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The relationship between hydrogen ion secretion and the transport of other electrloytes was examined in the isolated urinary bladder of the water turtle. Symmetrical solutions which were free from exogenous carbon dioxide and bicarbonate bathed the two surfaces of the preparation, and the spontaneous electrical potential of the bladder was nullified by a voltage clamp. Active transport of sodium from mucosal to serosal medium was confirmed by simultaneous bidirectional flux measurements and found to be slightly, but not significantly, greater than the short-circuit current. In the absence of sodium in the bathing solutions, the normal potential difference across the bladder reversed and the current required to nullify this reversed potential difference had the same magnitude as the simultaneously measured rate of hydrogen ion secretion. The results indicate that, under these experimental conditions, the bladder transports sodium and hydrogen ion actively, but that chloride movement does not contribute to the short-circuit current. The rate of secretion of hydrogen ion was not affected by replacement of the sodium in the bathing media by cesium, or by inhibition of sodium transport by dinitrophenol. Acidification continued when chloride in the solutions was replaced by sulfate, or when potassium or calcium was removed from the solution bathing the mucosal surface. Secretion of hydrogen ion by the turtle bladder is not dependent on the simultaneous transport of other electrolytes across the bladder.

The electrical potential profile of the isolated toad bladder was examined in the spontaneously active, chronically short-circuited, and intermittently short-circuited states by means of glass micropipettes. The position of the micropipette tip within the bladder was evaluated by measuring the D.C. resistance between the micropipette tip and the reference electrode on the serosal side of the bladder. In the spontaneously active state, with concentrations of sodium in the mucosal solution ranging from less than 1 to 114 meq per liter, the potential profile consisted in the majority of impalements of two steps, each positive to the mucosal solution. A minority of impalements showed more than two potential steps, each positive to the mucosal solution. In the short-circuited state, the interior of the bladder was found to be negative to the bathing solution by approximately 5 mv. The results are interpreted as showing a potential step at the two surfaces of the epithelial cell layer of the toad bladder. In the spontaneously active state the potential change at the mucosal boundary is of the wrong polarity to bring about net sodium entry; the small electrical driving force across the mucosal surface which is present in the short-circuited state may contribute to the net entry of sodium from mucosal solutions with low sodium concentration.

The inward transport of potassium by separated dog erythrocytes has been studied at concentrations of potassium in the medium from 2.9 to 25.0 m.eq./liter and at 38.0 and 33.0 degrees C. At the physiological concentration of external potassium (4.06 m.eq./liter medium), the inward potassium flux is 0.11 m.eq./liter cells hour and the glucose consumption is 2.0 mM/liter cells hour. The dependence of potassium influx on extracellular potassium concentration is given by the following equation, K influx (m.eq./liter cells hour) = 0.028 [K](amb.) - 0.003 in which [K](amb.) refers to the potassium concentration in the medium. In a single 93 hour experiment, 94 per cent of the intracellular potassium was exchanged at an apparently uniform rate. The average apparent activation energy for the process is 7,750 calories +/- 2,000 calories/mol and there is some indication that the apparent activation energy of inward K transport decreases with increasing external K concentration.