title: Calcium modulation of vascular smooth muscle ATP-sensitive K(+) channels: role of protein phosphatase-2B.
abstract: ATP-sensitive K(+) (K(ATP)) channels are broadly distributed in the vasculature and regulate arterial tone. These channels are inhibited by intracellular ATP ([ATP](i)) and vasoconstrictor agents and can be activated by vasodilators. It is widely assumed that K(ATP) channels are insensitive to Ca(2+), although regulation has not been examined in the intact cell where cytosolic regulatory processes may be important. Thus we investigated the effects of Ca(2+) on whole-cell K(ATP) current in rat aortic smooth muscle cells recorded in a physiological [ATP](i) and K(+) gradient. Under control recording conditions, cells had a resting potential of approximately -40 mV when bathed in 1.8 mmol/L Ca(2+). The K(ATP) channel inhibitor glibenclamide caused membrane depolarization (9 mV) and inhibited a small, time-independent background current. Reducing [ATP](i) from 3 to 0.1 mmol/L hyperpolarized cells to approximately -60 mV and increased glibenclamide-sensitive current by 2- to 4-fold. Similar effects were observed when Ca(2+) levels were decreased either externally or internally by increasing EGTA from 1 to 10 mmol/L. Dialysis with solutions containing different free [Ca(2+)](i) showed that K(ATP) current was maximally activated at 10 nmol/L [Ca(2+)](i) and almost totally inhibited at 300 nmol/L. Moreover, under control conditions, when rat aortic smooth muscle cells were dialyzed with either cyclosporin A, FK-506, or calcineurin autoinhibitory peptide (structurally unrelated inhibitors of Ca(2+)-dependent protein phosphatase, type 2B), glibenclamide-sensitive currents were large and the resting potential was hyperpolarized by approximately 20 to 25 mV. We report for the first time that K(ATP) channels can be modulated by Ca(2+) at physiological [ATP](i) and conclude that modulation occurs via protein phosphatase type 2B.
authors.affiliation: Centre for Clinical Pharmacology, Department of Medicine, University College London, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Wilson
authors.forename: R I
authors.initials: RI
authors.lastname: Jabr
authors.forename: L H
authors.initials: LH
authors.lastname: Clapp
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D019703:Calcineurin / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D019806:Cromakalim / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D065095:Calcineurin Inhibitors; D004791:Enzyme Inhibitors; D015221:Potassium Channels; D014665:Vasodilator Agents; D019806:Cromakalim; D000255:Adenosine Triphosphate; D019703:Calcineurin; D011188:Potassium; D005905:Glyburide; D002118:Calcium