[Influences and mechanism of verapamil on ischemia/reperfusion injury in cardiomyocytes of streptozotocin-induced diabetes mellitus rats].

OBJECTIVE: To investigate the effects and mechanism of verapamil preventing ischemia/reperfusion (I/R) injury by cardiac performance intracellular free [Ca(2+)](i) and L-type calcium current (I(Ca-L)) in cardiomyocytes of diabetes mellitus rats. METHODS: Diabetic rats were streptozotocin-induced and received verapamil (8 mg×kg(-1)×d(-1)) from 6 - 14 weeks old. The in vitro heart models of I/R rats were randomly divided into normal control group diabetes group, verapamil control group. the changes of heart functions were observed through a Langendorff-perfusion system. The fluorescence intensity of intracellular Ca(2+) was detected with Fluo-3/AM loading by laser scanning confocal microscope. I(Ca-L) was recorded by the whole-cell technique of patch clamp in enzymatically dissociated single rat ventricular myocytes. RESULTS: (1) In verapamil diabetes group, the values of left ventricular developed pressure [(91.3 ± 4.6) mm Hg], diastolic end pressure [(1535 ± 280) mm Hg], the maximum rising rates of left ventricular pressure [(5833 ± 256) mm Hg/s] and coronary arterial flow [(13.7 ± 0.9) ml/min] were all significantly increased, and the maximum dropping rates of left ventricular pressure [(3504 ± 319) mm Hg/s] was obviously decreased (compared with diabetes group, P < 0.01, respectively). (2) The fluorescence intensities of intracellular free Ca(2+)[(155.6 ± 10.9) nmol/L] in verapamil diabetes group were significantly reduced compared with diabetes group (245.2 ± 17.5 nmol/L, P < 0.01). (3) When clamp voltage was -20mV, I(Ca-L) was (-6.81 ± 0.76) pA/pF in verapamil diabetes group (compared with normal group (-8.17 ± 2.07) pA/pF, P < 0.05, and with diabetes group (-3.21 ± 0.54) pA/pF, P < 0.01, and with verapamil control group (-7.14 ± 2.17) pA/pF, P > 0.05). The current-voltage curve was changed to the lower position with -20mV of peak clamp potential in verapamil diabetes group compared with diabetes group. CONCLUSION: A poor heart function is closely correlated with a rising [Ca(2+)]i and a declining I(Ca-L) associated with I/R injury in diabetic rats hearts. Along-term verapamil therapy may significantly improve the severe cardiac impairment. The mechanism is probably attributed to the fact that verapamil can adjust I(Ca-L) influx, normalize the balance of intercellular [Ca(2+)]i, and block the Ca(2+) overload trigger by the effects of Ca(2+)-induced Ca(2+) release in diabetic cardiomyocytes.

[Change of glucose transporter 4 and its influence on glucose and fatty-acid metabolism in type 2 diabetic myocardium].

OBJECTIVE: To investigate the relationship between sarcolemmal content of glucose transporter 4 (GLUT4) and the myocardial glucose and fatty acid utilization in type 2 diabetes. METHODS: Twenty-four Sprague-Dawley rats were randomized into four groups: control, HFD/STZ, control/RSG and HFD/STZ/RSG. Sprague-Dawley rats were fed with high-fat diet (40% of the calories was supplied by fat) for 4 weeks, intraperitoneally injected with 35 mg/kg streptozotocin to establish type 2 diabetes model, and 24 diabetic rats were randomized into four groups: HFD/STZ/RSG group [fed with high fat food and given rosiglitazone (3 mg.kg(-1).d(-1)) for 2 weeks], HFD/STZ group (fed with high fat food and given normal saline), control/RSG [fed with normal food and given rosiglitazone (3 mg.kg(-1).d(-1)) for 2 weeks], and control group (fed with normal food and given normal saline). Then the rats were killed and their hearts were taken out to be mounted onto a Langendorff perfusion apparatus to be perfused with Krebs-Henseleit buffer in the presence of 5 mmol/L glucose and 0.4 mmol/L (3)H labeling palmitate. Glucose uptake and (3)H2O collection were used to evaluate the rate of carbohydrate and fatty acid oxidation. The sarcolemmal content of GLUT4 protein was detected by Western blotting method. RESULTS: Compared with the control group, the diabetic rats had a significantly depression of glucose uptake of the heart [(55 +/- 6) micromol/g dry weight vs (69 +/- 6) micromol/g dry weight, P < 0.01], the oxidation rate of glucose decreased from 25% to 18% and the oxidation rate of palmitate increased from 75% to 82%, and the sarcolemmal GLUT4 content was decreased by 53% after 30 minutes' perfusion. In the HFD/STZ/RSG group the glucose uptake level was (64 +/- 6) micromol/g dry weight, significantly higher than that of the HFD/STZ group (P < 0.05), the proportions of glucose oxidation and fatty acid oxidation were 24% and 76% respectively, and the GLUT4 expression was 92% that of the normal rats, significantly higher than that of the HFD/STZ group (47%, P < 0.01). CONCLUSION: The sarcolemmal GLUT4 content in the type 2 diabetic myocardium is obviously decreased, which may be associated with the decrease of glucose uptake and increase of fatty acid oxygen. Rosiglitazone treatment may exert beneficial effects on the energy substrate utilization by increasing the expression of GLUT4.