| Background and aimCalcitonin gene-related peptide (CGRP) is the most potent endogenous vessel dilator found by now. CGRP and its receptors distribute widely in nervous system and caidiovascular system. CGRP plays an important role in regulating cardiovascular system. CGRP will decrease or increase compensatorily in the progress of some diseases, such as hypertension, coronary heart disease, and heart failure. The number of hypertensive patient is increasing year by year. Such kinds of atrial tachyarryhthmias as atrial tachycardias and atrial fibrillation may probably occur in hypertensive hearts. It was manifested that remarkable electrical remodeling existed in the atria with fibrillation, and electrical remodeling was closely related with the change of L type Ca:+ channel, transient outward K+ channel, Na+ channel, and so on. So we assumed that there exist certain changes of these channels in hypertensive atria and CGRP may play a role in electrical remodeling of atria. It is difficult to investigate the changes, of atrial channels in hypertensive patients, and there are some congenital defects in CGRP or heart channels in genetic hypertensive models. Thus, Sprague-Dawley (SD) rats were employed to establish classical hypertensive model, "two-kidney-one-clip (2K1C)" Goldblatt renovascular hypertensive rat. We observed the dynamic changes of iCGRP(immune reaction positive to CGRP) in plasma, spine and auricles, mRNA change of CGRP in spine and auricles, and mRNA changes of a subunit of Na+ channel (Na+- a),alC subunit of L type Ca2+ channel (CaL- aIC), Na+-Ca2+ exchanger (NCX), a subunit of transient outward K+ channel (Kv4.3), to analyze the relationship among the changes of blood pressure,' CGRP and ion channels. We observed the effect of CGRP on ICa,L, Ito, /Na of isolated cells from normal rats' auricles to reveal the evidence that CGRP could play a role in electrical remodeling of atria at cellular level. At the same time, we used a kind of Ca2+ antagonist-diltiazam to treat hypertensive rats to investigate the protectivemechanism of Ca2+ antagonist on Ca2+ homeostasis of atrial cells. MethodsSD rats were provided by Animal Center of Dalian Medical University, age 6-7 weeks, body weight 150-180 g, natural day and night, taking food and water freely. "2K1C" hypertensive rats were established by adding a silver clip 0.22-0.25 mm in diameter to left renal artery, while right kidney remained intact. The left renal artery of sham-operated rat was isolated, but no clip was added. Systolic blood pressure was measured twice a week by tail-cuff method.One milliliter blood was taken from posterior orbital venous pluxes of each rat in both "2K1C" rats and sham rats group 1, 2, 4, 6 week after operation, plasma was separated and kept at -70℃. Radio-immunologic assay was used to measure iCGRP in plasma. Upper segment of spine, left and right auricle of five groups rats (normal rats, sham rats, "2K1C" rats 2, 4, 6 weeks after operation) was taken out and kept at -70℃. Total RNA and protein of separated tissue were extracted to measure mRNA and iCGRP. The iCGRP in spine, left and right auricle of each group was analyzed and compared by method of Westemblot. CGRP mRNA of spine, left and right auricle was compared by method of semiquatitative RT-PCR. mRNA of Na+-a, CaL-aIC, NCX, Kv4.3 in left and right auricle was analyzed by RT-PCR also. The effect of two different concentration CGRP (0.05 u M and 0.12 u M) on INa, ICa,L and Ito of isolated cells from normal rats' auricles was observed by method of whole-cell patch-clamp.In another experiment, "2K1C" rats were divided into three groups, high dosage (HD) group was given 250 mg/kg/d diltiazam, low dosage (LD) group was given 50 mg/kg/d, control group was given vehicle. Treatment began one week after operation, the drug was given intragastrically twice a day. After 4 weeks treatment, "2K1C" and sham rats were killed. iCGRP in spine and auricle was analyzed by Westemblot, mRNA of CaL- aIC, and NCX in auricles was measured by semiquatitative RT-PCR.
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