Inhibition of Sarcoplasmic Reticulum Ca2+ Uptake by Pyruvate and Fatty Acid in H9c2 Cardiomyocytes: Implications for Diabetic Cardiomyopathy

High extracellular glucose concentration was reported to suppress intracellular Ca2+ clearing through altered sarcoplasmic reticulum (SR) function. In the present study, we attempted to elucidate the effects of pyruvate and fatty acid on SR function and reveal the mechanistic link with glucose-induced SR dysfunction. For this purpose, SR Ca2+-uptake rate was measured in digitonin-permeabilized H9c2 cardiomyocytes cultured in various conditions. Exposure of these cells to 5 mM pyruvate for 2 days induced a significant suppression of SR Ca2+-uptake, which was comparable to the effects of high glucose. These effects were accompanied with decreased glucose utilization. However, pyruvate could not further suppress SR Ca2+-uptake in cells cultured in high glucose condition. Enhanced entry of pyruvate into mitochondria by dichloroacetate, an activator of pyruvate dehydrogenase complex, also induced suppression of SR Ca2+-uptake, indicating that mitochondrial uptake of pyruvate is required in the SR dysfunction induced by pyruvate or glucose. On the other hand, augmentation of fatty acid supply by adding 0.2 to 0.8 mM oleic acid resulted in a dose-dependent suppression of SR Ca2+-uptake. However, these effects were attenuated in high glucose-cultured cells, with no significant changes by oleic acid concentrations lower than 0.4 mM. These results demonstrate that (1) increased pyruvate oxidation is the key mechanism in the SR dysfunction observed in high glucose-cultured cardiomyocytes; (2) exogenous fatty acid also suppresses SR Ca2+-uptake, presumably through a mechanism shared by glucose.

Interactions between Estradiol-17beta-BSA and Calcitropic Hormones in Ca2+ Uptake in Renal Proximal Tubule Cells

The aim of the present study was to investigate the interaction of estradiol-17beta-bovine serum albumin (E2-BSA) and calcitropic hormones, such as parathyroid hormone, calcitonin, and vitamin D, in regulation of Ca2+ uptake in primary cultured renal proximal tubule cells. Statistically significant increase in Ca2+ uptake was found from 2 hours after E2-BSA (10(-9) M) treatment, while estradiol-17beta (10(-9) M) did not affect. Treatment of the cells with E2-BSA (10(-9) M) together with parathyroid hormone (PTH) (10(-8) M), vitamin D (10(-8) M), or calcitonin (10(-8) M) significantly stimulated Ca2+ uptake by 32.50%, 29.30%, or 27.75%, respectively, compared with the control. However, calcitropic hormones did not exhibit any synergistic effect on the E2-BSA-induced stimulation. E2-BSA significantly increased cAMP generation and PKC activity. The stimulatory effect of cotreatment of E2-BSA and PTH or vitamin D was blocked by SQ22536 (an adenylate cyclase inhibitor) and staurosporine (a PKC inhibitor), but the effect of cotreatment of E2-BSA and calcitonin was not blocked. Furthermore, 8-Br-cAMP and TPA (an artificial PKC promoter) increased Ca2+ uptake by 25.51% and 16.47%, respectively, compared with the control. In conclusion, E2-BSA combined with calcitropic hormones regulated Ca2+ uptake partially via cAMP and PKC-dependent mechanisms in renal proximal tubule cells.

Preliminary Study on the Mechanism of the Effects of Etimicin and Gentamicin on Cellular Calcium / 中国药房

0.05.They at10mmol/L significantly increased [Ca 2+ ]i,P3.4?10 -1 mmol/L significantly inhibited endoplasmic Ca 2+ -uptake,P

Decrease in Ca2+ storage in the cardiac sarcoplasmic reticulum of diabetic rat

In order to elucidate the molecular mechanism of the intracellular Ca2+ overload frequently reported from diabetic heart, diabetic rats were induced by the administration of streptozotocin, the membrane vesicles of junctional SR (heavy SR, HSR) were isolated from the ventricular myocytes, and SR Ca2+ uptake and SR Ca2+ release were measured. The activity of SR Ca2+-ATPase was 562 +/- 14 nmol/min/mg protein in control heart. The activity was decreased to 413 +/- 30 nmol/min/mg protein in diabetic heart and it was partially recovered to 485 +/- 18 nmol/min/mg protein in insulin-treated diabetic heart. A similar pattern was observed in SR 45Ca2+ uptakes; the specific uptake was the highest in control heart and it was the lowest in diabetic heart. In SR 45Ca2+ release experiment, the highest release, 45% of SR 45Ca2+, was observed in control heart. The release of diabetic heart was 20% and it was 30% in insulin-treated diabetic heart. Our results showed that the activitiesof both SR Ca2+-ATPase and SR Ca2+ release channel were decreased in diabetic heart. In order to evaluate how these two factors contribute to SR Ca2+ storage, the activity of SR Ca2+-ATPase was measured in the uncoupled leaky vesicles. The uncoupling effect which is able to increase the activity of SR Ca2+-ATPase was observed in control heart; however, no significant increments of SR Ca2+-ATPase activities were measured in both diabetic and insulin-treated diabetic rats. These results represent that the Ca2+ storage in SR is significantly depressed and, therefore, Ca2+-sequestering activity of SR may be also depressed in diabetic heart.

Calcium uptake and Ca2+-ATPase activity in goat spermatozoa membrane vesicles do not require Mg2+.

Microsomal membrane vesicles isolated from goat spermatozoa contain Ca2+- ATPase, and exhibit Ca2+ transport activities that do not require exogenous Mg2+ .The enzyme activity is inhibited by calcium-channel inhibitors, e.g. verapamil and diltiazem, like the well known Ca2+ , Mg2+-ATPase. The uptake of calcium is ATP (energy)- dependent and the accumulated Ca2+ can be completely released by the Ca2+ ionophore A23187, suggesting that a significant fraction of the vesicles are oriented inside out.