title: Glucose-stimulated insulin secretion of insulinoma INS-1E cells is associated with elevation of both respiration and mitochondrial membrane potential.
abstract: Increased ATP/ADP ratio resulting from enhanced glycolysis and oxidative phosphorylation represents a plausible mechanism controlling the glucose-stimulated insulin secretion (GSIS) in pancreatic beta-cells. Although specific bioenergetics might be involved, parallel studies of cell respiration and mitochondrial membrane potential (DeltaPsi(m)) during GSIS are lacking. Using high resolution respirometry and parallel DeltaPsi(m) monitoring by two distinct fluorescence probes we have quantified bioenergetics in rat insulinoma INS-1E cells representing a suitable model to study in vitro insulin secretion. Upon glucose addition to glucose-depleted cells we demonstrated a simultaneous increase in respiration and DeltaPsi(m) during GSIS and showed that the endogenous state 3/state 4 respiratory ratio hyperbolically increased with glucose, approaching the maximum oxidative phosphorylation rate at maximum GSIS. Attempting to assess the basis of the "toxic" effect of fatty acids on insulin secretion, GSIS was studied after linoleic acid addition, which diminished respiration increase, DeltaPsi(m) jump, and magnitude of insulin release, and reduced state 3/state 4 dependencies on glucose. Its effects were due to protonophoric function, i.e. uncoupling, since without glucose, linoleic acid accelerated both state 3 and state 4 respiration by similar extent. In turn, state 3 respiration increased marginally with linoleic acid at 10-20mM glucose. We conclude that upon glucose addition in physiological range, the INS-1E cells are able to regulate the oxidative phosphorylation rate from nearly zero to maximum and that the impairment of GSIS by linoleic acid is caused by mitochondrial uncoupling. These findings may be relevant to the pathogenesis of type 2 diabetes.
authors.affiliation: Department of Membrane Transport Biophysics, No. 75, Institute of Physiology, Academy of Sciences of the Czech Republic, Vídenská 1083, 14220 Prague 4, Czech Republic. spacek@biomed.cas.cz
authors.forename: Tomás
authors.initials: T
authors.lastname: Spacek
authors.forename: Jitka
authors.initials: J
authors.lastname: Santorová
authors.forename: Klára
authors.initials: K
authors.lastname: Zacharovová
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Berková
authors.forename: Lydie
authors.initials: L
authors.lastname: Hlavatá
authors.forename: Frantisek
authors.initials: F
authors.lastname: Saudek
authors.forename: Petr
authors.initials: P
authors.lastname: Jezek
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D005947:Glucose / Q000494:pharmacology*; D007340:Insulinoma / Q000378:metabolism*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D019787:Linoleic Acid / Q000494:pharmacology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects*; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D014407:Tumor Cells, Cultured
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D019787:Linoleic Acid; D005947:Glucose