title: The effect of fasting on the potential difference across the brush-border membrane of enterocytes in rat small intestine.
abstract: 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. 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. The addition of D-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 -40.3 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. 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.
mesh_terms: D000818:Animals; D005215:Fasting; D005690:Galactose / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007082:Ileum / Q000502:physiology; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000502:physiology*; D007583:Jejunum / Q000187:drug effects / Q000502:physiology; D008297:Male; D008353:Mannitol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008871:Microvilli / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D014633:Valine / Q000494:pharmacology
chemical_list: D008353:Mannitol; D012964:Sodium; D014633:Valine; D005947:Glucose; D011188:Potassium; D005690:Galactose