Regulation of Sodium Transport in A6 Epithelia by Prostaglandin E(2)

86 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1999.A pulse method of blocker-induced noise analysis was used to study the time-dependent changes of channel density (NT), channel open probability (Po) and single-channel current (iNa) of apical membrane epithelial Na + channels (ENaCs) in A6 epithelia in response to 1 muM PGE 2 added to the basolateral solution. Epithelia were investigated in both unstimulated (n = 11) and aldosterone-stimulated states of Na + transport (n = 8) where changes of transport measured as amiloride-sensitive short-circuit currents (INa) could be decomposed into the underlying time-dependent changes of iNa, Po and NT. After a short delay of about 1 min, INa increased to maximum values within approximately 17 min (6.4 +/- 0.6 to 16.5 +/- 1.0 muA/cm 2 in unstimulated tissues; 18.0 +/- 1.7 to 26.5 +/- 2.1 muA/cm 2 in aldosterone-stimulated tissues). Increases of transport and decreases of single-channel current from mean values of 0.40 +/- 0.01 to 0.24 +/- 0.02 pA in unstimulated tissues and from 0.37 +/- 0.01 to 0.23 +/- 0.02 pA in aldosterone-stimulated tissues mandated mean increases of open channel density No = P oNT of 355 +/- 44% and 161 +/- 28% in unstimulated and aldosterone-stimulated tissues, respectively, at 17 min following PGE2 treatment. The increases of open channel density from baseline values of 18.4 +/- 1.4 (unstimulated) and 52.9 +/- 4.5 (aldosterone-stimulated) channels/100mum2 were due to increases of the functional channel densities (NT) but were accompanied by a transient decrease of Po only in tissues that were prestimulated with aldosterone. Zero time control values of Po averaged 0.52 +/- 0.05 and 0.51 +/- 0.05 in unstimulated and aldosterone-stimulated tissues, respectively, and decreased transiently in aldosterone-stimulated tissues at 7 min to 0.25 +/- 0.05, with return to 0.53 +/- 0.07 at 17 min. Thereafter, P o decreased slowly in unstimulated and stimulated tissues to 0.38 +/- 0.04 and 0.27 +/- 0.05, respectively, about two hours after treating the tissues with PGE2. From measured increases of N T of 476 +/- 47% in unstimulated tissues at 17 min and 373 +/- 69% in stimulated tissues at 7 min, NT underwent a secondary transient decrease remaining however, well above zero time control values for the duration of the 2 h experimental periods. Accordingly, PGE 2 stimulates Na+ transport in A6 epithelia both acutely and chronically by increase of the density of functional ENaCs at the apical membranes of these cells.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD