부산대학교 도서관

Nieves-Gonzalez A, Clausen C, Layton AT, Layton HE, Moore LC. Transport efficiency and workload distribution in a mathematical model of the thick ascending limb. Am J Physiol Renal Physio1 304: F653--F664, 2013. First published October 24, 2012; doi:10.1152/ajprenal.00101.2012.--The thick ascending limb (TAL) is a major NaCl reabsorbing site in the nephron. Efficient reabsorption along that segment is thought to be a consequence of the establishment of a strong transepithelial potential that drives paracellular [Na.sup.+] uptake. We used a multicell mathematical model of the TAL to estimate the efficiency of [Na.sup.+] transport along the TAL and to examine factors that determine transport efficiency, given the condition that TAL outflow must be adequately dilute. The TAL model consists of a series of epithelial cell models that represent all major solutes and transport pathways. Model equations describe luminal flows, based on mass conservation and electroneutrality constraints. Empirical descriptions of cell volume regulation (CVR) and pH control were implemented, together with the tubuloglomerular feedback (TGF) system. Transport efficiency was calculated as the ratio of total net [Na.sup.+] transport (i.e., paracellular and transcellular transport) to transcellular [Na.sup.+] transport. Model predictions suggest that 1) the transepithelial [Na.sup.+] concentration gradient is a major determinant of transport efficiency; 2) CVR in individual cells influences the distribution of net [Na.sup.+] transport along the TAL; 3) CVR responses in conjunction with TGF maintain luminal [Na.sup.+] concentration well above static head levels in the cortical TAL, thereby preventing large decreases in transport efficiency; and 4) under the condition that the distribution of [Na.sup.+] transport along the TAL is quasi-uniform, the tubular fluid axial [Cl.sup.-] Concentration gradient near the macula densa is sufficiently steep to yield a TGF gain consistent with experimental data. tubuloglomerular feedback; autoregulation; NaCl transport; cell volume regulation