Diazoxide maintenance of myocyte volume and contractility during stress: evidence for a non-sarcolemmal K(ATP) channel location.
OBJECTIVE
Animal and human myocytes demonstrate significant swelling and reduced contractility during exposure to stress (metabolic inhibition, hyposmotic stress, or hyperkalemic cardioplegia), and these detrimental consequences may be inhibited by the addition of diazoxide (adenosine triphosphate-sensitive potassium channel opener) via an unknown mechanism. Both SUR1 and SUR2A subunits have been localized to the heart, and mouse sarcolemmal adenosine triphosphate-sensitive potassium channels are composed of SUR2A/Kir6.2 subunits in the ventricle and SUR1/Kir6.2 subunits in the atria. This study was performed to localize the mechanism of diazoxide by direct probing of sarcolemmal adenosine triphosphate-sensitive potassium channel current and by genetic deletion of channel subunits.


METHODS
Sarcolemmal adenosine triphosphate-sensitive potassium channel current was recorded in isolated wild-type ventricular mouse myocytes during exposure to Tyrode's solution, Tyrode's + 100 μmol/L diazoxide, hyperkalemic cardioplegia, cardioplegia + diazoxide, cardioplegia + 100 μmol/L pinacidil, or metabolic inhibition using whole-cell voltage clamp (N = 7-12 cells per group). Ventricular myocyte volume was measured from SUR1(-/-) and wild-type mice during exposure to control solution, hyperkalemic cardioplegia, or cardioplegia + 100 μmol/L diazoxide (N = 7-10 cells per group).


RESULTS
Diazoxide did not increase sarcolemmal adenosine triphosphate-sensitive potassium current in wild-type myocytes, although they demonstrated significant swelling during exposure to cardioplegia that was prevented by diazoxide. SUR1(-/-) myocytes also demonstrated significant swelling during exposure to cardioplegia, but this was not altered by diazoxide.


CONCLUSIONS
Diazoxide does not open the ventricular sarcolemmal adenosine triphosphate-sensitive potassium channel but provides volume homeostasis via an SUR1-dependent pathway in mouse ventricular myocytes, supporting a mechanism of action distinct from sarcolemmal adenosine triphosphate-sensitive potassium channel activation.
Sellitto
Angela D
AD
Division of Cardiothoracic Surgery, Department of Surgery, Washington University School of Medicine, St Louis, MO 63110, USA.
Maffit
Sara K
SK
Al-Dadah
Ashraf S
AS
Zhang
Haixia
H
Schuessler
Richard B
RB
Nichols
Colin G
CG
Lawton
Jennifer S
JS
D018528:ATP-Binding Cassette Transporters / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002314:Cardioplegic Solutions / Q000494:pharmacology; D002316:Cardiotonic Agents / Q000494:pharmacology*; D048429:Cell Size / Q000187:drug effects*; D003981:Diazoxide / Q000494:pharmacology*; D005260:Female; D006706:Homeostasis; D006947:Hyperkalemia / Q000378:metabolism; D054086:KATP Channels / Q000819:agonists* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D009997:Osmotic Pressure; D018408:Patch-Clamp Techniques; D020110:Pinacidil / Q000494:pharmacology; D024661:Potassium Channels, Inwardly Rectifying / Q000819:agonists* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D011955:Receptors, Drug / Q000819:agonists* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D012508:Sarcolemma / Q000187:drug effects* / Q000378:metabolism; D064233:Sulfonylurea Receptors
C577507:ABCC8 protein, human; C577510:ABCC9 protein, human; D018528:ATP-Binding Cassette Transporters; C577508:Abcc8 protein, mouse; C577511:Abcc9 protein, mouse; D002314:Cardioplegic Solutions; D002316:Cardiotonic Agents; D054086:KATP Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D020110:Pinacidil; D003981:Diazoxide
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