Fluorescence-based functional assay for sarcolemmal ATP-sensitive potassium channel activation in cultured neonatal rat ventricular myocytes.

INTRODUCTION: Activation of ATP-sensitive K+ channels (K(ATP)) has been shown to induce ischemic preconditioning that serves as a protective mechanism in the heart. A high throughput assay for identifying K(ATP) channel openers would therefore be desirable.
METHODS: We describe a cell-based 96-well format fluorescence assay using bis-(1,3-dibutylbarbituric acid)trimethine oxonol (DiBAC4(3)) to evaluate membrane potential changes evoked by K(ATP) channel openers and blockers in cultured neonatal rat ventricular myocytes.
RESULTS: Pinacidil and its analog P1075 (N-cyano-N'-(1,1-dimethylpropyl)-N"-3-pyridylguanidine), ZD6169 (N-(4-benzoylphenyl)-3,3,3,-trifluoro-2-hydroxy-2-methyl propionamide), and the enantiomers of cromakalim evoked concentration-dependent decreases in DiBAC4(3) fluorescence responses. Pretreatment with the K(ATP) channel blocker, glyburide attenuated opener-evoked decreases in fluorescence responses in a concentration-dependent manner. The rank order potency of openers in cardiac myocytes correlated well, but showed 6-10-fold higher potency in activating vascular smooth muscle K(ATP) channels in A10 cells. DISCUSSION: Our studies demonstrate that the pharmacological modulation of sarcolemmal K(ATP) channels can be readily assessed in a high throughput manner by measuring glyburide-sensitive fluorescence changes in cardiac ventricular myocytes.