title: Plasma membrane potential oscillations in insulin secreting Ins-1 832/13 cells do not require glycolysis and are not initiated by fluctuations in mitochondrial bioenergetics.
abstract: Oscillations in plasma membrane potential play a central role in glucose-induced insulin secretion from pancreatic β-cells and related insulinoma cell lines. We have employed a novel fluorescent plasma membrane potential (Δψ(p)) indicator in combination with indicators of cytoplasmic free Ca(2+) ([Ca(2+)](c)), mitochondrial membrane potential (Δψ(m)), matrix ATP concentration, and NAD(P)H fluorescence to investigate the role of mitochondria in the generation of plasma membrane potential oscillations in clonal INS-1 832/13 β-cells. Elevated glucose caused oscillations in plasma membrane potential and cytoplasmic free Ca(2+) concentration over the same concentration range required for insulin release, although considerable cell-to-cell heterogeneity was observed. Exogenous pyruvate was as effective as glucose in inducing oscillations, both in the presence and absence of 2.8 mM glucose. Increased glucose and pyruvate each produced a concentration-dependent mitochondrial hyperpolarization. The causal relationships between pairs of parameters (Δψ(p) and [Ca(2+)](c), Δψ(p) and NAD(P)H, matrix ATP and [Ca(2+)](c), and Δψ(m) and [Ca(2+)](c)) were investigated at single cell level. It is concluded that, in these β-cells, depolarizing oscillations in Δψ(p) are not initiated by mitochondrial bioenergetic changes. Instead, regardless of substrate, it appears that the mitochondria may simply be required to exceed a critical bioenergetic threshold to allow release of insulin. Once this threshold is exceeded, an autonomous Δψ(p) oscillatory mechanism is initiated.
authors.affiliation: Lund University Diabetes Centre, 20502 Malmö, Sweden.
authors.forename: Isabel
authors.initials: I
authors.lastname: Goehring
authors.forename: Akos A
authors.initials: AA
authors.lastname: Gerencser
authors.forename: Sara
authors.initials: S
authors.lastname: Schmidt
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
authors.forename: Hindrik
authors.initials: H
authors.lastname: Mulder
authors.forename: David G
authors.initials: DG
authors.lastname: Nicholls
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism; D005947:Glucose / Q000494:pharmacology; D006019:Glycolysis; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism* / Q000502:physiology; D019289:Pyruvic Acid / Q000494:pharmacology; D051381:Rats
chemical_list: D007328:Insulin; D019289:Pyruvic Acid; D000255:Adenosine Triphosphate; D005947:Glucose; D002118:Calcium