| IntroductionAtrial fibrillation ( AF) is the most prevalent sustained tachyarrhythmia and is a threatening disease to human health. Nowadays, the mechanism of AF is still undefined. A great deal of clinical studies and epidemiology research showed that atrial electrid remodeling is very important to occurrence and maintain of AF. Therefore, the inhibiting channel remodeling is studing focus.Atrial electrid remodeling can effect the repolarization currents. Potassium currents are the major outward currents of action potential repolarization, so potassium currents are important investigate target of AF. IKur is a subtype of Ik which expresses in atrial myocytes, but very little or not in ventricle myocytes. The treatment to AF may be compeletely separated from leading arrhythmia by slective inhibition of IKur. Therefore, high - powered specific inhibitor of IKur plays a significant role in antiarrhythmia.Chitin is extensively consisted in shell of shellfish, insect and other nonver-tebrate. Chitosan is the product of chitin shucking off acetyl . The studying showed that chitosan could cure infection, tumor and prevent hypertension, as well as antiarrhythmia. The previous studies had observed that CMCS could inhibit Ik in single isolated ventricle myocyte of guinea pig. The studying observed firstly the effect of CMCS on IKur in rat single atrial myocyte using patch - clamp technique in order to further reveal ionic mechanism to atrial arrhythmia.Methods1. Isolation of single atrial cellMale of female Wistar rats ( 200 - 250g) , supplied by Laboratory AnimalCenter of CMU, were anesthetized by ip injection of a dose (20 mg kg -1 ) of Pentobarbital Sodium. Heart were mounted on a Langendorff apparatus and were retrogradely perfused via the aorta with oxygenate at 37 C. Singal myocyte was i-solated with enzymatic dissociation techniques and the cells with best quality and quantity and was collected and stored in KB at 4 C for Ih before use.2. Whole cell reording IKur with patch - clamp methodIsolated atrial cells were placed in a 1. 5ml chamber on invert microscope. Only relaxed, spindle - shaped cells were used for experiments. Single cell was voltage - clamped, and membrane currents were measured using the whole - cell configuration of the patch - clamp technique. IKur was recorded as described previously : The stimulating protocol was holding potential - 60 mV, stimulating potential -40 mV to +50 mV, step pulse +10 mV, duration 1200 ms, stimulating interval 3 s and stimulating frequency 2 Hz, preceded by a 200 ms pre-pulse to + 30 mV; the distance between the prepulse and test pulse was 20 ms. We observe the changes of currents and record at all times after I Kur stabilize 1 -2min. '3. Statistics analysisAll data analysis was performed with pclamp 5.5.1 software. IKur was measured as the amplitude of the current remaining at the end of the test pulse relative to the zero current level. Data were presented as x s. Statistical significance was assessed using a paired t - test and p <0. 05 was considered significant.ResultsWhen holding potential was 60 mV and stimulating potential was + 50 mV, IKur reduced from (1.8 0.7) and (2.0 0.6) nA by (14 6)% (n = 12, P <0.01) and (23 3)% (n=7, P<0. 01), respectively, after 1 and 2 g L -1 CMCS were added to extracellular solution. The changes of IKur were consistent with this under other commanding potentials. With the increases of stimulating frequency and commanding potential, no significant change of IKur was seen, which suggested CMCS inhibited IKur in a voltage - independency and frequency- independency manner.Discussion1. Patch -clamp technique and its application in cardiovascular studies Patch - clamp technique is a technique that reports molecular activity ofsingal of several ion channel by recording currents. To physiological research method of cell and molecular level, this technique is a revolutionary...
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