Abnormalities in cardiac function have been extensively documented in experimental and clinical diabetes. These aberrations are well known to be exaggerated when hypertension and diabetes co-exist. The objective of the present study was to examine whether alterations in the activity of the myocardial Na + -Ca 2+ exchanger (NCX) can account for the deleterious effects of diabetes and (or) hypertension on the heart. To this aim, the following experimental groups were studied: (i) control; (ii) diabetic; (iii) hypertensive; and (iv) hypertensive-diabetic. Wistar rats served as the control group (C) while Wistar rats injected with streptozotocin (STZ, 55 mg/kg) served as the diabetic (D) group. Spontaneously hypertensive (SH) rats were used as the hypertensive group (H) while SH rats injected with STZ served as the hypertensive-diabetic (HD) group. Sarcolemma was isolated from the ventricles of the C, D, H, and HD groups and NCX activity was examined using rapid quenching techniques to study initial rates over a [Ca 2+ ] o range of 10-160 µM. The V max of NCX was lower in the D group when compared with the C group (D, 2.96 ± 0.26 vs. C, 4.0 ± 0.46 nmol·mgprot -1 ·s -1 , P < 0.05), however combined diabetes and hypertension (HD) did not affect the V max of NCX activity (HD, 3.84 ± 0.88 vs. H, 3.59 ± 0.24 nmol·mgprot -1 ·s -1 , P > 0.05). However, analysis of the K m values for Ca 2+ indicated that both the D and HD groups exhibited a significantly lower K m when compared with their respective control groups (D, 42 ± 4 vs. C, 56 ± 4 µM, P < 0.05; HD, 33 ± 7 vs. H, 51 ± 8 µM, P < 0.05). Immunoblotting using polyclonal antibodies (against canine cardiac NCX) exhibited the typical banding of 160, 120, and 70 kDa. The 120 kDa band is believed to represent the native exchanger with its post-translational modifications. Examination of the blots revealed a lower intensity of the 120 kDa band in the D group when compared with the C group, however, no significant difference in the HD group was observed. We speculate that the lower V max in the D group may be due to a reduced concentration of exchanger protein in the membrane. The absence of this defect in the HD group may be a result of compensatory mechanisms to the overall hemodynamic overload, however, this remains to be determined. The increased affinity for Ca 2+ in both the D and HD groups (determined by the lower K m values) is an interesting finding and may be due to changes in sarcolemmal lipid bilayer composition secondary to diabetes-induced hyperlipidemia.Résumé : Les anomalies de la fonction cardiaque au cours du diabète clinique et expérimental ont été largement documentées. On sait que ces aberrations sont amplifiées lorsque diabète et hypertension coexistent. La présente étude a eu pour but d'examiner si les altérations de l'activité de l'échangeur Na + -Ca 2+ (NCX) myocardique peuvent expliquer les effets nocifs du diabète et/ou de l'hypertension sur le coeur. Les groupes expérimentaux suivants ont été examinés : (i) témoin, (ii) diabétique, (iii) hypertendu, e...

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Abnormalities in cardiac function have been extensively documented in experimental and clinical diabetes. These aberrations are well known to be exaggerated when hypertension and diabetes co-exist. The objective of the present study was to examine whether alterations in the activity of the myocardial Na+-Ca2+ exchanger (NCX) can account for the deleterious effects of diabetes and (or) hypertension on the heart. To this aim, the following experimental groups were studied: (i) control; (ii) diabetic; (iii) hypertensive; and (iv) hypertensive-diabetic. Wistar rats served as the control group (C) while Wistar rats injected with streptozotocin (STZ, 55 mg/kg) served as the diabetic (D) group. Spontaneously hypertensive (SH) rats were used as the hypertensive group (H) while SH rats injected with STZ served as the hypertensive-diabetic (HD) group. Sarcolemma was isolated from the ventricles of the C, D, H, and HD groups and NCX activity was examined using rapid quenching techniques to study initial rates over a [Ca2+]o range of 10-160 microM. The Vmax of NCX was lower in the D group when compared with the C group (D, 2.96 +/- 0.26 vs. C, 4.0 +/- 0.46 nmol x mgprot(-1) x s(-1), P < 0.05), however combined diabetes and hypertension (HD) did not affect the Vmax of NCX activity (HD, 3.84 +/- 0.88 vs. H, 3.59 +/- 0.24 nmol x mgprot(-1) x s(-1), P > 0.05). However, analysis of the Km values for Ca2+ indicated that both the D and HD groups exhibited a significantly lower Km when compared with their respective control groups (D, 42 +/- 4 vs. C, 56 +/- 4 microM, P < 0.05; HD, 33 +/- 7 vs. H, 51 +/- 8 microM, P < 0.05). Immunoblotting using polyclonal antibodies (against canine cardiac NCX) exhibited the typical banding of 160, 120, and 70 kDa. The 120 kDa band is believed to represent the native exchanger with its post-translational modifications. Examination of the blots revealed a lower intensity of the 120 kDa band in the D group when compared with the C group, however, no significant difference in the HD group was observed. We speculate that the lower Vmax in the D group may be due to a reduced concentration of exchanger protein in the membrane. The absence of this defect in the HD group may be a result of compensatory mechanisms to the overall hemodynamic overload, however, this remains to be determined. The increased affinity for Ca2+ in both the D and HD groups (determined by the lower Km values) is an interesting finding and may be due to changes in sarcolemmal lipid bilayer composition secondary to diabetes-induced hyperlipidemia.

A porous SiC ceramic reinforced copper-matrix composite was fabricated by spontaneous infiltration of molten Cu-24at%Si alloy into the reinforcement. The influence of process parameters on the infiltration behavior and microstructure of the as-prepared SiC/Cu composite investigations showed that infiltration temperature had an important influence on the infiltration behavior, and higher infiltration temperature which decreased the viscosity of molten Cu-24Si was beneficial to the penetration. Besides, the degree of infiltration increased with the increase of dwelling time at 1600°C. SiC particles were bonded together by sintering additives to form the porous reinforcement, which can be maintained after spontaneous infiltration. The interfacial bond between SiC and Cu-24Si alloy was tight, and no obvious interfacial reaction layer was observed in the as-prepared composite.

Silicon carbide (SiC) reticulated porous ceramics were prepared by organic foam impregnation, using polyurethane sponges as template and deionized water or alcohol as slurry solvent. The sintering behavior, microstructures and apparent density of struct of the SiC reticulated porous ceramics fabricated using the aqueous slurry under different sintering aids and sintering process and the alcohol slurry were investigated comparatively. The experimental results showed that both the microstructures and apparent density of the samples fabricated by Y2O3+AlN as sintering aid were better than those Al2O3 as sintering aid while the aqueous slurry, and the samples fabricated by two-step process (firstly heated to 700 oC in air furnace, and then sintered at 1800 oC in Ar atmosphere) while Y2O3+AlN as sintering aid obtained the optimal properties. In particular, the samples fabricated by the alcohol slurry and reaction sintering process were provided better properties than the aqueous slurry.