TY - JOUR
T1 - Fast, Na+/K+ pump driven, steady-state transcytolemmal water exchange in neuronal tissue
T2 - A study of rat brain cortical cultures
AU - Bai, Ruiliang
AU - Springer, Charles S.
AU - Plenz, Dietmar
AU - Basser, Peter J.
N1 - Publisher Copyright:
© 2017 International Society for Magnetic Resonance in Medicine
PY - 2018/6
Y1 - 2018/6
N2 - 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.
AB - 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.
KW - Na/K pump
KW - active
KW - neurons
KW - ouabain
KW - steady-state
KW - transcytolemmal water exchange
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U2 - 10.1002/mrm.26980
DO - 10.1002/mrm.26980
M3 - Article
C2 - 29106751
AN - SCOPUS:85043360027
SN - 0740-3194
VL - 79
SP - 3207
EP - 3217
JO - Magnetic Resonance in Medicine
JF - Magnetic Resonance in Medicine
IS - 6
ER -