Spectral properties of the thick ascending limb
We used explicit calculations and numerical analysis to investigate spectral properties of NaCl transport in a mathematical model of the thick ascending limb (TAL) and tubuloglomerular feedback (TGF) mechanism. Explicit calculations predict that when the period of an oscillation in TAL luminal fluid flow evenly divides the steady-state fluid transit time of TAL, then the NaCl concentration in flow past the macula densa (MD ) maintains a value nearly equal to the steady-state concentration, i.e., there is a node at the MD. Oscillations with periods about half-way between nodal periods produce oscillations in NaCl concentration with locally maximal amplitude at the MD, i.e., they produce antinodes. These spectral properties were further evaluated by perturbing TAL model flow with broadband forcing and computing power spectra from numerical solutions of the closed-loop TGF signal. In cases where feedback gain is less than that required for emergence of a sustained oscillation, the spectra are dominated by the spectral structure of the TAL. Published measurements of power spectra of glomerular blood flow have characteristics consistent with the predicted spectral properties of the TAL.
Layton, HE; Pitman, EB; Moore, LC
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