| Popis: |
The objective of this study was to investigate the mechanisms of increase in the efficacy of ATP-sensitive K+ channel (K-ATP) openings by hypo-osmotic stress. The whole-cell K-ATP currents (I-K,I-ATP) stimulated by 100 mu mol/L pinacidil, a K+ channel opening drug, were significantly augmented during hypo-osmotic stress (189 mOsmol/L) compared with normal conditions (303 mOsmol/L). The EC50 and E-max value for pinacidil-activated I-K,I-ATP (measured at 0 mV) was 154 mu mol/L and 844 pA, respectively, in normal solution and 16.6 mu mol/L and 1266 pA, respectively, in hypo-osmotic solution. Augmentation of I-K,I-ATP during hypo-osmotic stress was attenuated by wortmannin (50 mu mol/L), an inhibitor of phosphatidylinositol 3- and 4-kinases, but not by (i) phalloidin (30 mu mol/L), an actin filament stabilizer, (ii) the absence of Ca2+ from the internal and external solutions, and (iii) the presence of creatine phosphate (3 mmol/L), which affects creatine kinase regulation of the K-ATP channels. In the single-channel recordings, an inside-out patch was made after approximately 5 min exposure of the myocyte to hypo-osmotic solution. However, the IC50 value for ATP under such conditions was not different from that obtained in normal osmotic solution. In conclusion, hypo-osmotic stress could augment cardiac I-K,I-ATP through intracellular mechanisms involving the phosphatidylinositol kinase pathway. |
