Fast, Na+/K+ pump driven, steady-state transcytolemmal water exchange in neuronal tissue

A study of rat brain cortical cultures

Ruiliang Bai, Charles Jr Springer, Dietmar Plenz, Peter J. Basser

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Purpose: Water homeostasis and transport play important roles in brain function (e.g., ion homeostasis, neuronal excitability, cell volume regulation, etc.). However, specific mechanisms of water transport across cell membranes in neuronal tissue have not been completely elaborated. Methods: The kinetics of transcytolemmal water exchange were measured in neuronal tissue using simultaneous, real-time fluorescence and nuclear magnetic resonance (NMR) measurements of perfused, active brain organotypic cortical cultures. Perfusion with a paramagnetic MRI contrast agent, gadoteridol, allows NMR determination of the unidirectional rate constant for steady-state cellular water efflux (kio), and the mole fraction of intracellular water (pi), related to the average cell volume (V). Changes in intracellular calcium concentration [Ca2+ i] were used as a proxy for neuronal activity and were monitored by fluorescence imaging. Results: The kio value, averaged over all cultures (N = 99) at baseline, was 2.02 (±1.72) s−1, indicating that on average, the equivalent of the entire intracellular water volume turns over twice each second. To probe possible molecular pathways, the specific Na+-K+-ATPase (NKA) inhibitor, ouabain (1 mM), was transiently introduced into the perfusate. This caused significant transient changes (N = 8): [Ca2+ i] rose ∼250%, V rose ∼89%, and kio fell ∼45%, with a metabolically active kio contribution probably eliminated by ouabain saturation. Conclusions: These results suggest that transcytolemmal water exchange in neuronal tissue involves mechanisms affected by NKA activity as well as passive pathways. The active pathway may account for half of the basal homeostatic water flux. Magn Reson Med 79:3207–3217, 2018.

Original languageEnglish (US)
Pages (from-to)3207-3217
Number of pages11
JournalMagnetic Resonance in Medicine
Volume79
Issue number6
DOIs
StatePublished - Jun 1 2018

Fingerprint

Water
Brain
Ouabain
Cell Size
Homeostasis
Magnetic Resonance Spectroscopy
Molecular Probes
Optical Imaging
Proxy
Contrast Media
Perfusion
Fluorescence
Cell Membrane
Ions
Calcium

Keywords

  • active
  • Na/K pump
  • neurons
  • ouabain
  • steady-state
  • transcytolemmal water exchange

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

Cite this

Fast, Na+/K+ pump driven, steady-state transcytolemmal water exchange in neuronal tissue : A study of rat brain cortical cultures. / Bai, Ruiliang; Springer, Charles Jr; Plenz, Dietmar; Basser, Peter J.

In: Magnetic Resonance in Medicine, Vol. 79, No. 6, 01.06.2018, p. 3207-3217.

Research output: Contribution to journalArticle

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abstract = "Purpose: Water homeostasis and transport play important roles in brain function (e.g., ion homeostasis, neuronal excitability, cell volume regulation, etc.). However, specific mechanisms of water transport across cell membranes in neuronal tissue have not been completely elaborated. Methods: The kinetics of transcytolemmal water exchange were measured in neuronal tissue using simultaneous, real-time fluorescence and nuclear magnetic resonance (NMR) measurements of perfused, active brain organotypic cortical cultures. Perfusion with a paramagnetic MRI contrast agent, gadoteridol, allows NMR determination of the unidirectional rate constant for steady-state cellular water efflux (kio), and the mole fraction of intracellular water (pi), related to the average cell volume (V). Changes in intracellular calcium concentration [Ca2+ i] were used as a proxy for neuronal activity and were monitored by fluorescence imaging. Results: The kio value, averaged over all cultures (N = 99) at baseline, was 2.02 (±1.72) s−1, indicating that on average, the equivalent of the entire intracellular water volume turns over twice each second. To probe possible molecular pathways, the specific Na+-K+-ATPase (NKA) inhibitor, ouabain (1 mM), was transiently introduced into the perfusate. This caused significant transient changes (N = 8): [Ca2+ i] rose ∼250{\%}, V rose ∼89{\%}, and kio fell ∼45{\%}, with a metabolically active kio contribution probably eliminated by ouabain saturation. Conclusions: These results suggest that transcytolemmal water exchange in neuronal tissue involves mechanisms affected by NKA activity as well as passive pathways. The active pathway may account for half of the basal homeostatic water flux. Magn Reson Med 79:3207–3217, 2018.",
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