RESUMEN
AIM: [MgCl(2)] and [CaCl(2)] may modify the cardioprotective effects of hyperkalemic cardioplegia (CP). We changed [MgCl(2)] and [CaCl(2)] in a CP solution to examine their effects on [Ca(2+)]i transients and cardiac function before and after global normothermic ischemia. METHODS: After stabilization and loading of indo 1-AM in Kreb's solution (KR), each heart was perfused with either KR or 1 of 4 CP solutions before 37 degrees C, 30 min ischemia followed by reperfusion with KR. The KR solution contained, in mM, 4.5 KCl, 2.4 MgCl(2) and 2.5 CaCl(2); the CP solutions had in addition to 18 KCl: CP 1 (control CP): 2.4 MgCl(2), 2.5 CaCl(2); CP 2: 7.2 MgCl(2), 2.5 CaCl(2); CP 3, 7.2 MgCl(2), 1.25 CaCl(2); CP 4: 2.4 MgCl(2), 1.25 CaCl(2). RESULTS: In the KR group [Ca(2+)]i markedly increased on early reperfusion while functional return (LVP, dLVP/dt((max and min))) was much reduced; each CP group led to reduced [Ca(2+)]i loading and improved function. The rates of cytosolic Ca(2+) fluxes (d[Ca(2+)]/dt(max) and d[Ca(2+)]/dt(min)) increased significantly compared to baseline in the KR group, but were mostly suppressed in the CP groups, and d[Ca(2+)]/dt(min) was lower after CP 4 compared to CP 1 on reperfusion. At 60 min reperfusion, LVP area to [Ca(2+)] area and cardiac efficiency to phasic [Ca(2+)] relationships were shifted after KR, but not after CP 1-4. With similar functional recovery, [Ca(2+)] transient and [Ca(2+)] area were significantly lower after CP 4 than after CP 1. CONCLUSION: Increasing [MgCl(2)] (CP 2 and 3) did not improve cardiac function or reduce Ca(2+) transients on reperfusion better than the other CP groups, but reducing [CaCl(2)] (CP 3 and 4) was more effective in reducing [Ca(2+)] transients on reperfusion after global ischemia.