Transmembrane Exchange of Hyperpolarized 13C-Urea in Human Erythrocytes: Subminute Timescale Kinetic Analysis

• Published in: Biophysical journal Vol. 105; no. 9; pp. 1956 - 1966
• Main Authors: Pagès, Guilhem, Puckeridge, Max, Liangfeng, Guo, Tan, Yee Ling, Jacob, Chacko, Garland, Marc, Kuchel, Philip W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 05.11.2013; Biophysical Society; The Biophysical Society
• Subjects: Analytical chemistry; Carbon Isotopes; Cell Biophysics; Chemical Sciences; equations; Erythrocyte Membrane - metabolism; erythrocytes; Humans; Kinetics; Markov chain; Membrane Transport Proteins - metabolism; Models, Biological; Monte Carlo method; nuclear magnetic resonance spectroscopy; urea; Urea - chemistry; Urea - metabolism; Urea Transporters
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2013.09.034

The rate of exchange of urea across the membranes of human erythrocytes (red blood cells) was quantified on the 1-s to 2-min timescale. 13C-urea was hyperpolarized and subjected to rapid dissolution and the previously reported (partial) resolution of 13C NMR resonances from the molecules inside and outside red blood cells in suspensions was observed. This enabled a stopped-flow type of experiment to measure the (initially) zero-trans transport of urea with sequential single-pulse 13C NMR spectra, every second for up to ∼2 min. Data were analyzed using Bayesian reasoning and a Markov chain Monte Carlo method with a set of simultaneous nonlinear differential equations that described nuclear magnetic relaxation combined with transmembrane exchange. Our results contribute to quantitative understanding of urea-exchange kinetics in the whole body; and the methodological approach is likely to be applicable to other cellular systems and tissues in vivo.