Single pancreatic beta-cells from normal rats exhibit an initial decrease and subsequent increase in cytosolic free Ca2+ in response to glucose.
Since it was reported that glucose stimulation initially lowers as well as subsequently raises the cytosolic free calcium concentration [( Ca2+]i) in pancreatic islet cells from hyperglycemic ob/ob mice, it has been argued whether the lowering of [Ca2+]i is physiological or artifactual. In the present study, [Ca2+]i in single pancreatic beta-cells from normal rats was measured by Fura-2 microfluorometry. Following elevation of the glucose concentration from 2.8 mM (basal) to 16.7 mM, a bimodal change in [Ca2+]i, an initial decrease and subsequent increase, was demonstrated. When the basal glucose concentration was raised to 5.6 mM, the stimulation with 16.7 mM glucose also induced the decrease in [Ca2+]i in the majority of the cells, though the amplitude of the decrease was reduced. An elevation of the glucose concentration from 2.8 to 5.6 mM induced the decrease in [Ca2+]i but not usually the increase in [Ca2+]i. Removal of extracellular Ca2+ eliminated the increase in [Ca2+]i without affecting the decrease in [Ca2+]i. Thus, the decrease and increase in [Ca2+]i were clearly dissociated under certain conditions. In contrast, mannoheptulose (an inhibitor of glucose metabolism) inhibited both the decrease and increase in [Ca2+]i. These results demonstrate that the glucose-induced bimodal change in [Ca2+]i is a physiological response of islet beta-cells, and that the decrease and increase in [Ca2+]i are generated by mutually-independent mechanisms which are operated through glucose metabolism by islet beta-cells.
Yada
T
T
Department of Physiology, Kagoshima University School of Medicine, Japan.
Kakei
M
M
Tanaka
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D016257:Fura-2; D005947:Glucose / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism; D008356:Mannoheptulose / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D008356:Mannoheptulose; D005947:Glucose; D002118:Calcium; D016257:Fura-2