title: Stretch activation of Ca2+ transients in pancreatic beta cells by mobilization of intracellular stores.
abstract: BACKGROUND
  Nonadrenergic, noncholinergic neurons have been proposed to synchronize pulsatile insulin release from the islets in the pancreas by triggering transient increases of the cytoplasmic Ca2+ concentration ([Ca2+]i) in beta-cells via an inositol trisphoshate-dependent mechanism.
  
  
  OBJECTIVE
  To test whether pancreatic beta-cells respond to stretch activation with similar types of transients and whether these Ca signals propagate to other beta-cells in the presence and absence of cell contacts.
  
  
  METHODS
  Single cells and small aggregates were prepared from beta-cell-rich islets from mice. After 2-5 days of culture, [Ca2+]i was measured with digital imaging and the indicator fura-2 during superfusion with a medium containing 20 mmol/L glucose and 50 micromol/L methoxyverapamil. Membrane stretch was induced by osmotic swelling or focal touch stimulation.
  
  
  RESULTS
  Lowering the medium osmolarity with 100-102 mOSM/L by removal of sucrose or by dilution resulted in a 2-3-fold increase in the number of transients during an initial 5-minute period. Sucrose omission was stimulatory also after isosmolar replacement with readily penetrating urea. The intracellular Ca2+-ATPase inhibitor thapsigargin suppressed both the spontaneously occurring transients and those initiated by volume expansion. Touch stimuli induced [Ca2+]i transients, which rapidly propagated to cells within the same aggregate or lacking contact.
  
  
  CONCLUSIONS
  The observations support the idea that beta-cells both receive and regenerate extracellular signals triggering [Ca2+]i transients. Touch stimulation is a useful tool for investigating the propagation of [Ca2+]i signals between pancreatic beta-cells lacking physical contact.
authors.affiliation: Department of Medical Cell Biology, Uppsala University, Biomedicum, Uppsala, Sweden.
authors.forename: Eva
authors.initials: E
authors.lastname: Grapengiesser
authors.forename: Erik
authors.initials: E
authors.lastname: Gylfe
authors.forename: Heléne
authors.initials: H
authors.lastname: Dansk
authors.forename: Bo
authors.initials: B
authors.lastname: Hellman
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D002450:Cell Communication; D002478:Cells, Cultured; D007515:Islets of Langerhans / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008820:Mice, Obese; D009994:Osmolar Concentration; D010507:Periodicity; D013314:Stress, Mechanical