Inhibition of sarcoplasmic reticulum calcium release reduces myocardial stunning

Recent findings indicate that ischemia/reperfusion (IR) is associated with phospholipase C (PLC)-induced inositol 1,4,5-triphosphate production, as well as abnormal sarcoplasmic reticulum (SR) Ca2+ release. Therefore, we hypothesized that increased SR Ca2+ release may contribute to Ca2+ overload and myocardial stunning. Neomycin (NEO) was used to inhibit PLC, and sodium dantrolene (DAN) was used to inhibit myocardial SR Ca2+ release. The purposes of this study were (1) to determine if PLC inhibition would reduce IR-induced ventricular dysfunction, (2) to examine ventricular function during inhibition of SR Ca2+ release prior to ischemia, and (3) to examine the influence of SR Ca2+ release inhibition on post-IR ventricular function. Left ventricular developed pressure (DP) and +/- dP/dt of isolated crystalloid perfused rat heart (Langendorff apparatus) paced at 350 bpm were compared before and after global IR (38 degrees C, 20 min I, 40 min R) to assess functional recovery. PLC was inhibited with NEO (10 microM x 5 min prior to ischemia), and SR Ca2+ release was retarded with DAN (12.5 microM) in 0.05% DMSO (vehicle) infused for 3 min via the aortic cannula 13 min prior to ischemia. No effect on DP was observed during NEO or DAN infusion. NEO and DAN pretreatment each improved recovery of DP (% recovery +/- SEM) following IR: control, 46.5 +/- 5.1%; NEO + IR, 71.0 +/- 6.3%,* vehicle + IR, 44.4 +/- 2.9%; DAN + IR, 71.0 +/- 4.7%, *, # (*P < 0.05 vs control IR, #P < 0.05 vs vehicle + IR, ANOVA, Scheffe F test, n = 5 all groups). We conclude that SR Ca2+ release during IR contributes to myocardial stunning.