Do pancreatic islet cells from neonatal rats have surface receptors or sensors for divalent cations?
The effects of extracellular divalent cations on the intracellular Ca2+ concentration ([Ca2+]i) in neonatal rat islet cells were investigated to determine whether these cells, like several others, have signal-generating surface cation sensors. Raising the external Ca2+ concentration by 1 mM increments triggered either sustained increases in [Ca2+]i or large sharp [Ca2+]i spikes followed by return to a suprabasal level. The external Ca(2+)-triggered [Ca2+]i responses were abolished by treating the cells with the inhibitor of inositol phospholipid hydrolysis, neomycin (1.5 mM), but not by another phospholipase C inhibitor, U-73,122 (2.5 microM), or the voltage-sensitive Ca2+ channel blockers nifedipine (20 microM) and methoxyverapamil (D600; 50 microM). [Ca2+]i responses were also triggered by barium (Ba2+; 1 mM) and cobalt (Co2+; 1 mM). The Ba2+ responses were also inhibited by neomycin and unaffected by nifedipine or D600 and the Co2+ response required external Ca2+. Therefore, neonatal rat pancreatic islet cells may display divalent cation receptors/sensors on their surfaces. Activation of these putative receptors, which are coupled to neomycin-sensitive, voltage-independent, dihydropyridine-insensitive channels, by Ca2+, Ba2+ or Co2+ would trigger [Ca2+]i responses by opening these channels to admit external Ca2+ into the cell. The physiological function(s) of such cell-surface divalent cation receptors/sensors and the [Ca2+]i surges they generate in pancreatic islet cells is not known.
Division of Clinical Biochemistry, Ottawa General Hospital, Ontario, Canada.
J
J
Wang
P
P
Morley
N
N
Bégin-Heick
J F
JF
Whitfield
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology; D002478:Cells, Cultured; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2; D017136:Ion Transport; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002413:Cations, Divalent; D005456:Fluorescent Dyes; D011956:Receptors, Cell Surface; D002118:Calcium; D016257:Fura-2