Brain active transmembrane water cycling measured by MR is associated with neuronal activity

Abstract

These results suggest that AWC is associated with neuronal activity and NKA activity is a major contributor in coupling AWC to neuronal activity. Although AWC comprises steady-state, homeostatic transmembrane water exchange, our analysis also yields a simultaneous measure of the average cell volume, which reports any slower net transmembrane water transport.

Magnetic resonance measurements of cellular and sub-cellular membrane structures in live and fixed neural tissue

“…Results indicate that we have developed a non-invasive, sufficiently rapid method of measuring exchange across membranes in live tissue. The AXR ≈ 100 s −1 is significantly faster than intracellular-extracellular water exchange rates measured in neural tissue (≈ 0.5 − 5 s −1 ) (42,(89)(90)(91)(92). Such fast turnovers are not unheard of, e.g.…”

Progresses and prospects of brain electromagnetic imaging

“…tive transmembrane water exchange)可能是功能磁共振 能检测神经元活动的机制 [161] . 此外, 麻省理工学院的 研究人员设计出了一种基于磁共振成像的钙活性成像 方法 [162] , 该方法可以跟踪活体动物神经元内的信号传 导过程, 能够将神经活动与特定行为联系起来.…”

NMR shutter‐speed elucidates apparent population inversion of 1H2O signals due to active transmembrane water cycling

“…It was previously thought k io = k io (p): there was no active component. However, this is not the case: k io (a) is always present, and often dominant . It is elaborated as (x/([H 2 O i ]〈V〉)) c MR NKA , where c MR NKA is the cellular metabolic rate of the cell membrane Na + ,K + ‐ATPase (NKA) (fmol(ATP)hydrolyzed/cell/s), [H 2 O i ] is the intracellular water concentration, and x is the stoichiometric mole ratio of water actively cycled to ATP hydrolyzed by NKA [fmol(H 2 O)/fmol(ATP)].…”

“…This is important because NKA can be considered biology’s most vital enzyme, but its in vivo homeostatic activity has never been measurable or amenable to mapping . Significantly, it has been found that k io correlates with metastatic potential in breast and melanoma cell lines, and with neuronal firing in brain tissue . This is a new imaging biomarker with potentially great power.…”

“…This will be detailed below. Indeed, studies on model systems, in which constant [CA o ] ≥ 5 mM can be sustained during complete relaxation recovery measurement, were required to confirm the (x/([H 2 O i ]〈V〉)) c MR NKA term in Equation . However, this approach is problematic for in vivo human study …”