The efficiency of heart protection with HTK or HTK-N depending on the type of ischemia

We investigated isolated guinea pig hearts (n = 121) in an ischemia/reperfusion model with the aim to compare the efficiency of the cardioplegic solution FMK with its novel replacement HTK-N. Following consolidation with Tyrode's solution, ischemia started either immediately or after preceding cardioplegia with HTK, HTK-N, or modified HTK enriched with Ca. Ischemia lasted either 80 min at 30 degrees C, or 360 min at 5 degrees C, or 81 min at 30 degrees C with intermittent cardioplegic perfusion. During ischemia we measured intracellular calcium (iCa(++)) and the time of gap junction uncoupling (t-in). During reperfusion we measured the re-establishment of cell coupling (t-ret), left ventricular developed pressure (LVDP), and heart rhythm (VC-RR). In 5 degrees C groups, iCa(++) at t-in was significantly higher than before ischemia, and longest t-in, shortest t-ret, and best VC-RR were observed after HTK-protection. Of all 30 degrees C groups, the intermittent group with modified HTK showed shortest t-ret, best VC-RR, and the highest LVDP. At 5 degrees C, HTK groups had higher LVDP than HTK-N groups, but not at 30 degrees C. The data suggest that the higher calcium level in the HTK-N solution improves reperfusion after short ischemia at 30 degrees C but for long lasting ischemia at 5 degrees C it is beneficial to use the HTK solution. (C) 2018 Elsevier B.V. All rights reserved.