Coupling of exocytosis to depolarization in rat pancreatic islet beta-cells: effects of Ca2+, Sr2+ and Ba(2+)-containing extracellular solutions.
Using rat beta-cells we present evidence that Sr2+ and Ba2+, like Ca2+, support depolarization-induced increases in membrane capacitance which reflect insulin granule exocytosis. Even with identical total charge entry, Sr2+ and Ba2+ are 3-5 and 20-fold less effective than Ca2+ in supporting release. While exocytosis supported by Sr2+ is graded with cation entry and complete within 250ms of depolarization, exocytosis supported by Ba2+ begins abruptly after a threshold of charge entry and continues for many seconds. Ba(2+)-supported release continues in the presence of greatly enhanced cytosolic Ca2+ buffering, arguing against release of Ca2+ from stores as its principal action. These results suggest that Sr2+ and Ba2+ support exocytosis largely by binding to Ca(2+)-dependent release-activating sites, though with less affinity than Ca2+.
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D003470:Culture Media; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D013324:Strontium / Q000494:pharmacology
D002413:Cations, Divalent; D003470:Culture Media; D001464:Barium; D002118:Calcium; D013324:Strontium