Store-operated Ca2+ entry in insulin-releasing pancreatic beta-cells

Cell Calcium. 1997 Oct;22(4):277-86. doi: 10.1016/s0143-4160(97)90066-x.

Abstract

The fluorescent indicator Fura-2 was used to characterize the store-operated Ca2+ entry in insulin-releasing pancreatic beta-cells. To avoid interference with voltage-dependent Ca2+ entry, the cells were hyperpolarized with 400 microM diazoxide and the channel blocker methoxyverapamil was also present in some experiments. The cytoplasmic Ca2+ concentration ([Ca2+]j) of hyperpolarized mouse beta-cells was strikingly resistant to changes in external Ca2+. In cells exposed to 20 mM glucose, stimulation with 100 microM carbachol induced an initial [Ca2+]j peak followed by a sustained increase due to store-operated influx of the cation. Store-operated influx was also induced by the intracellular Ca(2+)-ATPase inhibitor thapsigargin. In the presence of store-operated influx, [Ca2+]j became markedly sensitive to variations in external Ca2+, but this sensitivity was blocked by La3+. In beta-cells exposed to both Ca2+ and Mn2+ there was slow Mn2+ quenching of the Fura-2 fluorescence, which was accelerated upon stimulation of store-operated influx. This acceleration was reversed by glucose-stimulated filling of the internal Ca2+ stores. The store-operated Ca2+ entry increased markedly during culture of the beta-cells. Activation of protein kinase C by the phorbol ester 12-O-tetradecanoylphorbol-13 acetate, inhibition of serine/threonine phosphatase by okadaic acid and inhibition of tyrosine kinase by genistein had little effect on the store-operated influx of Ca2+. In beta-cells equilibrated in 5 mM Sr2+, carbachol exposure resulted in a pronounced cytoplasmic Sr2+ ([Sr2+]j) peak due to intracellular mobilization, but little or no sustained elevation. Moreover, after activating the store-operated pathway by exposure to thapsigargin, variations in extracellular Sr2+ between 0-2 mM had only marginal effects on [Sr2+]j. Although the store-operated influx apparently accounts for a minor fraction of the Ca2+ entry, its depolarizing influence may under certain conditions be up-regulated with resulting distortion of the beta-cell function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calcium / pharmacology
  • Calcium Channel Blockers / pharmacology
  • Calcium-Transporting ATPases / antagonists & inhibitors
  • Carbachol / pharmacology
  • Cells, Cultured
  • Enzyme Inhibitors / pharmacology
  • Fluorescent Dyes / metabolism
  • Fura-2 / metabolism
  • Gallopamil / pharmacology
  • Genistein / pharmacology
  • Insulin / metabolism*
  • Islets of Langerhans / cytology
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / metabolism*
  • Lanthanum / pharmacology
  • Manganese / metabolism
  • Manganese / pharmacology
  • Mice
  • Mice, Obese
  • Okadaic Acid / pharmacology
  • Pancreas / cytology
  • Phosphoprotein Phosphatases / antagonists & inhibitors
  • Protein-Tyrosine Kinases / antagonists & inhibitors
  • Strontium / metabolism
  • Strontium / pharmacology
  • Tetradecanoylphorbol Acetate / pharmacology
  • Thapsigargin / pharmacology
  • Time Factors

Substances

  • Calcium Channel Blockers
  • Enzyme Inhibitors
  • Fluorescent Dyes
  • Insulin
  • Okadaic Acid
  • Gallopamil
  • Manganese
  • Thapsigargin
  • Lanthanum
  • Carbachol
  • Genistein
  • Protein-Tyrosine Kinases
  • Phosphoprotein Phosphatases
  • Calcium-Transporting ATPases
  • Tetradecanoylphorbol Acetate
  • Calcium
  • Fura-2
  • Strontium