Stimulant-evoked depolarization and increase in [Ca2+] i in insulin-secreting cells is dependent on external Na+ |
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Authors: | M. J. Dunne D. I. Yule D. V. Gallacher O. H. Petersen |
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Affiliation: | (1) MRC Secretory Control Research Group, Department of Physiology, University of Liverpool, L69 3BX Liverpool, England |
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Abstract: | Summary The patch-clamp technique and measurements of single cell [Ca2+]i have been used to investigate the importance of extracellular Na+ for carbohydrate-induced stimulation of RINm5F insulin-secreting cells. Using patch-clamp whole-cell (current-clamp) recordings the average cellular transmembrane potential was estimated to be –60±1 mV (n=83) and the average basal [Ca2+]i 102±6nm (n=37). When challenged with either glucose (2.5–10mm) ord-glyceraldehyde (10mm) the cells depolarized, which led to the initiation of Ca2+ spike potentials and a sharp rise in [Ca2+]i. Similar effects were also observed with the sulphonylurea compound tolbutamide (0.01–0.1mm). Both the generation of the spike potentials and the increase in [Ca2+]i were abolished when Ca2+ was removed from the bathing media. When all external Na+ was replaced with N-methyl-d-glucamine, in the continued presence of either glucose,d-glyceraldehyde or tolbutamide, a membrane repolarization resulted, which terminated Ca2+ spike potentials and attenuated the rise in [Ca2+]i. Tetrodotoxin (TTX) (1–2 m) was also found to both repolarize the membrane and abolish secretagogue-induced rises in [Ca2+]i. |
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Keywords: | patch clamp [Ca2+]i Na+ dependency RINm5F cell fura-2 whole cell |
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