Fig. 5.

Indirect evidence for a positive relationship between collecting duct cell volume, manipulated by different maneuvers in WT and P2Y₂−/− mice, and urinary ATP excretion. A: acute vasopressin V₂ receptor inhibition (V₂R-I) and acute oral water loading (WL) both increased urinary flow rate but induced opposite effects on urinary ATP excretion. Urinary flow rate is not a good predictor of urinary ATP excretion. For further details see the text. B: we propose that V₂R-I reduces CD water uptake and thus CD cell volume. In contrast, WL increases CD cell volume due to a reduction in extracellular tonicity. We propose that feedback regulation of cell volume via cell volume-induced ATP release is absent/reduced in P2Y₂−/− mice, resulting in greater ATP release. This influence is minimized by reducing water uptake by V₂R-I and maximized by WL-induced cell swelling. *P < 0.05 vs. basal. #P < 0.05 vs. WT. Based on and modified from Refs. 69 and 72.