Reduced cytosolic Ca2+ loading and improved cardiac function after cardioplegic cold storage of guinea pig isolated hearts

Background-Hypothermia is cardioprotective, but it causes Ca2+ loading and reduced function on rewarming. The aim was to associate changes in cytosoli c Ca2+ with function in intact hearts before, during, and after cold storag e with or without cardioplegia (CP). Methods and Results-Guinea pig hearts were initially perfused at 370 degree s C with Krebs-Ringer's (KR) solution tin mmol/L: Ca2+ 2.5, K+ 5,Mg2+ 2.4). One,group was perfused with CP solution (Ca2+ 2,5, K+ 18, Mg2+ 7.2) during cooling and storage at 3 degrees C for 4 hours; another was perfused with KR. LV pressure (LVP), dP/dt, O-2 consumption, and cardiac efficiency were monitored. Cytosolic phasic [Ca2+] was calculated from indo 1 fluorescence signals obtained at the LV free wall. Cooling with KR increased diastolic a nd phasic [Ca2+], whereas cooling with CP suppressed phasic [Ca2+] and redu ced the rise in diastolic [Ca2+]. Reperfusion with warm KR increased phasic [Ca2+] 86% more after CP at 20 minutes and did not increase diastolic [Ca2 +] at 60 minutes, compared with a 20% increase in phasic [Ca2+] after KR. D uring early and later reperfusion after CP, there was a 126% and 50% better return of LVP than after KR; during later reperfusion, O-2 consumption was 23% higher and cardiac efficiency was 38% higher after CP than after KR. Conclusions-CP decreases the rise in cardiac diastolic [Ca2+] observed duri ng cold storage in KR, Decreased diastolic [Ca2+] and increased systolic [C a2+] after CP improves function on reperfusion because of reduced Ca2+ load ing during and immediately after cold CP storage.