title: Inhibition of connexin 36 hemichannels by glucose contributes to the stimulation of insulin secretion.
abstract: The existence of functional connexin36 (Cx36) hemichannels in β-cells was investigated in pancreatic islets of rat and wild-type (Cx36(+/+)), monoallelic (Cx36(+/-)), and biallelic (Cx36(-/-)) knockout mice. Hemichannel opening by KCl depolarization was studied by measuring ATP release and changes of intracellular ATP (ADP). Cx36(+/+) islets lost ATP after depolarization with 70 mM KCl at 5 mM glucose; ATP loss was prevented by 8 and 20 mM glucose or 50 μM mefloquine (connexin inhibitor). ATP content was higher in Cx36(-/-) than Cx36(+/+) islets and was not decreased by KCl depolarization; Cx36(+/-) islets showed values between that of control and homozygous islets. Five minimolar extracellular ATP increased ATP content and ATP/ADP ratio and induced a biphasic insulin secretion in depolarized Cx36(+/+) and Cx36(+/-) but not Cx36(-/-) islets. Cx36 hemichannels expressed in oocytes opened upon depolarization of membrane potential, and their activation was inhibited by mefloquine and glucose (IC₅₀ ∼8 mM). It is postulated that glucose-induced inhibition of Cx36 hemichannels in islet β-cells might avoid depolarization-induced ATP loss, allowing an optimum increase of the ATP/ADP ratio by sugar metabolism and a biphasic stimulation of insulin secretion. Gradual suppression of glucose-induced insulin release in Cx36(+/-) and Cx36(-/-) islets confirms that Cx36 gap junction channels are necessary for a full secretory stimulation and might account for the glucose intolerance observed in mice with defective Cx36 expression. Mefloquine targeting of Cx36 on both gap junctions and hemichannels also suppresses glucose-stimulated secretion. By contrast, glucose stimulation of insulin secretion requires Cx36 hemichannels' closure but keeping gap junction channels opened.
authors.affiliation: Biochemistry Department, Medical School, Complutense University, Madrid, Spain;
authors.forename: Javier
authors.initials: J
authors.lastname: Pizarro-Delgado
authors.affiliation: Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain;
authors.forename: Ilaria
authors.initials: I
authors.lastname: Fasciani
authors.affiliation: Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain;
authors.forename: Ana
authors.initials: A
authors.lastname: Temperan
authors.affiliation: Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain;
authors.forename: María
authors.initials: M
authors.lastname: Romero
authors.affiliation: Center for Biomedical Technology, Universidad Politécnica, Madrid, Spain;
authors.forename: Daniel
authors.initials: D
authors.lastname: González-Nieto
authors.affiliation: Institute of Bioengineering and CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Miguel Hernández University, Elche, Spain;
authors.forename: Paloma
authors.initials: P
authors.lastname: Alonso-Magdalena
authors.affiliation: Department of Pathology and Experimental Therapeutics, Faculty of Medicine - Campus Bellvitge, University of Barcelona, Hospitalet del Llobregat, Barcelona, Spain; IDIBELL, Institut d'Investigació Biomèdica de Bellvitge, Hospitalet del Llobregat, Barcelona, Spain;
authors.forename: Anna
authors.initials: A
authors.lastname: Nualart-Marti
authors.affiliation: CIBERDEM, Barcelona, Spain; Department of Clinical Sciences, University of Barcelona, Feixa Llarga s/n, L'Hospitalet de Llobregat, Barcelona, Spain; and.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Estil'les
authors.affiliation: Department of Neurobiology, Harvard Medical School, Boston, Massachusetts;
authors.forename: David L
authors.initials: DL
authors.lastname: Paul
authors.affiliation: Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain;
authors.forename: Rafael
authors.initials: R
authors.lastname: Martín-del-Río
authors.affiliation: CIBERDEM, Barcelona, Spain; Department of Clinical Sciences, University of Barcelona, Feixa Llarga s/n, L'Hospitalet de Llobregat, Barcelona, Spain; and Endocrine Unit, Hospital Universitari Bellvitge-IDIBELL, Barcelona, Spain.
authors.forename: Eduard
authors.initials: E
authors.lastname: Montanya
authors.affiliation: Department of Pathology and Experimental Therapeutics, Faculty of Medicine - Campus Bellvitge, University of Barcelona, Hospitalet del Llobregat, Barcelona, Spain; IDIBELL, Institut d'Investigació Biomèdica de Bellvitge, Hospitalet del Llobregat, Barcelona, Spain;
authors.forename: Carles
authors.initials: C
authors.lastname: Solsona
authors.affiliation: Institute of Bioengineering and CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Miguel Hernández University, Elche, Spain;
authors.forename: Angel
authors.initials: A
authors.lastname: Nadal
authors.affiliation: Research Department, "Ramón y Cajal" Hospital-IRYCIS, Madrid, Spain;
authors.forename: Luis Carlos
authors.initials: LC
authors.lastname: Barrio
authors.affiliation: Biochemistry Department, Medical School, Complutense University, Madrid, Spain; tamarit@med.ucm.es.
authors.forename: J
authors.initials: J
authors.lastname: Tamarit-Rodríguez
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001786:Blood Glucose / Q000032:analysis / Q000378:metabolism*; D017630:Connexins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism; D018149:Glucose Intolerance / Q000097:blood / Q000378:metabolism*; D006579:Heterozygote; D006943:Hyperglycemia / Q000209:etiology / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D049990:Membrane Transport Modulators / Q000494:pharmacology; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D046509:Tissue Culture Techniques; D015854:Up-Regulation / Q000187:drug effects; D000097004:Gap Junction delta-2 Protein
chemical_list: D000255:Adenosine Triphosphate; D001786:Blood Glucose; D017630:Connexins; D007328:Insulin; D049990:Membrane Transport Modulators; D011994:Recombinant Proteins; D000097004:Gap Junction delta-2 Protein
keywords: connexin 36; gap junction channels; glucose; hemichannels; insulin secretion; islets