Liver glucose-6-phosphatase activity is modulated by physiological intracellular Ca2+ concentrations.
The effect of varying concentrations of free Ca2+ on the formation of Pi from mannose-6-P or of Pi and [U-14C]glucose from [U-14C]glucose-6-P was investigated in isolated fasted rat hepatocytes made permeable by freezing and in liver microsomes. Free Ca2+ concentration was adjusted by the use of Ca-EGTA buffers. In permeabilized cells, glucose-6-phosphatase (EC 3.1.3.9) activity was inhibited up to 50% and in intact microsomes up to 70% by increasing free Ca2+ concentrations from 0.01 to 10 microM. The inhibition was reversible and competitive with respect to glucose-6-P. Treatment of microsomes with 0.4% deoxycholate exposed 90% of latent mannose-6-phosphatase activity which was insensitive to Ca2+. The results indicate that Ca2+ affects the glucose-6-P translocase rather than the phosphohydrolase component. It is concluded that the glucose-6-phosphatase system is modulated by changes in Ca2+ concentrations in the range of those occurring in the liver cell upon hormonal stimulation.
van de Werve
G
G
Department of Nutrition, Faculty of Medicine, University of Montreal, Quebec, Canada.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D003840:Deoxycholic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008360:Mannosephosphates / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D012995:Solubility
D008360:Mannosephosphates; D003840:Deoxycholic Acid; C027693:mannose-6-phosphate; D004533:Egtazic Acid; D005952:Glucose-6-Phosphatase; D002118:Calcium