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Nitric oxide and thiol reagent modulation of Ca 2+ ‐activated K + (BK Ca ) channels in myocytes of the guinea‐pig taenia caeci
Author(s) -
Lang R. J.,
Harvey J. R.,
McPhee G. J.,
Klemm M. F.
Publication year - 2000
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2000.00363.x
Subject(s) - depolarization , chemistry , membrane potential , nitric oxide , biophysics , bk channel , sodium nitroprusside , biochemistry , biology , organic chemistry
1 The modulation of large conductance Ca 2+ ‐activated K + (BK Ca ) channels by the nitric oxide (NO) donors S ‐nitroso‐L‐cysteine (NOCys) and sodium nitroprusside (SNP) and agents which oxidize or reduce reactive thiol groups were compared in excised inside‐out membrane patches of the guinea‐pig taenia caeci. 2 When the cytosolic side of excised patches was bathed in a physiological salt solution (PSS) containing 130 m m K + and 15 n m Ca 2+ , few BK Ca channel openings were recorded at potentials negative to 0 mV. However, the current amplitude and open probability ( NP o ) of these BK Ca channels increased with patch depolarization. A plot of ln( NP o ) against the membrane potential ( V ) fitted with a straight line revealed a voltage at half‐maximal activation ( V 0.5 ) of 9.4 mV and a slope ( K ) indicating an e‐fold increase in NP o with 12.9 mV depolarization. As the cytosolic Ca 2+ was raised to 150 n m , V 0.5 shifted 11.5 mV in the negative direction, with little change in K (13.1 mV). 3 NOCys (10 μ m ) and SNP (100 μ m ) transiently increased NP o 16‐ and 3.7‐fold, respectively, after a delay of 2–5 min. This increase in NP o was associated with an increase in the number of BK Ca channel openings evoked at positive potentials by ramped depolarizations (between −60 and +60 mV). Moreover, this NOCys‐induced increase in NP o was still evident in the presence of 1 H ‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ; 10 μ m ), the specific blocker of soluble guanylyl cyclase. 4 The sulfhydryl reducing agents dithiothreitol (DTT; 10 and 100 μ m ) and reduced glutathione (GSH; 1 m m ) also significantly increased NP o (at 0 mV) 7‐ to 9‐fold, as well as increasing the number of BK Ca channel openings evoked during ramped depolarizations. 5 Sulfhydryl oxidizing agents thimerosal (10 μ m ) and 4,4′‐dithiodipyridine (4,4DTDP; 10 μ m ) and the thiol‐specific alkylating agent N ‐ethylmaleimide (NEM; 1 m m ) significantly decreased NP o (at 0 mV) to 40–50 % of control values after 5–10 min. Ramped depolarizations to +100 mV evoked relatively few BK Ca channel openings. 6 The effects of thimerosal on NP o were readily reversed by DTT, while the effects of NOCys were prevented by NEM. 7 It was concluded that both redox modulation and nitrothiosylation of cysteine groups on the cytosolic surface of the α subunit of the BK Ca channel protein can alter channel gating.