The rat small intestine has the capacity to transfer a number of substances, including hexoses, inorganic salts and fluid. Riklis & Quastel (1958) showed that movement of hexose was dependent on the presence of sodium, and Barry, showed that a part of the fluid transfer was dependent on the presence of glucose, and part was independent of it. It is generally assumed that fluid movement in living tissues is related to movement of inorganic salts, and there must therefore be a complex inter-relation between transfer of sodium, glucose and fluid. Since electrical changes in other tissues are related to ion pumps, an investigation was undertaken into the relation between the electrical potential across the wall of the intestine and the transfer of fluid, various ions, hexoses and their derivatives. The present paper deals with transfer of fluid and sugars in relation to electrical changes, and preliminary communications of the results have been given by Barry, Dikstein, Matthews & Smyth (1961), and Barry, Matthews, Smyth & Wright (1962).
METHODSWhite male rats of the Sheffield strain were used. Before experiments the rats were maintained on an unrestricted diet of rat cubes No. 86 (Oxoid, London). The work included three different kinds of experiments: (1) the effect of hexoses on the electrical potential difference across the gut wall, and this was studied both in vitro and in vivo; (2) determination of the rate of fluid transfer maintained by different sugars or their derivatives; and (3) the extent of metabolism of these sugars by the intestine: these last two were studied by in vitro methods. In the in vitro experiments the intestine was suspended in bicarbonate saline (Krebs & Henseleit, 1932), which was in equilibrium with a gas mixture of 5 % CO2 and 95 % 02-When anoxic conditions were required a gas mixture of 5 % CO2 and 95 % N2 was used.Measurement of electrical potentials across intestine Electrical recording. The potentials were led off from the solutions on each side of the gut wall to calomel half-cells by means of polythene tubes filled with M-KCI-3 %-agar, and these tubes are referred to subsequently as salt bridges. The pairs of calomel half-cells were selected to balance each other to within 1 mV. The half-cells were connected with a Hewlett-Packard vacuum tube voltmeter, with a minimum input impedance of 10 MO.