Different effects of the ionophore A-23187 and D-glucose on 45Ca2+ fluxes in isolated islets of ob/ob-mice.
Fluxes of 45Ca2+ were studied in beta-cell rich islets of non-inbred ob/ob-mice, using LaCl3 to wash out extra-cellular and superficially bound 45Ca2+. The ionophore A-23187 (10 microM) increased the 45Ca2+ uptake in islets both at 3 and 20 mM D-glucose, the effect being more pronounced after 10 min than after 120 min of incubation. In incubations for 120 min, 20 mM D-glucose induced a higher uptake of 45Ca2+ than did A-23187. The ionophore enhanced the unidirectional efflux of 45Ca2+ from preloaded islets. Pretreatment of islets with 20 mM D-glucose in non-radioactive medium inhibited the subsequent D-glucose-induced 45Ca2+ uptake. Similar pretreatment with A-23187 increased the subsequent ionophore-induced 45Ca2+ uptake. The results suggest that A-23187 acts by catalyzing Ca2+ fluxes across the beta-cell plasma membrane. The different effects of D-glucose and A-23187 on 45Ca2+ fluxes suggest that the two agents act through different mechanisms in the beta-cells.
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice
D000900:Anti-Bacterial Agents; D000001:Calcimycin; D005947:Glucose; D002118:Calcium