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Single channel and whole‐cell K‐currents evoked by levcromakalim in smooth muscle cells from the rabbit portal vein
Author(s) -
Beech D.J.,
Zhang H.,
Nakao K.,
Bolton T.B.
Publication year - 1993
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1993.tb13850.x
Subject(s) - pipette , glibenclamide , intracellular , chemistry , biophysics , tetraethylammonium , analytical chemistry (journal) , biochemistry , endocrinology , potassium , biology , chromatography , organic chemistry , diabetes mellitus
1 Single channel and whole‐cell current recordings were made from single smooth muscle cells isolated from the rabbit portal vein. 2 Application of 10 μ m levcromakalim ((−)‐Ckm) to single cells held with pipettes containing 1 m m GDP induced a K‐current ( I K(Ckm) ) which occurred in addition to the current caused by GDP alone ( I K(GDP) ) and averaged 135 pA at − 37 mV. We have investigated whether the same K channels underlie the GDP‐ and Ckm‐induced K‐currents. 3 If 1 m m GDP was in the pipette but Mg ions were omitted the effect of GDP was absent and I K(Ckm) averaged only 10 pA, suggesting that the action of (−)‐Ckm was Mg‐dependent. 4 Intracellular ATP was not observed to have much effect on I K(‐Ckm) . Loading of cells with 10 m m ATP from the recording pipette had no significant effect and flash photolysis of caged‐ATP loaded into cells from the pipette, estimated to release about 1 m m free ATP, also had no effect on I K(‐Ckm) . 5 Bath‐applied glibenclamide inhibited I K(‐Ckm) with an IC 50 of 200 n m , a value 8 times higher than that found for inhibition of I K(GDP) . The delayed rectifier K‐current ( I K(DR) ) was also inhibited by glibenclamide but at higher concentrations (IC 50 100 μ m ). Bath‐applied tetraethylammonium ions (TEA) inhibited I K(‐Ckm) and I K(GDP) to the same extent (IC 50 about 7 m m ). 6 In inside‐out patch recordings (−)‐Ckm (10 μ m ) applied to the intracellular surface of the membrane potentiated the opening of K channels already stimulated by 1 m m GDP and all of the channel activity was abolished by 10 μ m glibenclamide. The unitary conductance of the channels was 24 pS in a 60 m m : 130 m m K‐gradient. 7 We suggest that (−)‐Ckm may hyperpolarize and relax smooth muscle cells by opening K NDP , a class of small conductance K channels that are related to the ATP‐sensitive K channels seen in other tissues.