Steady-State and Post-Rest Potentiation ofTriggered Activity in Ventricular Muscleof Healthy vs. Myopathic Hamsters

• Main Authors: Jin-Hua Li, 李金樺
• Other Authors: 林正一
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/55122418132886731774

碩士 === 國防醫學院 === 生理學研究所 === 93 === Introduction The hereditary cardiomyopathic strain of the Syrain hamster (Bio 14.6) had been extensively used as an experimental model for the study of cardiomyopathy and heart failure (HF). It was assumed that, because of the inherited defects in the cytosolic calcium (Ca2+ i) reuptake process in the sarcoplasmic reticulum (SR), the myopathic myocytes would prone to develop Ca2+ i overload and the subsequent triggered arrhythmia. However, paradoxically, part of our previous experiments revealed that the myopathic hamsters had a lower incidence of reentrant atrial tachyarrhythmias and a smaller transient inward current (Iti) after prolonged depolarizing pulses (＞1000 ms) in concomitant with a longer APD and a reduced transient outward k+ current (Ito) in ventricular myocytes. Aims The aims of the present experiment were: (1) to study the ventricular muscles and cardiomyocytes from healthy and cardiomyopathic hamsters under conditions of intracellular calcium overload (perfusion with high [Ca]o-low [K]o solution or after repeated electrical pacing); (2) to examine the genesis of ventricular arrhythmias in the absence or presence of insulin, a polypeptide known to modulate intracellular calcium ([Ca2+]i) and increase contractile function of myopathic hamsters. Material and Methods 1. Preparation of hamster ventricular tissues : Animals (35-40 week-old) were anesthetized with an intreperitoneal injection of sodium pentobarbital (50 mg/kg). Papillary muscle obtained from left ventricle and perfused in vitro at 37℃. Steady-state (2 Hz) and post-rest (20s) action potentials were recorded by microelectrode techniques and twitch force by a transducer. 2. Isolation of ventricular myocytes: Male myopathic Syrian hamsters (Bio 14.6, 52-60 week-old) and healthy hamsters were anesthetized with pentobarbital and the heart quickly removed and immersed in HEPES-Tyrode solution. The hearts were perfused in a retrograde manner via polyethylene tube connected through the aorta and left ventricule into the atrium. The free end of the polyethylene tubing was connected to a Langendorff perfusion column for perfusion with oxygenated HEPES-Tyrode solution at 37℃. The perfusate was replaced with oxygenated Ca2+-free HEPES-Tyrode solution, then was replaced with containing collagenase (1 mg/ml) and protease (0.01 mg/ml) finally. The piece of tissue was cut into fine pieces and gently shaken in 20 ml of high-K storage solution until single cardiomyocytes were obtained. 3. Electrophysiology study: The isolated cells were placed in a 1-ml chamber mounted on the stage of an inverted microscope and superfused (at 3 ml/min) with extra-cellular solution appropriate to each patch-clamp experiment. Results 1. Ventricular papillary muscle obtained from 35-40 week-old myopathic hamsters (vs. those from healthy hamsters) are prone to develop signs of calcium overload: delayed afterdepolarization (DAD) and post-rest triggered arrhythmias in the presence of high-[Ca2+]o l o w - [ K + ] o p e r f u s a t e . 2. In ventricular myocytes isolated from 52-60 week-old myopathic hamsters, all preparations (n=6) generate transient inward currents (Iti) after repeated (up to 20 times) depolarizing pulses (from -40 to +40 mV for 500 ms every sec). In healthy preparations, only 2 of 7 m y o c y t e s develop Iti and the Iti are smaller in size. 3. Insulin (1 µM), a polypeptide known to enhance Ca2+ influx and induce positive inotropic response in myocardial cells, exaggerates DAD and Iti but does not increase inward rectifier K+ currents (IK1) in preparations from healthy hamsters. In myopathic ventricular muscles, insulin increases (to a lesser extent) the DAD but may increase or decrease Iti in myopathic myocytes due to difference in the age of animals and individual variation. Conclusions 1. With the experimental protocols adopted in the present study (repeated depolarizing pulses, post-rest potentiation of triggered actitivity, etc.), it has been demonstrated that preparations from myopathic hamsters are prone to develop triggered arrhythmias as compared to the healthy control. 2. Further experiments are required to clarify the discrepancies in results between ventricular tissues and cardiomyocytes.