Mechanism of Aldosterone Regulation of Sodium Transport in A6 Epithelia

81 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1998.The mineralocorticoid hormone, aldosterone, is known to stimulate Na$\sp+$ transport in tight epithelia. The goal of this dissertation was to study the mechanism of aldosterone stimulation of Na$\sp+$ transport through amiloride-sensitive Na' channels (ENaCs) in cell cultured A6 epithelia. Non-invasive methods of blocker-induced noise analysis were used to investigate the way aldosterone changes the single channel current $(i\sb{Na}),$ open probability $(P\sb{o})$ and channel density $(N\sb{T})$ of ENaCs at the apical membranes of the epithelial cells. Two groups of experiments were done to evaluate (1) the chronic changes in transport in A6 epithelia treated overnight with aldosterone and (2) the early transient changes in transport that occur within 6 hours after exposure of tissues to aldosterone. The overnight effects of aldosterone were studied using a staircase blocker-induced method of noise analysis. We found that the increase in the macroscopic amiloride-sensitive current $(I\sb{Na})$ measured as the short-circuit current after overnight aldosterone treatment was due to an increase in $N\sb{T}.$ The early effects of aldosterone were investigated using a pulse protocol blocker-induced method of noise analysis that permitted analysis during transient conditions of transport and where each tissue served as its own control. After a delay of about 60-90 minutes in tissues with markedly different mean baseline rates of transport (1.06 to 15.14 $\mu$A/cm$\sp2),$ the early time-dependent increases in IN, caused by aldosterone were also due to increases in $N\sb{T}$ with little or no change of $I\sb{Na}$ or $P\sb{o}.$ Therefore, at least within 24 hours and independent of baseline differences in the rates of Na$\sp+$ transport, the aldosterone-stimulated increase in Na$\sp+$ transport could be attributed to increases in the density of the functional pool of channels, $N\sb{T},$ responsible for entry of Na$\sp+$ into the cells at their apical membranes.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD