We show that if a metabolic intermediate is directly transferred ('channelled') from an enzyme that catalyses its production to another that uses it as substrate, there is no change in its free concentration compared with a system with the same net flux in which there is no direct transfer. Thus the widespread idea that channelling provides a mechanism for decreasing metabolite concentrations a...

The effects of both an H1 receptor antagonist and an H2 receptor antagonist on changes in monovalent ion flux induced by topical sodium taurocholate were studied in antrectomised dogs fashioned with a denervated fundic pouch. The magnitude of taurocholate-induced ion flux was unaffected by topical administration of H1 or H2 receptor antagonists Parenteral administration of H1 or H2 receptor ant...

The flux ratio of potassium ions was measured on frog sartorius muscle under conditions in which a substantial net potassium loss occurs. Muscle fiber membrane potentials were measured under identical conditions. The observed flux ratios were compared with values calculated from a theoretical relation derived on the assumptions that the unidirectional fluxes are both passive and occur independe...

Intestinal oxalate transport, mediated by anion exchange proteins, is important to oxalate homeostasis and consequently to calcium oxalate stone diseases. To assess the contribution of the putative anion transporter (PAT)1 (Slc26a6) to transepithelial oxalate transport, we compared the unidirectional and net fluxes of oxalate across isolated, short-circuited segments of the distal ileum of wild...

The effect of increased hydrostatic pressure in the peritubular vessels on net sodium reabsorption from the proximal tubule was examined in the Necturus. An increase in the pressure gradient of 2.0 cm H(2)O across the wall of the proximal tubule, produced by ligation of the postcaval vein was associated with a marked reduction in net reabsorption and an increased back flux of water and electrol...

The global carbon cycle is part of the much more extensive sedimentary cycle that involves large masses of carbon in the Earth’s inner and outer spheres. Studies of the carbon cycle generally followed a progression in knowledge of the natural biological, then chemical, and finally geological processes involved, culminating in a more or less integrated picture of the biogeochemical carbon cycle ...