Cytoplasmic Ca2+ in glucagon-producing pancreatic alpha-cells exposed to carbachol and agents affecting Na+ fluxes.
The cytoplasmic Ca2+ concentration ([Ca2+]i) was measured with dual wavelength fluorometry in glucagon-producing mouse pancreatic alpha-cells loaded with the indicator fura-2. Spontaneous rhythmic activity in terms of slow oscillations from a basal level was observed at 3 mM glucose. Like in the insulin-secreting beta-cells the generation of [Ca2+]i oscillations in the alpha-cells was affected by the activity of the Na/K pump. Blocking the pump with ouabain resulted in an initial rise of [Ca2+]i followed by gradual return to the basal level. The oscillations were transformed into sustained elevation of [Ca2+]i by 10 mM L-glycine, which is cotransported with Na+. A similar but less pronounced effect was obtained when Na+ was cotransported with 10 mM of the nonmetabolizable amino acid alpha-amino-isobutyric acid. L-glycine induced sustained increase of [Ca2+]i also when the oscillatory activity was suppressed by exposing the alpha-cells to 20 mM glucose in the presence of insulin. The observation that carbachol induces a [Ca2+]i response in isolated alpha-cells calls for reconsideration of current ideas that muscarinic stimulation of glucagon release is an indirect effect mediated by adjacent beta-cells.
Berts
A
A
Department of Medical Cell Biology, Uppsala University, Sweden.
Gylfe
E
E
Hellman
B
B
D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology*; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2; D005934:Glucagon / Q000096:biosynthesis*; D005998:Glycine / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018721:Muscarinic Agonists / Q000494:pharmacology*; D015398:Signal Transduction / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D000621:Aminoisobutyric Acids; D005456:Fluorescent Dyes; D018721:Muscarinic Agonists; D015222:Sodium Channels; C100049:2-aminoisobutyric acid; D002217:Carbachol; D005934:Glucagon; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium; D005998:Glycine; D016257:Fura-2