Transient renal responses to close arterial instantaneous injections of NaH2PO4 and creatinine ( ca. 500 µmoles of each) were studied in dogs under conditions of high urine flow with ‘normal’ (0.5–1 mm/l.), and with high (3–5 mm/l.) levels of serum phosphate. When serum phosphate was at normal levels (no exogenously administered phosphate), the increment of phosphate excretion per unit injected per one circulation of injected substance was equal to or less than that of creatinine. When serum phosphate was elevated (by continuous infusion of NaH2PO4 for 1 hr. preceding injection), the increment of phosphate excretion per unit injected per one circulation exceeded that of creatinine. Such findings suggested the existence of a tubular secretory mechanism for phosphate. Dependency of the postulated mechanism upon cellular reserves and/or plasma concentration of phosphate is discussed.
Sodium phosphate and creatinine (500 µmoles each) were injected instantaneously into the renal artery of dogs anesthetized with Nembutal. Urine flows of 6–12 ml/min and serum phosphate levels of 3–6 mm/liter were maintained for 1 hr preceding instantaneous injection. Dogs were divided into two major groups, based on steady state conditions imposed: a) systemic acidosis induced by infusion of NaH2PO4 and b) systemic alkalosis induced by infusion of Na2HPO4 + NaHCO3. Then, either NaH2PO4 or Na2HPO4 was injected close-arterially, and the transient excretory response (covering 3–5 min) was studied. The parameter for measuring renal function was the incremental excretion of phosphate per unit injected per one circulation through the kidney. This was compared to the simultaneous and identical parameter for creatinine, considered as a glomerular substance. During systemic acidosis, net transient secretion of phosphate was observed in 73% of the periods after H2PO4– injection, and in 19% of the periods after HPO4– injection into renal artery. During systemic alkalosis with formation of alkaline urine, net secretion was observed in 15% of the periods after HPO4– injection, and in none of the periods after H2PO4– injection into the renal artery. When paradoxical aciduria occurred during systemic alkalosis, net transient secretion was observed in 30% of the periods after HPO4– injection. Data show that the transtubular movement of H2PO4– ion is different from that of HPO4– ion. The possibility of tubular secretion of H2PO4– ion, as a mechanism of urine acidification, is discussed.
Amiloride, a pyrazine diuretic, has been shown to decrease the secretion of K+ by the renal tubule (1-3). Although this effect has been explained as a result of the inhibitory aation of the drug on Na+ reabsorption, the possibility exists that amiloride might directly affect K+ permeability. This thought led to the speculation that amiloride might likewise affect the K+ permeability of the frog gastric mucosa which lends itself well to such an investigation. From the literature (4, S ) , it appears that the K+ resistance of the nutrient membrane of frog gastric mucosa is about half the C1-resistance and that other ionic resistances are very high relative to the K+ and C1-resistances.Since K + has been found to be essential for HCl secretion (6), perhaps if amiloride affected the K+ permeability it might also decrease the H+ secretory rate. Experiments were, therefore, designed to test the effect of arniloride on the transmembrane resistance, the transmembrane potential difference (PD), and the H-+ secretory rate in high and low nutrient K + -solutions.Methods. The experiments were performed on gastric mucosae of Rana pipiens with an in vitro method described in detail elsewhere ( 7 ) . In this method each mucosa was mounted between cylindrical chambers. Two pairs of electmodes were used, one for sending current across the mucosla and the other for measuring the PD. The resistance was determined as the change in PD per unit of applied current. The nutrient bathing solution contained ( m u ) : Na+, 101; K+, 4; Ca2+, 1; Mg2+, 0.8; C1-, 81; HC03-, 25; phosphate, 1.0; and glucose, 10; and the secretory bathing solution: Na+, 102; K+, 4; C1-, 106. In high K+ nutrient solutions, K+ replaced Na+, B~t h sides of the mucosa were gassed with 95% O2 and 5% C02.The pH of the secretory solution was maintained at 4.90. After the control part of the experiment, amiloride was added in the nutrient solution to a 0.5 or 2.0 mM concentra tion.Results. Figure 1 shows the effects of adding amiloride to the nutrient solution. At the time indicated by the arrow, amiloride was added to a concentration of 0.5 mM in the nutrient solution. A comparison was generally made of the changes in the parameters in about 30 min following the addition of amilorirde in the nutrient solution to the control values just before the addition. As shown in Fig. 1, the resistance inlcreased about SO%, the PD decreased about 15%, and the H+ rate decreased about 30%. Washing both sides of the mucosa with regular solutions produced only a partial recovery of the parameters towards control values. In about 40% of the experiments after washing with regular solutions, the resistance decreased to some extent towards control values while the H+ rate persisted at about the same level as with amiloride in the nutrient solution. Table I sulmmarizes the main results. Columns 111, V and VII give, respectively, the average resistances, PD and H+ rates of mucosae bathed in regular solutions without amiloride. Columns IV, VI and VIII give, respectively, the average percentag...
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