title: Glucose increases extracellular [Ca2+] in rat insulinoma (INS-1E) pseudoislets as measured with Ca2+-sensitive microelectrodes.
abstract: Secretory granules of pancreatic β-cells contain high concentrations of Ca2+ ions that are co-released with insulin in the extracellular milieu upon activation of exocytosis. As a consequence, an increase in the extracellular Ca2+ concentration ([Ca2+]ext) in the microenvironment immediately surrounding β-cells should be expected following the exocytotic event. Using Ca2+-selective microelectrodes we show here that both high glucose and non-nutrient insulinotropic agents elicit a reversible increase of [Ca2+]ext within rat insulinoma (INS-1E) β-cells pseudoislets. The glucose-induced increases in [Ca2+]ext are blocked by pretreatment with different Ca2+ channel blockers. Physiological agonists acting as positive or negative modulators of the insulin secretion and drugs known to intersect the secretory machinery at different levels also induce [Ca2+]ext changes as predicted on the basis of their described action on insulin secretion. Finally, the glucose-induced [Ca2+]ext increase is strongly inhibited after disruption of the actin web, indicating that the dynamic [Ca2+]ext changes recorded in INS-1E pseudoislets by Ca2+-selective microelectrodes occur mainly as a consequence of exocytosis of Ca2+-rich granules. In conclusion, our data directly demonstrate that the extracellular spaces surrounding β-cells constitute a restricted domain where Ca2+ is co-released during insulin exocytosis, creating the basis for an autocrine/paracrine cell-to-cell communication system via extracellular Ca2+ sensors.
authors.affiliation: Department of Biosciences, Biotechnology and Pharmacological Sciences, University of Bari, Via G. Amendola 165/A, 70126 Bari, Italy. gerbino@biologia.uniba.it
authors.forename: Andrea
authors.initials: A
authors.lastname: Gerbino
authors.forename: Isabella
authors.initials: I
authors.lastname: Maiellaro
authors.forename: Claudia
authors.initials: C
authors.lastname: Carmone
authors.forename: Rosa
authors.initials: R
authors.lastname: Caroppo
authors.forename: Lucantonio
authors.initials: L
authors.lastname: Debellis
authors.forename: Maria
authors.initials: M
authors.lastname: Barile
authors.forename: Giovanni
authors.initials: G
authors.lastname: Busco
authors.forename: Matilde
authors.initials: M
authors.lastname: Colella
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D002450:Cell Communication / Q000187:drug effects; D060833:Cellular Microenvironment / Q000187:drug effects; D005089:Exocytosis; D005947:Glucose / Q000008:administration & dosage*; D005905:Glyburide / Q000008:administration & dosage; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism; D008839:Microelectrodes; D051381:Rats; D022142:Secretory Vesicles / Q000187:drug effects
chemical_list: D002121:Calcium Channel Blockers; D007328:Insulin; D005947:Glucose; D005905:Glyburide; D002118:Calcium