| Objective: (1) To observe the effect of DMA on rat isolated arterial rings obtained from different organs and to have a clearer insight into its pharmacological mechanism. (2) To study the effect of DMA on membrane ionic currents (Sodium-calcium exchange, calcium current and sodium current) between normal and hypertrophic myocytes of rats.Methods: (1) The rats were sacrificed by luxation and arteries were quickly removed from different organs and placed in physiological salt solution (PSS) at 4℃. The arteries were carefully cleaned of adherent fat and connective tissue then were cut into rings (2mm in length) and mounted on wolfram filament (40μm in diameter) in the chambers of Multi Myograph System-610M (Danish Myo Technology A/S, DMT) for measurement of isometric tension and the signal is collected by Chart 5.3 in the computer; they were bathed in PSS solution (37℃) gassed with 100%O2. (2) Cardiac hypertrophy was induced in Wister rats by oral administrating L-thyroxine for 7 days. The heart to body weight ratio of normal Wistar rats was HW/BW = 3.19±0.18mg/g, VW/BW = 2.61±0.21mg/g; and the heart to body weight ratio of rats by administrating L-thyroxine was HW/BW=4.58±0.44mg/g, VW/BW=3.81±0.61mg/g. (P< 0.01, n=10) , respect. Microscope television videptoping exhibiting: mean myocyte diameter was significantly greater and interslitial collagen was increased in ventricles of L-Thy treated group compared with controls. These differences suggest that rats of administrating L-Thy have heart hypertrophy and hypertrophied myocytes. Single ventricular myocytes from normal rats and myocardial hypertrophic rats were prepared using enzymatic dispersion. ICa-L, INa, and INa/Ca in the cellular membrane were observed using whole cell voltage-clamp recording.Results: (1) DMA (1×10-6,3×10-6,1×10-5,3×10-5mol/L) showed no significant effect on 60 mmol/L KCl-induced contraction of rat middle cerebral artery, coronary artery, renal artery and superior mesenteric artery rings. At the concentration of 3×10-7, 1×10-6, 3×10-6 and 1×10-5 mol/L, DMA exerts significant inhibitive effect on rat renal artery rings which were contracted by phenylephrine (Phe) in a dose-dependent manner. DMA significantly decreased Phe-induced contractions by 20% to 45% and we can see the characteristic of noncompetitive antagonism. At the concentration of 3×10-7, 1×10-6, 3×10-6and 1×10-5mol/L, The significant inhibitive effect of DMA on rat superior mesenteric artery rings that were contracted by phenylephrine in a dose-dependent manner. DMA significantly decreased Phe-induced contractions by 20% to 50% and we can also see the characteristic of noncompetitive antagonism. At the concentration of 1×10-6, 3×10-6,1×10(-5),3×10-5and 6×10-5mol/L, DMA significantly decreased Phe (10μmol/L)-induced contractions by 45.75±1.89%( P<0.05, n=6) on rat renal artery rings and the IC20 was 6.61±1.65μmol/L, while sodium chloride in same concentration as DMA does not show any effect on it. At the concentration of 1×10-6,3×10-6,1×10-5,3×10-5and 6×10-5mol/L, DMAsignificantly decreased Phe(10μmol/L)-induced contractions by 47.04±1.42%( P<0.05, n=6) on rat superior mesenteric artery rings and the IC20 was 5.25±1.36μmol/L, while sodium chloride which had the same concentration with DMA had no effect on it. (2) The effect of DMA on ion channel and sodium-calcium exchange current: DMA (10μmol/L) showed no significant effect on ICa-L and INa in ventricular myocytes from normal and myocardial hypertrophic rats. DMA (10μmol/L) can agitate INa/Ca. DMA increased outward INa/Ca from 106.89±8.54pA to 135.10±13.71pA (P<0.05, n=4) by 26.18±3.76% at the potential of 70 mV. DMA increased inward INa/Ca from -122.70±11.42pA to -176.27±14.92pA (P<0.05, n=4) by 43.76±10.91% at the potential of -70 mV. At the concentration of 20μmol/L, DMA increased outward INa/Ca from 106.89±8.54pA to 183.31±15.02pA (P<0.05,n=4) by 71.47±1.60% at the potential of 70 mV. DMA increased inward INa/Ca from -122.70±11.42pA to -256.90±17.19pA (P<0.05, n=4) by 109.77±5.75% at the potential of-70 mV.Conclusions: (1) DMA (1×10-6,3×10-6,1×10-5,3×10-5mol/L) showed no significant effecton 60 mmol/L KCl-induced contraction of rat middle cerebral artery, coronary artery, renal artery and superior mesenteric artery rings.(2) At the concentration of 3×10-7,1×10-6,3×10-6and1×10-5mol/L, DMA shows significant inhibitive effects on rat renal artery superior mesentericartery rings that are contracted by phenylephrine (Phe) in a dose-dependent manner. (3)DMA(3×10-7,1×10-6,3×10-6 and 1×10-5mol/L) significantly decreased Phe (10μmol/L)-inducedcontractions in a dose-dependent manner on rat renal artery rings and superior mesenteric artery rings. (4) DMA (10μmol/L) was no any effection on ICa-L and INa in ventricular myocytes from normal and myocardial hypertrophic rats. (5) At the concentration of 10μmol/L and 20μmol/L, DMA can increase the INa/Ca in ventricular myocytes from myocardial hypertrophic rats, and the amplitude of inward INa/Ca significantly greater than that of outward INa/Ca. |
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