The Influences Of Rosiglitazone On L-type Calcium Current (I_CaL) Of Ventricular Myocytes In Healthy And Diabetic Rabbits During Imitation Of Ischemia-reperfusion

Objective: There may be a common pathogenesis on both diabetic cardiomyopathyand coronary atherosclerotic heart disease (CHD). The endothelial dysfunction whichis caused by insulin resistance (IR), oxidative stress directly triggered byhyperglycemia, alters endothelium dependent vascular relaxation through interactionwith deficiency synthesis of NO. So that atherosclerosis became easy due to a seriesof reactions. It was claimed that there is a high ratio of cardiac myocytes necrosis inpatients with diabetes according to autopsy reports. And it is easy to be found out thatdiabetic patients undergoing consistent damages of residue living cells are notneglectable compared with the healthy ones. The present evidences demonstrated thatischemia preconditioning (IP) exist in diabetic, therefore diabetic cardiomyopathy as adefinition of dependent disease is well accepted by us. The peroxisome proliferatorsactivated receptors (PPARs) are a family of ligand activated transcription factorswithin the broad nuclear receptor superfamily. PPAR_γ, because of an adipose enrichednuclear receptor, also express in heart. It plays a great role in myocardial infarctionarea after ischemia-repurfusion, although the mechanism is still unknown. Manystudies pointed out that rosiglitazone may have a reverse effect on oxidative stessbesides its contribution to lowing blood glucose levels. It also keeps nomalendothelial function and improving ionic currents of vascular smooth muscles. (i.e.L-type calcium current). There may be the relation ship between rosiglitazone andheart disease protection. At present, there is still no study focus on rosiglitazone'seffect on ion currents during oxidative stress. This study aims at providing a newmethord of ischemia-reperfusion protection, a new electophysiology evidence ofrosiglitazone, and more benefits on patients with cardiovascular disease especially insubjects with disbetes.Methords: To establish the models of diabetes, mesoxalylurea drug solution wasejected intravenously, we measured fast glucose before ejection, 2 and 7 days afterdrug ejection (fast glucose should reach at a level higher than 10 mmol/L). Singlecardial myocytes were isolated from the ventricles of both normal and diabetic adultrabbit (immediately survival rate nearly 70%-90%, cellls should live more than 12h),As most patch clamp experiments, we use the pattern of voltage clamp by whole cell protocol to record calcium ionic current in different groups (include: normal group,diabetic group, normal group with rosiglitazone administration, diabetic group withrosiglitazone administration). The same protocol was studied in the conditions ofmimic ischemia reperfusion (5min of equilibration with normal extracellular solutionand then following 5 min ofperfusion with mimic ischemic solution).Results:1) It was showed that at 2nd and 7th day fast glucose (before 7.832±1.506mmol/L, at 2nd dayl 7.761±7.101mmol/L and at 7th day 20.638±9.003mmol/L) haveapparent differences with that before ejection of mesoxalylurea significantly (P＜0.05).And fast insulin at 2nd and at 7th day after drug ejection (before 23.454±9.215mmol/L,at 2nd day 22.686±8.939mmol/L and at 7th day 21.651±11.912mmol/L) have nodifferences with that before ejection of mesoxalylurea (P＞0.05).2) L-type calcium ionic current (I_CaL) curves are recorded separately at thebaseline, 5min and at 10min (the extracellular bath solution are mimic physicalperfusate with or without rosiglitazone, ischemic perfusate with or without rosiglita-zone), There was no differences of I_CaL between normal group(-8.618±3.878pA/pF)and diabetic group(-7.773±1.805 pA/pF, P=0.27). There were differences of I_CaL inall moments within these groups respectively (P＜0.05), which were administratedaccording to the methords before, including normal (baseline -8.826±2.306 pA/pF,after 5min-4.167±1.886 pA/pF, after 10min-5.539±1.628pA/pF) and diabetes withrosiglitazone group (baseline -8.842±1.978 pA/pF, after 05min -4.966±1.154pA/pF,after 10min -3.891±1.064pA/pF), ischemic group (baseline -8.223±1.553pA/pF, after5min-5,784±1.745 pA/pF, after 10min-3.958±0.992pA/pF), DM ischemic group(baseline-7.229±2.024 pA/pF, after 5min -6.110±1.621pA/pF, after 10min -4.775±1.204pA/pF), ischemic group with rosiglitazone administration (baseline-7.499±1.904pA/pF, after 5min -5.944±2.224 pA/pF, after lOmin -5.059±1.947pA/pF) andDM ischemic group with rosiglitazone administration (baseline -8.099±1.823pA/pF,after 5min -6.634±1.674pA/pF, after 10 min 5.349±1.520pA/pF).3) I_CaL curves were recorded separately. There was no differences of I_CaL at 5minand 10min within the six groups (P＞0.05)., including normal and diabetes with rosiglitazone group, ischemic group, DM ischemic group, ischemic and DM ischemicgroup with rosiglitazone administrationConclusion:1. The cardiocytes which are sent to carrying out experiment of patch clamp areisolated from both diabetic and nomal rabbits' ventricular myocardium. The similaritybetween healthy and ill ones indicate that diabetes can do no harm to cardiocytesalone.2. After imitating ischemia-reperfusion damage, changes of calcium ioniccurrents are the same as that of rosiglitazone. It is showed no benefits of ischemia-reperfusion on ICaL. Rosiglitazone takes after it.3. Effects of rosiglitazone on the heart were not attributed to diabetes. It may beexplained that rosiglitazone impacts on myocardial cells directly, suggesting a newmechanism of rosiglitazone.4. Diabetes caused by alloxan is different from type-1 and type-2 diabetesmellitus, therefore diabetes which is made by alloxan is less of insulin resistance. Wecan make better use of this diabetic model in estimating myocardiocyte damagementcaused by hyperglycemia.