目的：研究小檗碱（Ber）对豚鼠心室细胞钾通道和动作电位作用，以及在蛙卵中表达的人的HERG通道的作用。方法：酶解方法分离单个心肌细胞，采用全细胞膜片箝方法记录钾离子电流及动作电位，基因箝技术研究HERG通道电流。结果：Ber可显著延长动作电位时程，并呈剂量依赖性。Ber 100μmo1/L使APD90由对照的 （450±48）ms 延长至（888±90）ms (n=6，P<0.01)。Ber对Ik1及Ik呈剂量依赖性抑制作用。Ber 100μmo1/L对Ik1的抑制率达65%±7%（n=6,P<0.01）。Ber 50 μmo1/L对Ik的抑制率达57%±6%；对Iktail的抑制率达53%±6%，Ber对Ik作用呈现电压依赖性。Ber对在硅卵中表达的HERG通道具有很强的阻断作用，IC50为75μmo1/L，此阻断作用也呈电压依赖性。结论：Ber可使动作电位时程明显延长，对Ik1及Ik具有阻断作用。Ber可显著抑制HERG通道。Ber抗心律失常的机制与其抑制Ik1、Ik及HERG通道密切相关。

Activation of a calcium-sensing receptor (Ca-SR) leads to increased intracellular calcium concentration and altered cellular activities. The expression of Ca-SR has been identified in both nonexcitable and excitable cells, including neurons and smooth muscle cells. Whether Ca-SR was expressed and functioning in cardiac myocytes remained unclear. In the present study, the transcripts of Ca-SR were identified in rat heart tissues usingRT-PCR that was further confirmed by sequence analysis. Ca-SR proteins were detected in rat ventricular and atrial tissues as well as in isolated cardiac myocytes. Anti-(Ca-SR) Ig did not detect any specific bands after preadsorption with standard Ca-SR antigens. An immunohistochemistry study revealed the presence of Ca-SR in rat cardiac as well as other tissues. An increase in extracellular calcium or gadolinium induced a concentration-dependent sustained increase in [Ca2+]i in isolated ventricular myocytes from adult rats. Spermine (1–10 mM) also increased [Ca2+]i. Pre-treatment of cardiac myocytes with thapsigargin or U73122 abolished the extracellular calcium, gadolinium or spermine-induced increase in [Ca2+]i. The blockade of Na+/Ca2+ exchanger or voltagedependent calcium channels did not alter the extracellular calcium-induced increase in [Ca2+]i. Finally, extracellular calcium, gadolinium and spermine all increased intracellular inositol 1,4,5-triphosphate (IP3) levels. Our results demonstrated that Ca-SR was expressed in cardiac tissue and cardiomyocytes and its function was regulated by extracellular calcium and spermine.

Dopamine receptors exist in many tissues, including rat cardiac tissue. However, the physiological importance ofdopamine receptors in the homeostatic regulation of cardiac function is unclear. In this study, a model of ischaemia/reperfusion was established by culturing primary neonatal rat cardiomyocytes in ischaemia-mimetic solution for 2 hr, followedby incubation in normal culture medium for 24 hr. Lactate dehydrogenase activity, superoxide dismutase activity andmalondialdehyde content were determined colorimetrically with a spectrophotometer. Apoptotic cell death was assayed by3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, terminal deoxynucleotidyl transferase-mediateddUTP-biotin nick end labelling staining and flow cytometry, and morphological alterations were observed with transmissionelectron microscopy. The intracellular free calcium concentration ([Ca2+]i) was measured by confocal laser scanningmicroscopy. Finally, the expression of dopamine receptor 1 (DR1), caspase-3, -8 and -9, Fas, Fas ligand and Bcl-2 and therelease of cytochromecwere analysed by Western blot. The results showed that DR1 expression was increased markedlyduring ischaemia/reperfusion. Treatment with 10M SKF-38393 (DR1 agonist) significantly increased lactate dehydrogenaseactivity, decreased superoxide dismutase activity and increased malondialdehyde content in the culture medium. The DR1agonist promoted the release of cytochromec, accumulation of [Ca2+]i, and apoptosis induced by ischaemia/reperfusion.Furthermore, SKF-38393 up-regulated the expression of caspase-3, -8 and -9, Fas and Fas ligand, and down-regulatedBcl-2 expression. In contrast, 10M SCH-23390 (DR1 antagonist) had no significant effects on the above indicators. Inconclusion, DR1 activation is involved in the apoptosis of cultured neonatal rat cardiomyocytes in simulated ischaemia/reperfusion through the mitochondrial and death receptor pathways.

Polyamines (putrescine, spermidine and spermine) are essential for cell growth and differentiation. Nitric oxideexhibits antihypertrophic functions and inhibits cardiac remodelling. However, the metabolism of polyamines and thepotential interactions with nitric oxide in cardiac hypertrophy remain unclear. We randomly divided Wistar rats into fourtreatment groups: controls, isoproterenol (ISO), ISO and -arginine, and -arginine. Isoproterenol (5mg/kg/day, subcutaneously)and/or?-arginine (800 mg/kg/day, intraperitoneally) was administered once daily for 7 days. The expression ofatrial natriuretic peptide mRNA was determined by reverse transcription-polymerase chain reaction, and fibrogenesis ofheart was assessed by Van Gieson staining. Polyamines were measured with high-performance liquid chromatography, andplasma nitric oxide content and lactate dehydrogenase (LDH) activity were determined with a spectrophotometer. Theexpression levels of ornithine decarboxylase, spermidine/spermine N1-acetyltransferase (SSAT), endothelial nitric oxidesynthase (eNOS) and inducible nitric oxide synthase (iNOS) were analysed by Western blot. Heart-to-body weight ratio,left ventricle-to-body weight ratio, atrial natriuretic peptide mRNA expression, collagen fibres and LDH activity wereelevated, both ornithine decarboxylase and SSAT proteins were up-regulated, and total polyamines were increased in thegroup treated with ISO. Additionally, the expression of iNOS was up-regulated, eNOS was down-regulated, and nitricoxide levels were low. Notably, cotreatment with -arginine reversed most of these changes except for SSAT expression,which was further up-regulated. We propose that increased polyamines and decreased nitric oxide are involved in cardiachypertrophy induced by ISO and suggest that -arginine pre-treatment can attenuate cardiac hypertrophy through theregulation of key enzymes of the polyamine and nitric oxide pathways.