Effect of dDAVP on basolateral cell surface water permeability in the outer medullary collecting duct

We report a novel approach for assessing the volume of living cells which allows quantitative, high-resolution characterization of dynamic changes in cell volume while retaining the cell functionality. The aim of this study was to evaluate the short-term effect of vasopressin on basolateral cell surface water permeability in the outer medullary collecting duct (OMCD). The permeability of the basolateral cell membrane was determined in the tubules where the apical membrane was blocked with oil injected into the lumen. The apparent coefficient of water permeability (P _f) was evaluated by measuring the cell swelling after the step from hypertonic to isotonic medium (600 mosm to 300 mosm). Desmopressin (dDAVP) induced an increase of the basolateral P _f from 113.7±8.5 μm/s in control cells to 186.6±11.4 μm/s in micro-dissected fragments of the OMCD incubated in vitro (10⁻⁷ M dDAVP, 30 min at 37 °C) (P<0.05). Mercury caused pronounced inhibition of basolateral water permeability (26.0±6.9 μm/s; P<0.05). The effect of mercury (1.0 mM HgCl₂) was reversible: after washing the fragments with PBS for 20 min, P _f values were restored to the control levels (125.0±9.5 μm/s). The results of the study indicate the existence of a mechanism controlling the osmotic water permeability of the basolateral cell membrane in the OMCD epithelium.