Apical membrane endocytosis via coated pits is stimulated by removal of antidiuretic hormone from isolated, perfused rabbit cortical collecting tubule

Abstract

Antidiuretic hormone increases the water permeability of the cortical collecting tubule and causes the appearance of intramembrane particle aggregates in the apical plasma membrane of principal cells. Particle aggregates are located in apical membrane coated pits during stimulation of collecting ducts with ADH in situ. Removal of ADH causes a rapid decline in water permeability. We evaluated apical membrane retrieval associated with removal of ADH by studying the endocytosis of horseradish peroxidase (HRP) from an isotonic solution in the lumen. HRP uptake was quantified enzymatically and its intracellular distribution examined by electron microscopy. When tubules were perfused with HRP for 20 min in the absence of ADH, HRP uptake was 0.5 +/- 0.3 pg/min/micron tubule length (n = 6). The uptake of HRP in tubules exposed continuously to ADH during the 20-min HRP perfusion period was 1.3 +/- 0.8 pg/min/micron (n = 8). HRP uptake increased markedly to 3.2 +/- 1.1 pg/min/micron (n = 14), when the 20-min period of perfusion with HRP began immediately after removal of ADH from the peritubular bath. Endocytosis of HRP occurred in both principal and intercalated cells via apical membrane coated pits. We suggest that the rapid decline in cortical collecting duct water permeability which occurs following removal of ADH is mediated by retrieval of water permeable membrane via coated pits.