Further studies on the relationship between insulin release and lanthanum-nondisplaceable 45Ca2+ uptake by pancreatic islets: effects of fructose and starvation.
Relationships between the release of insulin and the incorporation of 45Ca2+ into a lanthanum-nondisplaceable (intracellular) pool were studied in islets microdissected from the pancreatic glands of non-inbred ob/ob mice. In comparison with D-glucose, D-fructose was slowly oxidized and had only marginal effects on insulin release. However, fructose was as effective as glucose in stimulating the lanthanum-nondisplaceable 45Ca2+ uptake. The 45Ca2+ uptake was dose-dependent on the concentration of fructose in the range 0-20 mM; the same dose-dependence was obtained with glucose. Fasting the mice for 3 days caused a total block of the insulin secretory response to 20 mM glucose, but it produced an enhancement of the glucose-induced 45Ca2+ uptake. Both the inhibition of insulin release and the enhancement of 45Ca2+ uptake were counteracted by pretreating the isolated islets with 20-40 mM D-glucose; pretreatment with L-glucose or fructose could not counteract the effects of fasting. Although some functional relationship may exist between the lanthanum-nondisplaceable uptake of 45Ca2+ and the insulin secretory apparatus, it is concluded that the uptake of Ca2+ is not simply the result of stimulated insulin release.
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D005215:Fasting; D005632:Fructose / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D051379:Mice
D007328:Insulin; D005632:Fructose; D005947:Glucose; D002118:Calcium