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 cytosolic Ca2+ with function in intact hearts before, during, and after cold storage with or without cardioplegia (CP). Methods and Results—Guinea pig hearts were initially perfused at 37°C with Krebs-Ringer’s (KR) solution (in 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°C for 4 hours; another was perfused with KR. LV pressure (LVP), dP/dt, O2 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 and phasic [Ca2+], whereas cooling with CP suppressed phasic [Ca2+] and reduced 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, compare...