Potassium channels and preconditioning of isolated rabbit cardiomyocytes: effects of glyburide and pinacidil.
Calcium tolerant rabbit cardiomyocytes, isolated by collagenase perfusion, were preincubated for varying periods of time followed by resuspension in fresh media and centrifugation into an ischaemic pellet with restricted extracellular fluid. Pellets were incubated for 240 min under oil at 37 degrees C to mimic severe ischaemia. Time to onset of ischaemic contracture (rod to square transformation) and trypan blue permeability following resuspension in 85 mOSM media were monitored at sequential times. The protocol of Series 1 was a 5-10 min pre-incubation, immediately followed by ischaemic pelleting. Preincubation with pinacidil (50 microM) protected cells from ischaemic insult, but pinacidil added only into the ischaemic pellet did not protect. Protection was abolished by the protein kinase (PKC) inhibitors chelerythrine (10 microM) added with pinacidil and calphostin C (200nM) added only into the ischaemic pellet. Neither PKC inhibitor had an effect on injury of untreated ischaemic myocytes (data not shown). Series 2-5 were preconditioning protocols with a 10 min intervention period, followed by a 30 min oxygenated drug-free period, prior to ischaemic pelleting. In series 2 pinacidil protected cells from ischaemic insult and this protection was abolished when glyburide (10 microM) was present during preincubation, or during post-incubation and ischaemia. Glyburide only partially inhibited the protection when glyburide was added only into the ischaemic pellet. In Series 3, 8-sulfophenyltheophyline (SPT)(100 microM) or adenosine deaminase during preincubation, or SPT only added into the ischaemic pellet abolished pinacidil's protection. In Series 4, cardiomyocytes were ischaemically preconditioned by pelleting for 10 min followed by 30 min reoxygenation. Glyburide during initial ischaemic blocked protection, but when added during post incubation and into the final pellet protection was not reduced. In Series 5 8-cyclopentyl-1,3,dipropylxanthine (DPCPX) (10 microM) added into the final pellet abolished protection by pinacidil, but not protection following ischaemic preconditioning. In contrast to pinacidil, ischaemically preconditioned cells maintain protection in the presence of glyburide, indicating that: (1) pinacidil does not exactly mimic preconditioning and (2) ischaemically preconditioned cells do not require opened K+ATP channels for protection, although they appear to be important during initiation of the preconditioned state. It is hypothesized that pinacidil opening of K+ channels may facilitate induction of preconditioning.
Department of Veterans Affairs Medical Center, Johnson City, Tennessee, USA.
S C
SC
Armstrong
G S
GS
Liu
J M
JM
Downey
C E
CE
Ganote
D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D005905:Glyburide / Q000494:pharmacology*; D006146:Guanidines / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects / Q000502:physiology* / Q000503:physiopathology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007700:Kinetics; D017202:Myocardial Ischemia / Q000503:physiopathology* / Q000517:prevention & control; D020110:Pinacidil; D015221:Potassium Channels / Q000502:physiology*; D058915:Purinergic P1 Receptor Antagonists; D011817:Rabbits; D013997:Time Factors; D014665:Vasodilator Agents / Q000494:pharmacology*; D014970:Xanthines / Q000494:pharmacology
D006146:Guanidines; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D058915:Purinergic P1 Receptor Antagonists; D014665:Vasodilator Agents; D014970:Xanthines; D020110:Pinacidil; C051360:1,3-dipropyl-8-cyclopentylxanthine; D005905:Glyburide