Characterization of the process of sodium-calcium exchange in pancreatic islet cells

Abstract

Na(+)-Ca2+ exchange may play a role in Ca2+ extrusion from the pancreatic B-cell. The characteristics of the process working in its reverse mode were examined in normal rat pancreatic islet cells. Isosmotical replacement of extracellular Na+ by sucrose induced a concentration-dependent increase in 45Ca uptake, displaying a pharmacological sensitivity compatible with an uptake mediated by Na(+)-Ca2+ exchange. Glucose, up to 2.8 mM, stimulated reverse Na(+)-Ca2+ exchange. Likewise, membrane depolarization activated the process but only under raised intracellular Na+ activity. In conclusion, the B-cell Na(+)-Ca2+ exchange displays properties similar to those observed in other cells: reversibility and sensitivity to membrane potential. When working in its reverse mode the exchanger displays a quite large capacity. The role played by the exchanger in the process of insulin release warrants further investigation.

Overexpression of the Na/Ca Exchanger Shapes Stimulus-Induced Cytosolic Ca2+ Oscillations in Insulin-Producing BRIN-BD11 Cells

“…3 and 4). In previous studies, we showed that this maneuver stimulated Ca 2ϩ entry and [Ca 2ϩ ] i rise in pancreatic ␤-cells selectively by Na/Ca exchange (reverse mode) (10,11). Figure 3 illustrates the time courses of Na ϩ i -dependent Ca 2ϩ uptake in control and NCX1.7-transfected cells.…”

“…For the measurement of the effect of glucose, the media contained glucose (1.1 or 11.1 mmol/l) without nifedipine. The method used for the measurement of 45 Ca uptake has been described previously (10). Cytosolic Ca 2؉ concentration measurements.…”

“…The exchanger may also reverse during the heart cycle and hence allow Ca 2ϩ entry during the systole (9). In the rat pancreatic ␤-cell, Na/Ca exchange displays a quite high capacity (10) and participates in the control of [Ca 2ϩ ] i and insulin release (11)(12)(13).…”

Plasma Membrane Ca2+-ATPase Overexpression Reduces Ca2+ Oscillations and Increases Insulin Release Induced by Glucose in Insulin-Secreting BRIN-BD11 Cells

“…In brief, BRIN-BD11 cells were preincubated in 1 ml of a nonradioactive solution for 30 min and then incubated for 90 min in 1 ml of the same medium, which also contained 10 Ci/ml 45 Ca 2ϩ . At the end of the incubation, the cells were separated from the incubation medium using a combined lanthanum and oil technique (27). Intracellular Ca 2؉ concentration measurements.…”

Heterozygous inactivation of plasma membrane Ca2+-ATPase in mice increases glucose-induced insulin release and beta cell proliferation, mass and viability

“…The methods used to measure 45 Ca uptake in intact islets and insulin release from perifused islets are described elsewhere [17][18][19][20]. Insulin was assayed using an ELISA kit (Mercodia, Uppsala, Sweden).…”