The stimulus-secretion coupling of glucose-induced insulin release. XXVIII. Effect of glucose on Na+ fluxes in isolated islets.
The effect of glucose upon the handling of 22Na+ by pancreatic islets was investigated. Using a triple-isotope technique, the apparent concentration of Na+ in islet cells was estimated at 50--75 mM. The pattern of 22Na+ efflux from perifused islets indicates that this intracellular Na+ load is compartmentalized among a small, possibly organelle-bound pool characterized by a low fractional turnover rate (5%/min) and a large, presumably cystosolic pool displaying a much higher fractional turnover rate (20--34%/min). Glucose provokes a rapid, pronounced and sustained increase in the fractional outflow rate of Na+ across the plasma membrane and, under steady-state conditions, moderately reduces the concentration of Na+ inside the islet cells. The glucose-induced increase in Na+ outflow rate, which is also observed in response to glyceraldehyde and dose not require the presence of extracellular Ca2+, might be mediated, in part at least, by an ouabain-resistant ionophoretic system. The experimental data suggest that glucose also increases the inward transport of Na+ in islet cells by a veratridine-sensitive channel.
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002414:Cations, Monovalent / Q000378:metabolism; D003600:Cytosol / Q000032:analysis; D005110:Extracellular Space / Q000032:analysis; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D005985:Glyceraldehyde / Q000494:pharmacology; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010477:Perfusion; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D002414:Cations, Monovalent; D005985:Glyceraldehyde; D010042:Ouabain; D014701:Veratridine; D012964:Sodium; D005947:Glucose; D002118:Calcium