Sodium (2‐sulfonatoethyl) methanethiosulfonate prevents S ‐nitroso‐ L ‐cysteine activation of Ca 2+ ‐activated K + (BK Ca ) channels in myocytes of the guinea‐pig taenia caeca

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. In membrane patches bathed in a low Ca 2+ (15 n M ) 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 μ M for 2–5 min) such that 5–15 open BK Ca channels were evident. MTSEA (2.5 m M ) decreased, while MTSES (2.5 m M ) 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. MTSET (2.5 m M ) increased N.P o (at 0 mV) and voltage‐dependently decreased BK Ca current amplitudes in a manner readily reversed upon washout. Pre‐exposure of excised membrane patches to MTSES or N ‐ethylmaleimide (NEM 1 m M ), a specific alkylating agent of cysteine sulfhydryls, but not MTSEA or MTSET, prevented the excitatory actions of NOCys (10 μ M ). 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 α subunit that have an accessible water interface.British Journal of Pharmacology (2003) 139 , 1153–1163. doi: 10.1038/sj.bjp.0705349