these two MTS reagents. 4. MTSET (2.5 mM) increased N.P(o) (at 0 mV) and voltage-dependently decreased BK(Ca) current amplitudes in a manner readily reversed upon washout. 5. Pre-exposure of excised membrane patches to MTSES or N-ethylmaleimide (NEM 1 mM), a specific alkylating agent of cysteine sulfhydryls, but not MTSEA or MTSET, prevented the excitatory actions of NOCys (10 micro M). 6. It was concluded that NOCys-evoked increases in BK(Ca) channel activity occur via the S-nitrosylation of cysteine residues within basic regions of the channel alpha subunit that have an accessible water interface.
Lang
Richard J
RJ
Department of Physiology, Monash University, Clayton, Victoria 3800, Australia. rick.lang@med.monash.edu.au
Harvey
John R
JR
Mulholland
Emily L
EL
D000818:Animals; D002432:Cecum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D003545:Cysteine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008698:Mesylates / Q000494:pharmacology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors* / Q000378:metabolism; D026403:S-Nitrosothiols / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D008698:Mesylates; D024681:Potassium Channels, Calcium-Activated; D026403:S-Nitrosothiols; C109153:(2-sulfonatoethyl)methanethiosulfonate; C021315:S-nitrosocysteine; D003545:Cysteine