| IntroductionAtrial fibrillation ( AF) is one of the most serious cardiac arrhythmia affecting patient's quality of life. The etiology is not fully understood and few therapies have been proved effective. Atrial fibrillation and its mechanism have been the frontier study in the heart surgery. The present studies have indicated that atrial fibrillation may alter the electrophysiological characteristic, which is " electrophysiologi-cal remodeling". These includes progressive shortening of effective refractory period ( ERP) and action potential duration ( APD ) , decreased ERP to heart rhythm and decreased conduction speed in atrium. Electrophysiological remodeling induced by AF is related to the modification of cellular membranous ionic channel in atrial myocytes. Transient outward potassium current ( Ito) and steady - state outward potassium current (Iksus)play an important role in the action potential repolarization in atrial myocytes. In this study, patch clamp technique was used to study the change of Ito and Ik3U3 in atrial miocytes with AF and to evaluate the ionic channel mechanism of atrial electrophysiological remodeling.Materials and methods1. Myocardium preparationMyocardial samples were taken from rheumatic valvular patients who were performed from Oct. 2001 to March 2002 in China Medical University Hospital. 11 patients with AF duration longer than 3 months were included in the AF group. Control group was 10 cases of valve replacement without AF. Myocardial sample was taken before cardioplegia and placed in cold Ca * - free cardioplegic solution bubbled with 100% oxygen and was transferred to lab for digestion quick-ly-2. Isolation of single atrial myocyteMyocardium sample was cut into small block of 1mm3 with fine scissors. Single myocyte was isolated with enzymatic dissociation techniques and the cells with best quality were collected and stored in KB solution (The above procedures were carried out at 37C with 100%O2)3. Recording of currentsA few drops of isolated myocytes were placed in bath of 1 cm3 on microscope. 5 min later, column -shaped myocytes with strong membranous reflection and clear were prepared of patch clamp. Verapamil and TEA were added in the bathing solution. Natrium current was deactivated with - 40mV holding potential. When whole cell recording finished, holding potential was set to -40mV, commanding potential was depolarized from - 60mV to + 60 mV, with step pulse at 10 mV, holding duration of 200 ms and stimulating interval of 3s. Time dependent Itoand Iksus were induced.4. Data processingRecorded current was analyzed with program of pCLAMPS. 5. lClampan,Clampex and Clampfit. Statistical analysis was performed with SPSS 10. 0. Data were expressed as means ?SD. Inter groups comparison was performed with student t test. When P is less than 0. 05, the difference was considered statically significant.Results1. Ito current intensityItowas recorded with holding potential of - 40 mV and commanding potential from - 60mV to + 60 mV with increased commanding potential, Itocurrent increased gradually and reached its peak value when commanding potential was + 60 mV. At various commanding potential, Itoin AF group was significantly lower than that in control group. With commanding potential of +60 mV, Ito was 160. 32±38. 25pA(n=21) and 512. 74 ±41.63 pA(n =18) in AF and control group. Itoin AF group was significantly reduced by 68. 73% (P < 0.01)2. Iksu9 current intensityAt various commanding potential, Iksus in AF group was lower than that in control group. With commanding potential of + 60 mV, Iksus in AF and control group was 502. 71 ?4. 97 pA(n=21) and 748.56±52.27 pA( n = 18) , respectively. Iksus in AF group was significantly reduced by 48.91% (P <0.01).DiscussionElectrophysiological remodeling of atrial myocytes induced by AF was one of the important characteristics in AF. The shortening of APD and ERP is related to the increased depolarization of membranous po-tential induced by K+ channel...
|
PDF Full Text Request