Effect of brief hypoxia on reperfusion arrhythmias and release of Ca²⁺ by rat heart homogenate blocked by ryanodine

Objectives: We previously reported that a brief period of hypoxic perfusion (BHP) prior to ischemia in rat hearts improved functional recovery upon reperfusion with reduced Ca²⁺ overload. The present study was designed to determine whether the effect of BHP would be associated with a reduction in reperfusion arrhythmias and a preservation of function of the sarcoplasmic reticulum (SR). Methods: Hearts were subjected to 40 min of global ischemia and 30 min of reperfusion after a 20 min period of oxygenated perfusion (oxygenated group: OG), or a 10 min period of oxygenation and 10 min of hypoxic perfusion (hypoxic group: HG). We evaluated the release of Ca²⁺ by SR blocked by ryanodine, the recovery of left ventricular function, and the reperfusion induced ventricular tachycardia/fibrillation (VT/VF). Results: Functional recovery improved and the incidence and duration of reperfusion VT/VF were reduced in HG. In HG the uptake of Ca²⁺ in SR decreased during ischemia, but this decrease was less than that in OG. However, recovery of Ca²⁺ uptake after reperfusion did not differ between groups. The release of Ca²⁺ by SR blocked by ryanodine was inhibited in HG throughout the ischemia-reperfusion sequence. Conclusions: Observations suggest that the benefits of BHP on recovery of function and reperfusion arrhythmias were associated with a decrease in release of Ca²⁺ by SR blocked by ryanodine.