Fig. 10.

Addition of UTP to Ringer’s solution bathing the apical membrane elicited a significant increase in fluid absorption.A, The obligatory control-to-control solution change (see Materials and Methods) during the first 35 min produced very little change in J_v, TEP, andR_t. The initial, steady-stateJ_V was ∼1.0 μl · cm⁻² · hr⁻¹, indicating net absorption of fluid from the apical to basolateral chamber. The addition of 10 μm UTP (black bar) produced a transient increase inJ_V to ∼2.5 μl · cm⁻² · hr⁻¹, followed by a steady decrease to ∼1.5 μl · cm⁻² · hr⁻¹. The removal of UTP from the apical bathing solution brought J_V levels back down to ∼1.1 μl · cm⁻² · hr⁻¹.B, The addition of UTP produced electrical effects that were similar to those of ATP.