Reevaluation of micropuncture techniques: some of the factors which affect the rate of fluid absorption by the proximal tubule.

The present study has shown: (1) Hydrostatic pressure from the lumen is not an effective driving force ofr fluid absorption (Jv). (2) Hydrostatic pressure from the contraluminal side can strongly inhibit Jv. (3) Colloid in the capillary perfusate can effectively minimize the artifact of capillary perfusion. (4) HCO3 free serum as capillary perfusate inhibited Jv approximately to 50% of control. (5) 5 mM NaCN in capillary perfusate (dialyzed serum) inhibited Jv by 90% after two min and almost totally after 4 min. The presence or absence of exogenous substrate in capillary perfusate had no effect on NC-induced inhibition. The data indicate that glycolysis alone can not sustain fluid absorption.