Stretch activation of Ca2+ transients in pancreatic beta cells by mobilization of intracellular stores.
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.
Grapengiesser
Eva
E
Department of Medical Cell Biology, Uppsala University, Biomedicum, Uppsala, Sweden.
Gylfe
Erik
E
Dansk
Heléne
H
Hellman
Bo
B
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