Effects Of Sevoflurane Preconditioning And Postconditioning On Reperfusion Arrhythmia Of Isolated Rat Hearts And Electrophysiology Of Ventricular Myocytes

Objective:1. To investigate the effects of sevoflurane preconditioning and postconditioning on reperfusion arrhythmia.2. To investigate the effects of sevoflurane preconditioning and postconditioning on electrophysiological characteristics of action potential, L-type calcium current (ICa, L), fast sodium current (INa) and transient outward potassium current (Ito) from ventricular myocytes.3. To compare the effects of sevoflurane preconditioning and postconditioning on reperfusion arrhythmia and electrophysiology of ion channelsMethods:1. Isolated SD rat hearts were balanced with Krebs-Henseleit (KH) solution for15min and then randomly assigned to one of the following4groups (n=10):(1)Time Control (TC) group, which was perfused with KH solution for75min;(2) Ischemia/reperfusion (I/R) group, which was subjected to25min of global ischemia, followed by30min of reperfusion with KH solution;(3) sevoflurane preconditioning (SpreC) group, which was preconditioned with3%sevoflurane for15min before global ischemia and reperfusion;(4) sevoflurane postconditioning (SpostC) group, which was postconditioned with3%sevoflurane for15min at the onset of reperfusion. Hemodynamics, cardiac troponin I levels, infarct size, reperfusion arrhythmia, intracellular calcium and reactive oxygen species levels were compared among groups.2. Isolated SD rat hearts were used to implement the ischemia/reperfusion protocol. The grouping was similar with part1. After reperfusion, isolated epicardial ventricular myocytes were dissociated enzymatically for patch clamp studies. To investigate the effects of SpreC and SpostC on electrophysiology of ventricular myocytes, action potential amplitude, resting membrane potential, action potential duration, ICa, L,INa and Ito (Current-Voltage curve, steady-state activation curve, steady-state inactivation curve, and recovery curve) were recorded with the whole cell patch clamp techniques.Results:1. Compared with the I/R group, SpreC and SpostC increased left ventricular developed pressure,±dp/dt, and heart rate, and decreased left ventricular end-diastolic pressure (P<0.05). SpreC and SpostC decreased cardiac troponin Ⅰ levels, reduced infarct size and attenuated reperfusion arrhythmia, manifested by decreased numbers of ventricular premature beats, lowed incidence of ventricular fibrillation, shortened duration of ventricular tachycardia and ventricular fibrillation, and lowed reperfusion arrhythmia score (P<0.05). SpreC and SpostC decreased intracellular calcium and reactive oxygen species levels (P<0.05). There was no significant difference between SpreC and SpostC in the above parameters (P>0.05).2.(1) Action potential. Compared with the TC group, I/R injury decreased action potential amplitude, elevated resting membrane potential, and shortened action potential duration (P<0.05). Compared with the I/R group, SpreC and SpostC increased action potential amplitude, lowered resting membrane potential, and prolonged action potential duration (P<0.05).(2)ICa,L.Compared with the TC group, I/R lowered the peak density of ICa, L, decreased half inactivation voltage, moved the steady-inactivation curve to the left and increased recovery time constant (P<0.05). Compared with the I/R group, SpreC and SpostC increased the peak density of ICa, L, increased half inactivation voltage, moved steady-inactivation curve to the right, and decreased recovery time constant (P<0.05).(3)INa.Compared with the TC group, I/R injury decreased the peak density of INa and the slope factor of steady-inactivation curve (P<0.05). Compared with the I/R group, SpreC and SpostC increased the peak density of INa and the slope factor k of steady-inactivation curve (P<0.05).(4)Ito. Compared with the TC group, I/R injury decreased the peak density of Ito, increased half activation voltage and half inactivation voltage, and moved the steady-activation curve and steady-inactivation curve to the right (P<0.05). Compared with the I/R group, SpreC and SpostC increased the peak density of Ito, decreased half inactivation voltage, and moved the steady-inactivation curves to the left (P<0.05). There was no significant difference between SpreC and SpostC in the parameters about action potential, Ica, L, INa, and Ito (P>0.05).Conclusion:1. SpreC and SpostC could protect the isolated rat heart against ischemia/reperfusion injury, manifested by improved hemodynamics, reduced myocardial injury, decreased infarct size, and improved reperfusion arrhythmia, which may be involved in decreased intracellular calcium and reactive oxygen species levels.2.(1) SpreC and SpostC could attenuate the depressing effect of I/R injury on action potential.(2) SpreC and SpostC could increase the peak density of Ica, l, accelerate the inactivation of Ica, L and slow the recovery of Ica, L, which is useful to prolong the action potential duration of the I/R injured myocytes, resulting in lowered dispersion of repolarization. In addition, the effect of SpreC and SpostC on Ica, L contribute to the maintaining of calcium homeostasis.(3) SpreC and SpostC elevate the peak density of INa, which could increase the Vmax of phase0in action potential and accelerate the impulse conduction. The above effects are of preventive effect on excitatory reentrant arrhythmia.(4) SpreC and SpostC could increase the peak density, lower half inactivation voltage, and accelerate the inactivation of Ito from I/R injured ventricular myocytes. These changes may attenuate the negative effect of I/R injury on action potential, reduce the dispersion of repolarization, reduce the Ito-mediated phase2reentry and lower the incidence of after depolarization. These effects are contributed to attenuated reperfusion arrhythmia.3. There is no significant difference between SpreC and SpostC in hemodynamic recovery, cTnI release, infarct size and reperfusion arrhythmia from I/R injured heart. There is no significant difference between SpreC and SpostC in the characteristics of action potential, Ica, L, INa and Ito from I/R insulted ventricular myocytes.