ATP sensitive K+ channel may be involved in the protective effects of preconditioning in isolated guinea pig cardiomyocytes

Objective To develop a cellular model of preconditioning by a brief period of hypoxia in isolated guinea pig cardiomyocytes and to determine whether o r not an ATP sensitive K+(K-ATP) channel is involved in ischemic preconditi oning. Methods Single myocytes were isolated from the ventricle of adult guinea pi gs. The experimental chamber allowed the cells to be exposed to low O-2 pre ssure. During hypoxic preconditioning, the cells were equilibrated with nor maxic solution for 10 minutes and then exposed to hypoxia for 5 minutes, fo llowed by 10 minutes of reoxygenation. The cells were then subjected to 20 - 180 minutes of hypoxia and reoxygenation. Ionic currents were studied wit h the patch clamp technique in whole-cell and cell-attached configurations. Results A 5-minute hypoxic preconditioning offered a significant protection from cell injury in subsequent hypoxia-reoxygenation. After a latency of m ore than 15 minutes, hypoxia induced a time-independent outward K+ current which could be blocked by 5 mu mol/L glibenclamide. At 10 mV, the current i ncreased from 78 +/- 15 pA to 1581 +/- 153 pA ( P < 0.01, n = 18). However, the latency to develop K-ATP channel currents (I-KATP) was greatly shorten ed in preconditioned cells, and the current was increased acceleratively. A t 10 mV, the current more than 4 nA was recorded in preconditioning cells. In the single channel recordings, the time interval from the first channel opening to maximum opening was also markedly abbreviated in preconditioned cells. Conclusion Isolated guinea pig cardiomyocytes can be preconditioned with a brief period of hypoxia. This hypoxic preconditioning may modify the K-ATP channel, and make the channel open more readily during the second hypoxia.