Evaluating the involvement of cerebral microvascular endothelial Na⁺/K⁺-ATPase and Na⁺-K⁺-2Cl^- co-transporter in electrolyte fluxes in an in vitro blood-brain barrier model of dehydration

TY - JOUR

T1 - Evaluating the involvement of cerebral microvascular endothelial Na+/K+-ATPase and Na+-K+-2Cl- co-transporter in electrolyte fluxes in an in vitro blood-brain barrier model of dehydration

AU - Lykke, Kasper

AU - Assentoft, Mette

AU - Hørlyck, Sofie

AU - Helms, Hans C. C.

AU - Stoica, Anca

AU - Toft-Bertelsen, Trine L

AU - Tritsaris, Katerina

AU - Vilhardt, Frederik

AU - Brodin, Birger

AU - MacAulay, Nanna

PY - 2019/3/1

Y1 - 2019/3/1

N2 - The blood-brain barrier (BBB) is involved in brain water and salt homeostasis. Blood osmolarity increases during dehydration and water is osmotically extracted from the brain. The loss of water is less than expected from pure osmotic forces, due to brain electrolyte accumulation. Although the underlying molecular mechanisms are unresolved, the current model suggests the luminally expressed Na+-K+-2Cl- co-transporter 1 (NKCC1) as a key component, while the role of the Na+/K+-ATPase remains uninvestigated. To test the involvement of these proteins in brain electrolyte flux under mimicked dehydration, we employed a tight in vitro co-culture BBB model with primary cultures of brain endothelial cells and astrocytes. The Na+/K+-ATPase and the NKCC1 were both functionally dominant in the abluminal membrane. Exposure of the in vitro BBB model to conditions mimicking systemic dehydration, i.e. hyperosmotic conditions, vasopressin, or increased [K+]o illustrated that NKCC1 activity was unaffected by exposure to vasopressin and to hyperosmotic conditions. Hyperosmotic conditions and increased K+ concentrations enhanced the Na+/K+-ATPase activity, here determined to consist of the α1 β1 and α1 β3 isozymes. Abluminally expressed endothelial Na+/K+-ATPase, and not NKCC1, may therefore counteract osmotic brain water loss during systemic dehydration by promoting brain Na+ accumulation.

AB - The blood-brain barrier (BBB) is involved in brain water and salt homeostasis. Blood osmolarity increases during dehydration and water is osmotically extracted from the brain. The loss of water is less than expected from pure osmotic forces, due to brain electrolyte accumulation. Although the underlying molecular mechanisms are unresolved, the current model suggests the luminally expressed Na+-K+-2Cl- co-transporter 1 (NKCC1) as a key component, while the role of the Na+/K+-ATPase remains uninvestigated. To test the involvement of these proteins in brain electrolyte flux under mimicked dehydration, we employed a tight in vitro co-culture BBB model with primary cultures of brain endothelial cells and astrocytes. The Na+/K+-ATPase and the NKCC1 were both functionally dominant in the abluminal membrane. Exposure of the in vitro BBB model to conditions mimicking systemic dehydration, i.e. hyperosmotic conditions, vasopressin, or increased [K+]o illustrated that NKCC1 activity was unaffected by exposure to vasopressin and to hyperosmotic conditions. Hyperosmotic conditions and increased K+ concentrations enhanced the Na+/K+-ATPase activity, here determined to consist of the α1 β1 and α1 β3 isozymes. Abluminally expressed endothelial Na+/K+-ATPase, and not NKCC1, may therefore counteract osmotic brain water loss during systemic dehydration by promoting brain Na+ accumulation.

KW - Blood–brain barrier

KW - brain water homeostasis

KW - dehydration

KW - ion transport

KW - volume regulation

U2 - 10.1177/0271678x17736715

DO - 10.1177/0271678x17736715

M3 - Journal article

C2 - 28994331

SN - 0271-678X

VL - 39

SP - 497

EP - 512

JO - Journal of Cerebral Blood Flow and Metabolism

JF - Journal of Cerebral Blood Flow and Metabolism

IS - 3

ER -