| Objective To investigate the altering of potassium currents in ventricular myocytes of rats with diabetes mellitus(DM) and to explore the molecular mechanism for the remodeling.Methods 1. Male Sprague-Dawley(SD) rats weighing 150～200 g were made diabetic by a single intraperitoneal injection of STZ at a dose of 65 mg/kg. Normal rats(n=15) of similar age and body weight used as controls were injected with vehicle only(0.1 mol/L citrate buffer, pH 4.5). 3 days after injection blood glucose (BG) was measured, treating rats of BG >16.7mmol/L as successfully established diabetic models (n=14).2. Single ventricular myocytes were isolated through Langendoff enzymatic perfusion. Currents were recorded using whole-cell patch clamp technique for cell capacitance(Cm) and current densities of transient outward potassium current(Ito), steady-state outward potassium current(Iss), inward rectifier potassium current(IK1) separately, and then depicted I-V(current density to each clamp voltage ) curve for each current.3. The total mRNA was extracted through the Trizol-Chloroform-isopropanol method, followed by a reverse transcription kit to produce cDNA. The cDNA was then amplified with special pair primers through polymerase chain reaction(PCR), whose products were semi-quantitative to evaluate the gene expression levels separately for Kv1.4,Kv4.2 and Kv4.3α-subunits encoding transient outward potassium channel, using relative OD value withβ-actin.Results 1. Each diabetic rat was presented with typical clinical symptoms of DM. The body weights of diabetic rats were significantly decreased compared with those of controls, with(165.93±8.99)g(n=14)in DM group and(227.27±7.40)g(n=15) in control group(P<0.01). while BG of diabetic rats stayed at high level with average value about 20mmol/L, in contrast with controls(5.47±0.31)mmol/L(P<0.01).2.①There was no significant difference in membrane capacitance of ventricular myocytes between diabetic rats[(108.24±25.00)pF(n = 29)] and controls[(118.18±27.16)pF(n=9)];②The density of Ito (+70mV) was significantly decreased in diabetic rats[(18.91±3.27)pA/pF(n=29)] compared with controls[(30.59±3.84)pA/pF(n=9)] (P<0.01);③The density of Iss fell by 21%, with(4.45±1.79)pA/pF(n=29) in DM group and(5.64±2.26)pA/pF(n=9) in control group, but with no statistic significance;④No change occurred for IK1,the densities in DM group and control were (16.75±1.51)pA/pF(n=29) and (15.79±1.67)pA/pF(n=9) respectively.3. The gene expression levels of Kv4.2 and Kv4.3 encoding theαsubunit of Ito in DM group were markedly decreased in contrast with those of controls, by 56.88% and 46.57% respectively. But the level of Kv1.4 mRNA increased by 48.02% in DM group (P<0.01).Conclusions 1. Diabetic model can be successfully established by STZ intraperitoneal injection.2. The density of Ito was down regulated in ventricular myocytes of diabetic rats.3. Compared with control rats, the gene expression of Kv4.2 and Kv4.3 encoding Ito channelαsubunits were both decreased in diabetic rats, while increased for Kv1.4 gene expression in DM group. This indicates that down regulation of Ito in diabetic rat ventricular myocytes is attributed to the decreased gene expression of channel-formingαsubunits.
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