Protective Effect Of A Non - Depolarizing Cardiac Arrest Fluid On Vascular Endothelium And Its Mechanism

Background and Objective:Cardioplegia is the key to cardioprotection in cardiac surgery, but in addition to cardiomyocytes, cardioplegic solutions are also in direct contact with coronary vascuLar endothelium, and the effects on vascuLar endothelium also affect cardioprotective effects. Among many functions of endothelium, the reguLation of vascuLar tone is particuLarly important, as it is related to coronary perfusion, and good perfusion is a key factor to ensure perfect heart function. The endothelium plays a reguLatory role in vascuLar tone through releasing muLtiple vasoactive substances that act on vascuLar smooth muscle cells. Among those, three relaxing factors:nitric oxide (NO), prostaglandin (PGI2) and endothelium-derived hyperpolarizing factor (EDHF) have been identified to contribute to endothelium-dependent relaxation. NO and EDHF are two main mechanisms. Our previous studies found that the EDHF-mediated relaxation may be reduced after exposure to hyperkalemic cardioplegia, thus affecting the cardioprotective effect. Therefore, it is meaningfuL to study the protective effects of different cardioplegic solutions on coronary endothelium. This study was designed to explore the protective effects and mechanisms of a non-depolarizing cardioplegia (NDP) on coronary endothelial function.First, the study was designed to investigate the protective effects of NDP solution on EDHF-mediated relaxation of porcine coronary arteries in comparision with Krebs-Helenseit(KH) solution, St.Thomas (ST) solution, Histidine-Tryptophan-Ketoglutarate (HTK) solution after vascuLar rings were incubated with these solutions at37℃for1hour or at4℃for10hour. Then, the study was aimed to explore the mechanism of potassium channels in protective effects of NDP solution on EDHF-mediated vasodilation. The potassium channels involved in the study mainly includes calcium-activated potassium (KCa) channels, inward rectifier potassium (Kir) channels, ATP-sensitive potassium channels (KATP), voltage-dependent potassium (Kv) channels.Methods: Part1:Due to different preservation solutions used in different groups, the rings were divided into four groups:control (CON) group、St.Thomas (ST) group、 Histidine-Tryptophan-Ketoglutarate (HTK) group、NDP group. Rings from porcine coronary arteries were studied in the organ chamber. After equilibration, the rings were incubated with Krebs-Helenseit solution in CON group, St.Thomas solution in ST group, Histidine-tryptophan-ketoglutarate solution in HTK group, non-depolarizing solution in NDP group at37℃for1hour or at4℃for10hour. Then Pre-contraction tone induced by prostaglandin F2a U46619and endothelium-dependent relaxation tone induced by bradykinin was measured in the presence of indomethacin (Indo) and N-nitro-L-arginine (L-NNA).Part2:Rings from porcine coronary arteries were studied in the organ chamber, after equilibration for1hour, the control group rings were incubated with Indo and L-NNA, the other groups were incubated with Indo, L-NNA and different potassium channel blockers. Since KCa can be divided into three types:Large-Conductance KCa (BKCa), Intermediate-Conductance KCa (IKCa) and Small-Conductance KCa (SKCa), these blockers are iberiotoxin (a specific blocker of BKCa channels), charybdotoxin (a blocker of BKCa channels and IKCa channels), apamin (a specific blocker of SKCa channels), barium chloride (BaCl2, a blocker of Kir channels), Glibenclamide (a blocker of KATP channels),4-Aminopyridine (4-AP, a specific blocker Kv channels). Then Pre-contraction tone induced by prostaglandin F2a U46619and endothelium-dependent relaxation tone induced by bradykinin was measured in the presence of Indo and L-NNA with/without different calcium-activated potassium channel blockers.ResuLts:Part1:After incubation with different solutions at37℃for1hour, the EDHF-mediated relaxation induced by bradykinin was much higher in the NDP group (74.79%±2.26%) than in the HTK group (51.32%±7.75%), CON group (24.03%±2.83%) and ST group (16.20%±2.26%); after incubation with different solutions at4℃for10hour, the EDHF-mediated relaxation induced by bradykinin was much higher in the NDP group (70.35%±5.58%) than in the HTK group (61.53%±5.04%), CON group (28.11%±3.77%) and ST group (20.16%±3.02%), but statistical analysis showed no significant difference between NDP group and HTK group.Part2:Compared with the control group (65.71%±5.60%), EDHF-mediated endothelium-dependent relaxation induced by bradykinin was significantly decreased in Charybdotoxin group (23.57%±3.46%), Charybdotoxin+Apamin group (8.01%±2.32%), while the relaxation of Apamin group (59.52%±4.85%) was not statistically significant in comparision with the control group (65.71%±5.60%); Compared with the control group (71.88%±6.23%), EDHF-mediated endothelium-dependent relaxation induced by bradykinin was significantly decreased in the Iberiotoxin group (25.67%±1.86%); Compared with the control group (63.43%±7.71%), EDHF-mediated endothelium-dependent relaxation induced by bradykinin was significantly decreased in the BaCl2group (9.34%±1.37%); Compared with the control group (51.41%±5.49%), EDHF-mediated endothelium-dependent relaxation induced by bradykinin was partly inhibited in the Glibenclamide group (37.05%±5.32%); EDHF-mediated endothelium-dependent relaxation induced by bradykinin was63.43±7.71%and54.31±3.35%respectively in the control group and Glibenclamide group, but statistical analysis showed no significant difference between NDP group and HTK group.Conclusions:1. NDP solution and HTK solution provides superior endothelium protective effect in comparision with ST solution at37℃for1hour, and NDP solution is better than HTK solution.2. NDP solution and HTK solution provides superior endothelium protective effect in comparision with ST and HTK solution at4℃for10hour, but tne effect of NDP solution is similar to HTK solution.3. BKca channels, SKca channels, Kir channels and KATP channels play a role in the protective effects of NDP solution on EDHF-mediated vasodilation. Among these channels, BKCa and SKCa channels act in a coordinated manner. However, Kv channels do not play a role.