Transport and metabolism of glucose in isolated enterocytes of the black bullhead Ictalurus melas: Effects of diet and hormones

The uptake and metabolism of glucose were assessed in enterocytes isolated from black bullhead Ictalurus melas, The objective of this study was to exa mine the effects of diet and hormone treatment on glucose transport and met abolism, so the enterocyte was the most appropriate preparation, Glucose tr ansport was estimated using specific inhibitors: glucose uptake measured in the presence of phlorizin presumably represents transport at the basolater al membrane, whereas glucose uptake in the presence of cytochalasin B presu mably represents transport at the brush border, Feeding bullheads a standar d diet resulted in maximum enterocyte rates of glucose uptake of 438.2+/-35 .5 nmol mg(-1) cells h(-1) for transport in the presence of cytochalasin B and 427.0+/-49.7 nmol mg(-1) cells h(-1) (means +/- S.E.M., N=12) for trans port in the presence of phlorizin, These values represent 50 % of the total 3-O-methylglucose transported, The rate of transport in the presence of cy tochalasin B was increased in bullheads fed a high-carbohydrate diet, Incub ating bullhead enterocytes with glucagon or glucagon-like peptide-1 (GLP) a t 10(-8) mol l(-1) and with dexamethasone or isoproterenol at 10(-6) mol l( -1) significantly increased the rate of brush-border transport, but not the apparent affinity constant (Kt), Activation was dependent on hormone conce ntration, In contrast, insulin was without effect on transport rates, nor d id it counteract activation by glucagon-family peptides, CO2 production rat es from D-[C-14]glucose indicated that glucose metabolism was not limited b y transport rates in the enterocytes. Glucagon and GLP decreased maximal ox idation rates, whereas dexamethasone, isoproterenol and insulin did not alt er these rates, The activities of enterocyte hexokinase exceeded the rate o f glucose oxidation but not the rate of transport of glucose, at least at m aximum activities, implicating this enzyme as one component of the strategy to ensure that glucose is maximally available to the blood of this species .