EFFECT OF PRECONDITIONING ON RYANODINE-SENSITIVE CA2-RETICULUM OF RAT-HEART( RELEASE FROM SARCOPLASMIC)

The effect of varying the number of preconditioning (PC) episodes on t he recovery of cardiac function and on the function of the sarcoplasmi c reticulum (SR) was investigated to determine the correlation between the effect of PC and SR function. Isolated rat hearts were subjected to zero to three 5-min episodes of global ischemia with intermittent p erfusion (PC0-PC3) followed by 25 min of ischemia (I) and 30 min of re perfusion. The left ventricular (LV) pressure and SR Ca-45(2+) uptake in the absence or presence of ryanodine were then measured. The increa se in LV end-diastolic pressure and the incidence and duration of vent ricular tachyarrhythmias during reperfusion decreased. The recovery of LV developed pressure, LV dP/dt(max) and dP/dt(min), increased as the number of episodes of PC increased. The rates of SR Ca-45(2+) uptake after PC and after reperfusion were lower in PC3 than in PC0. Converse ly, the rate of Ca-45(2+) uptake after I did not differ between PC0 an d PC3. The ryanodine-sensitive Ca2+ release increased after I, and add itional increases were observed during reperfusion in PC0, whereas the release after I and reperfusion decreased progressively in PC3. These observations show that the beneficial effects of PC are associated wi th a decrease in ryanodine-sensitive SR Ca2+ release.