Stimulus-secretion coupling of glucose-induced insulin release. X. Effect of glucose on  45 Ca efflux from perifused islets

Uptake of 45Ca2+ by a microsomal fraction from isolated pancreatic islets of non-inbred ob/ob mice was studied. ATP strongly stimulated 45Ca2+ uptake, the maximum effect being obtained with 2mM-ATP. GTP and CTP at this concentration did not increase the uptake. Scatchard analysis revealed at least two types of uptake mechanisms in the presence of 2 mM-ATP; the apparent association constants were 1.1 x 105rvm1 and less than 2.5 x 102M-1. In contradistinction to an unaffected low-affinity uptake, the highaffinity uptake was drastically decreased on omission of ATP. The ATP-dependent and high-affinity uptake was half-saturated at about 10-20M-Ca2+ and was inhibited by 10 or 100puM of cyclic AMP, 10pum cyclic GMP, 10puM cyclic CMP, or 5mM-theophylline.

Section: Discussionmentioning

confidence: 99%

Calcium uptake by subcellular fractions of pancreatic islets. Effects of nucleotides and theophylline

Sehilin

1976

“…Batches of 100-150 islets were incubated for 1 h at 37°C in 1 ml of medium containing lOOpCi of 45Ca and 3mg of glucose/ml in accordance with the studies of Malaisse et al (1973). After incubation islets were washed six times with 3ml of medium which did not contain 45Ca and then peNrifused in the normal way.…”

Section: Methods Andproceduresmentioning

confidence: 99%

Insulin and glucagon secretion from isolated islets of Langerhans. The effects of calcium ionophores

Ashby¹,

Speake²

1975

The role of Ca2+ in the secretion of insulin and glucagon was investigated by studying the effects of Ca2+ ionophores on hormone secretion from isolated perifused islets of Langerhans. lonophore X537A (100pUM), which binds alkaline earth cations and also complexes some univalent cations, caused a rapid transient increase in insulin and glucagon secretion which was not dependent on the presence of Ca2+ in the perifusion medium. Ionophore A23187 (1O4uM), which specifically binds bivalent cations at neutral pH values, similarly increased insulin secretion in complete and Ca2+-free medium, but only stimulated glucagon release in the presence ofextracellular Ca2+. Since the stimulatory effects ofboth ionophores were associated with an increased Ca2+ flux in the islets, these experiments support the hypothesis that Ca2+ may trigger therelease ofinsulin and suggest that it is also involved in the secretion of glucagon. The basal rate of both insulin and glucagon release was significantly increased when Ca2+ was omitted from the perifusion medium, but it is proposed that this finding may be due to adverse effects on cell-membrane function under these conditions.

“…The physiological importance of enhanced Ca2+ (Hellman et al, 1976b); (2) stimnulation of 45Ca2+ release from prelabelled islets (Malaisse et al, 1973;Gylfe & Hellman, 1978;Wollheim et al, 1978); (3) induction of an electric Ca2+ current (Dean & Matthews, 1970;Meissner & Schmelz, 1974).…”

Section: Chemicalsmentioning

confidence: 99%

Polarization of chlorotetracycline fluorescence in pancreatic islet cells and its response to calcium ions and D-glucose

Täljedal¹

1979

Suspensions rich in pancreatic fl-cells were prepared from non-inbred ob/ob-mice, incubated with lO4uM-chlorotetracycline, and analysed for fluorescence polarization in a microscope. Throughout the temperature range 16-380C, fluorescence was enhanced by 5mM-Ca2+ in the incubation medium; 20mM-D-glucose decreased the fluorescence measured in the presence of Ca2+. Fluorescence showed a curvilinear negative regression on temperature. The curves were rectified to a virtually ideal degree by Arrhenius transformations of data. Non-parametric testing of differences between linearized regression lines forms the basis for the following conclusions. The temperature-dependence of fluorescence intensity appeared to be smaller for Ca2+-specific signals than for the background fluorescence of chlorotetracycline in Ca2+-deficient cells. D-Glucose significantly diminished the polarization of fluorescence in cells incubated with Ca2+.