Effects of plasma membrane Ca2+ -ATPase overexpression upon D-glucose metabolism in BRIN-BD11 cells
Résumé
In order to investigate the possible link between plasma membrane Ca2+-ATPase (PMCA) activity and D-glucose catabolism in insulin-producing cells, BRIN-BD11 cells were transfected with two isoforms of PMCA2. Transfection of insulin-producing BRIN-BD11 cells with plasma membrane Ca2+ -ATPase (PMCA2yb and PMCA2wb) was documented by RT-PCR, Western blot analysis, indirect immunofluorescence microscopy and 45Ca2+ uptake by microsomes. In the transfected cells, the overexpression of PMCA coincided with three major anomalies of D-glucose metabolism, namely a lower rate of D-[5-3H]glucose utilization prevailing at a low extracellular concentration of D-glucose (1.1 mM), a low ratio between D-[U-14C]oxidation and D-[5-3H]glucose utilization prevailing at high extracellular glucose concentration (16.7 mM), and a high ratio between the net generation of 14C-labelled acidic metabolites and amino acids and that of 3HOH from D-[5-3H]glucose. These anomalies resulted in a decreased estimated rate of ATP generation (as linked to the catabolism of the hexose) and a lowered ATP cell content, whether at low or high extracellular D-glucose concentration. The net uptake of 45Ca2+ by intact cells was also decreased in the transfected cells, but to a greater extent than apparently attributable to the change in ATP generation rate. These findings document the relevance of plasma membrane Ca2+-ATPase activity to both D- glucose metabolism and Ca2+ handling in insulin-producing cells, with emphasis on the key role for both cytosolic and mitochondrial Ca2+ concentration in the regulation of D-glucose catabolism. They also reveal that over expression of PMCA leads, in insulin-producing cells, to an imbalance between ATP generation and consumption.
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