Datensatz

Zusammenfassung

Proximal inorganic phosphate (P_i) transport was evaluated using the standing droplet method with simultaneous microperfusion of the peritubular blood capillaries.
In chronic parathyroidectomized (PTX) rats addition of 3 μM of the Ca²⁺ ionophore A 23187 to the luminal perfusate had no effect on the P_i transport, although the isotonic fluid reabsorption was reduced by 20%. When the Ca²⁺ concentration in the perfusates was raised from 1.5 mM to 3.0 mM the reabsorption did not change significantly. But when Ca²⁺ was omitted from the perfusates the P_i reabsorption dropped by 19%, and when 2 mM EDTA were added to the perfusates P_i transport decreased by 35%.
The influx of P_i from the interstitial space and from the cell into the phosphate-free luminal perfusate did not change, when the perfusates were Ca²⁺-free, but it increased by 23% in the presence of 2 mM EDTA.
The data indicate that 1. a rise in intracellular Ca²⁺ above normal is not a factor which modifies “basal” P_i transport i.e. when P_i transport is independent of the action of parathyroid hormone. 2. A reduction of extracellular Ca²⁺ concentration from normal toward zero reduces P_i transport without changing the paracellular leak permeability for P_i. 3. With EDTA the paracellular leak permeability for P_i is increased, thus causing an even greater reduction in net P_i transport than with Ca²⁺-free solutions alone.