Evidence for Mechanistic Alterations of Homeostasis in Type 2 Diabetes Mellitus
Altered cytosolic is implicated in the aetiology of many diseases including diabetes but there are few studies on the mechanism(s) of the altered regulation. Using human lymphocytes, we studied cytosolic calcium () and various transport mechanisms in subjects with Type 2 diabetes mellitus and control subjects. -specific fluorescent probes (Fura-2 and Fluo-3) were used to monitor the signals. Thapsigargin, a potent and specific inhibitor of the sarco(endo)plasmic reticulum -ATPase (SERCA), was used to study - store dependent fluxes. Significant (P < 0.05) elevation of basal levels was observed in lymphocytes from diabetic subjects. levels were positively correlated with fasting, plasma glucose and HbAlc. There was also a significant (P < 0.05) reduction in plasma membrane calcium (PMCA) ATPase activity in diabetic subjects compared to controls. Cells from Type 2 diabetics exhibited an increased influx (as measured both by Fluo-3 fliorescence and assays) as a consequence of of thapsigargin-mediated store depletion. Upon addition of (a surrogate of ), the fura-2 fluorescence decayed in an exponential fashion and the rate and extent of this decline was steeper and greater in cells from type 2 diabetic patients. There was also a significant (P < 0.05) difference in the exchange activity in Type 2 diabetic patients, both under resting conditions and after challenging the cells with thapsigargin, when the internal store sequestration was circumvented. Pharmacological activation of protein kinase C (PKC) in cells from patients resulted in only partial inhibition of entry. We conclude that cellular accumulation in cells from Type 2 diabetes results from (a) reduction in PMCA ATPase activity, (b) modulation of exchange and (3) increased influx across the plasma membrane.
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