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K channel activation by nucleotide diphosphates and its inhibition by glibenclamide in vascular smooth muscle cells
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.tb13849.x
Subject(s) - intracellular , glibenclamide , extracellular , reversal potential , chemistry , biophysics , channel blocker , nucleotide , guanosine diphosphate , vascular smooth muscle , quinidine , patch clamp , stereochemistry , biochemistry , smooth muscle , endocrinology , guanine , biology , pharmacology , receptor , calcium , gene , diabetes mellitus , organic chemistry
1 Whole‐cell and inside‐out patch recordings were made from single smooth muscle cells that had been isolated enzymatically and mechanically from the rabbit portal vein. 2 In whole‐cells the inclusion in the recording pipette solution of nucleotide diphosphates (NDPs), but not tri‐ or monophosphates, induced a K‐current that developed gradually over 5 to 15 min. Intracellular 1 m m guanosine 5′‐diphosphate (GDP) induced a slowly developing outward K‐current at − 37 mV that reached a maximum on average of 72 ± 4 pA ( n = 40). Half maximal effect was estimated to occur with about 0.2 m m GDP. Except for ADP, other NDPs had comparable effects. At 0.1 m m , ADP was equivalent to GDP but at higher concentration ADP was less effective. ADP induced its maximum effect at 1 m m but had almost no effect at 10 m m . 3 In 14% of inside‐out patches exposed to 1 m m GDP at the intracellular surface, characteristic K channel activity was observed which showed long (> 1 s) bursts of openings separated by longer closed periods. The current‐voltage relationship for the channel was linear in a 60 m m :130 m m K‐gradient and the unitary conductance was 24 pS. 4 Glibenclamide applied via the extracellular solution was found to be a potent inhibitor of GDP‐induced K‐current ( I K(GDP) ) in the whole‐cell. The K d was 25 n m and the inhibition was fully reversible on wash‐out. 5 ( I K(GDP) ) was not evoked if Mg ions were absent from the pipette solution. In contrast the omission of extracellular Mg ions had no effect on outward or inward ( I K(GDP) ). 6 Inclusion of 1 m m ATP in the recording pipette solution reduced ( I K(GDP) ) and also attenuated its decline during long (25 min) recordings. 7 When perforated‐patch whole‐cell recording was used, metabolic poisoning with cyanide and 2‐deoxy‐ d ‐glucose induced a glibenclamide‐sensitive K‐current. This current was not observed when conventional whole‐cell recording was used. Possible reasons for this difference are discussed. 8 These K channels appear similar to ATP‐sensitive K channels but we refer to them as nucleotide diphosphate‐dependent K channels (K NDP ) to emphasise what seems to be a primary role for nucleotide diphosphates in their regulation.