Study of Chloride Transport Across the Rabbit Cortical Collecting Tubule

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Abstract

Recent micropuncture studies have suggested that the collecting tubule may be involved in the regulation of extracellular fluid volume. The present studies were designed to evaluate chloride transport across the in vitro-perfused rabbit cortical collecting tubule inasmuch as chloride ion would ultimately affect extracellular fluid volume. The tubules were perfused and bathed with artificial solutions simulating ultrafiltrate. Four groups of studies were conducted. In groups one and two, tubules from rabbits not receiving desoxycorticosterone (DOCA) were compared to tubules from rabbits which had received DOCA (5 mg/day) for 1 wk. In groups three and four, tubules were obtained only from rabbits not receiving DOCA. In group one, sequential bidirectional chloride fluxes were measured. The ratio of chloride efflux to influx was 0.99±0.04 in tubules obtained from rabbits not receiving DOCA whereas it was 1.28±0.09 in tubules obtained from rabbits receiving DOCA, suggesting stimulation of net chloride flux under these conditions. In group 2, chemical chloride concentration and osmolality of the collected fluid were measured. Neither the chemical chloride concentration nor the osmolality of the collected fluid decreased significantly below their respective perfusion fluid values in tubules from non-DOCA-treated rabbits but there was a significant decrease in the chemical chloride concentration (10-42 meq/liter) and osmolality (10-42 mosmol/kg H2O of the collected fluid in tubules from DOCA-treated rabbits. In group three, unidirectional chloride permeabilities from lumen-to-bath were determined during the passage of current down the perfusion pipette. The alterations of the average lumen potential, −35±4 and +28±2 mV, did not influence unidirectional chloride movement suggesting that the cortical collecting tubule is quite impermeable to chloride. In group four, unidirectional chloride permeability from lumen-to-bath was measured before and after substitution of NaCH3SO4 for sodium chloride in the bath. Replacement of chloride by CH3SO4 reversibly decreased the apparent chloride permeability from 2.41±0.50 to 0.69±0.08 (×10−5 cm/s) demonstrating that 36Cl permeability is dependent on the chemical concentration of chloride.

Authors

Michael J. Hanley, Juha P. Kokko