Anti-ischemic effects of the potassium channel activators pinacidil and cromakalim and the reversal of these effects with the potassium channel blocker glyburide.

The direct cardioprotective efficacy of the potassium channel activators pinacidil and cromakalim was determined in isolated globally ischemic rat hearts. Isolated buffer-perfused rat hearts were subjected to 25 min of ischemia followed by 30 min of reperfusion. These hearts were pretreated with 1 to 100 microM pinacidil, 1 to 7 microM cromakalim or vehicle. Pinacidil resulted in significant improvements in reperfusion function and cardiac compliance, though it did not significantly reduce lactate dehydrogenase release at any concentration. The protective effects of pinacidil were greatest at a 10 microns concentration and were slightly diminished at higher concentrations (30 and 100 microns). Although not affecting the severity of ischemia alone, 10 microM glyburide (potassium channel blocker) completely reversed the protective effects of pinacidil on reperfusion function and compliance. Cromakalim (7 microM) resulted in a greater than 50% improvement in reperfusion function and compliance and unlike pinacidil significantly reduced lactate dehydrogenase release by approximately 50%. At 1 microM, glyburide alone did not significantly affect the severity of ischemia but reversed the protective effects of cromakalim. Not only did glyburide reverse the protective effects of cromakalim, it resulted in a worsening of ischemia compared to vehicle, an effect not seen with glyburide alone. Thus, both pinacidil and cromakalim appear to have direct cardioprotective efficacy, though some differences between them may be possible. The mechanism of their protective effects appears to be via potassium channel opening as the potassium channel blocker glyburide reverses the protective effect of these compounds. Intracellular electrophysiological studies showed that ischemia-induced depolarization was reversed with cromakalim, which increased the resting potential nearly back to preischemic levels.(ABSTRACT TRUNCATED AT 250 WORDS)