The effect of fasting on the potential difference across the brush‐border membrane of enterocytes in rat small intestine.

Abstract

SUMMARY1. The effects of starvation on the magnitude of the potential difference across the brush-border membrane of rat small intestine (Vm) have been studied in vitro.2. The mean values obtained for Vm in jejunal tissue after a fast of either 24 or 72 h duration (-53-5 and -55-0 mV respectively) were significantly greater than the mean value of -45-3 mV recorded using intestine from fed rats. A similar hyperpolarization was observed after a 72 h fast using intestine from a more distal region. The response to fasting seen in the jejunum appears to be caused by a decrease in Na+ permeability of the mucosal membrane.3. The addition ofD-galactose (4 mM) or L-valine (4 mM) to the mucosal fluid caused a depolarization of Vm. Using jejunum from fed animals, Vm in the presence of galactose and valine was found to be -403 and -39-2 mV respectively. Following a fast of 72 h duration, the values of Vm for the two substrates were -43-4 and -43-1 mV respectively. Phlorhizin (10-4 M) abolished the galactose-induced depolarization in both fed and fasted conditions but was without effect on the response to valine.4. It is concluded that starvation increases the electrical driving force for Na+ during Na+-coupled non-electrolyte transport into the enterocyte. The possible mechanisms involved in this adaptive response are discussed.

The role of cyclic AMP in the control of sugar transport across the brush‐border and basolateral membranes of rat jejunal enterocytes

“…The most likely explanation is that glucagon and cyclic AMP reduce the permeability of the mucosal membrane to Na+ while the permeability of the membrane to K+ and Cl-remain unaltered. This phenomenon is well recognized in a number of situations where VJ' is increased, for example, fasting (Debnam & Thompson, 1984), chronic glucagon treatment (Thompson & Debnam, 1986), diabetes (Debnam & Ebrahim, 1989) and chronic exposure of the intestine to ethanol (Al-Balool, Debnam & Mazzanti, 1989). The response shown by cyclic AMP to changes in [Na+] was enhanced when jejunal segments were co-incubated with IBMX, suggesting that a large fraction of the cyclic AMP that crossed the cell membrane was broken down by phosphodiesterase activity before it could exert an effect on VJ.…”

“…In other experiments IBMX (1 mM) was present with, or in place of, cyclic AMP. Measurement of Vm V. was measured as described previously (Debnam & Thompson, 1984) …”

Bile Acid Uptake via the Human Apical Sodium-Bile Acid Cotransporter Is Electrogenic

“…Secondly, electrogenicity of uptake provides a means for regulation of transport. Fasting (34), aldosterone (34), and 5-hydroxytryptamine (35) have all been shown to alter intestinal electrical gradients in the direction of hyperpolarization of the brush border membrane. These physiologic changes may provide the ileal intestinal cells with a mechanism to regulate bile acid uptake rates for optimal bile acid recycling and cytoprotection.…”

The effect of rapid changes in plasma sugar concentration on the brush‐border potential difference in rat jejunum

“…It is likely that the higher PD noted in jejunal enterocytes of diabetic (Debnam, Karasov & Thompson, 1988;Debnam & Ebrahim, 1989), fasted (Debnam & Thompson, 1984) rats and both acutely (Sharp & Debnam, 1994) and chronically glucagon-treated animals (Thompson & Debnam, 1986) contributes to the increased sugar uptake seen in these conditions.…”

“…During the above procedures, body temperature was maintained at 37°C using a heating blanket (Harvard Apparatus Ltd, Edenbridge, UK). Measurement of PD PD was measured as described previously (Debnam & Thompson, 1984). In brief, a 1 cm section of isolated jejunum was cut longitudinally and mounted as a flat sheet on a Perspex disc using cyanoacrylate adhesive applied to the muscle side.…”