Blood–Brain Barrier KCa3.1 Channels

Abstract

Background and Purpose KCa3.1, a calcium-activated potassium channel, regulates ion and fluid secretion in the lung and gastrointestinal tract. It is also expressed on vascular endothelium where it participates in blood pressure regulation. However, the expression and physiological role of KCa3.1 in blood-brain barrier (BBB) endothelium has not been investigated. BBB endothelial cells transport Na+ and Cl− from the blood into the brain transcellularly through the cooperation of multiple co-transporters, exchangers, pumps and channels. In the early stages of cerebral ischemia, when the BBB is intact, edema formation occurs by processes involving increased BBB transcellular Na+ transport. This study evaluated whether KCa3.1 is expressed on and participates in BBB ion transport. Methods The expression of KCa3.1 on cultured cerebral microvascular endothelial cells (CMEC), isolated microvessels and brain sections was evaluated by Western blot and immunohistochemistry. Activity of KCa3.1 on CMEC was examined by K+ flux assays and patch-clamp. Magnetic resonance spectroscopy and imaging were used to measure brain Na+ uptake and edema formation in rats with focal ischemic stroke following TRAM-34 treatment. Results KCa3.1 current and channel protein were identified on bovine CMEC and freshly isolated rat microvessels. In situ KCa3.1 expression on BBB endothelium was confirmed in rat and human brain sections. TRAM-34 treatment significantly reduced Na+ uptake, and cytotoxic edema in the ischemic brain. Conclusions BBB endothelial cells exhibit KCa3.1 protein and activity and pharmacological blockade of KCa3.1 appears to provide an effective therapeutic approach for reducing cerebral edema formation in the first 3 hours of ischemic stroke.

The potassium channel KCa3.1 constitutes a pharmacological target for neuroinflammation associated with ischemia/reperfusion stroke

“…In addition to activated microglia and macrophages, KCa3.1 is also expressed on blood-brain barrier endothelial cells, where it helps drive transcellular Na þ transport by the Na-K-Cl cotransporter (NKCC) and the Na/H exchanger (NHE) in the first few hours after ischemic stroke when the blood-brain barrier is still intact. 33 Using magnetic resonance spectroscopy and Na þ imaging, we recently demonstrated that TRAM-34 treatment started immediately before induction of permanent MCAO in rats significantly delayed edema formation and brain Na þ uptake. 33 These edema reducing effects of KCa3.1 inhibition are very likely responsible for the better outcomes of the KCa3.1 mice early after MCAO.…”

“…33 Using magnetic resonance spectroscopy and Na þ imaging, we recently demonstrated that TRAM-34 treatment started immediately before induction of permanent MCAO in rats significantly delayed edema formation and brain Na þ uptake. 33 These edema reducing effects of KCa3.1 inhibition are very likely responsible for the better outcomes of the KCa3.1 mice early after MCAO. It could of course also be argued that TRAM-34 was not optimally dosed in this study.…”

Fluid and ion transfer across the blood–brain and blood–cerebrospinal fluid barriers; a comparative account of mechanisms and roles

“…There are no reports of K + , Cl − cotransporters being present or active at the blood–brain barrier but also no reports of a careful search. By contrast many K + channels have been characterized in cultured brain microvascular endothelial cells using patch clamp experiments [240, 332, 338–348]. In acutely dissociated rat brain endothelial cells mRNA is present and there are functional signatures for channels containing Kv1.3, Kir2.1 and Kir2.2 [332].…”

Early Non-invasive Detection of Acute 1,2-Dichloroethaneinduced Toxic Encephalopathy in Rats

“…A disturbance of energy metabolism can contribute to the reduction of the ADC via cell swelling (23). Cerebral edemas likely formed in the presence of an intact blood-brain barrier (BBB) while transendothelial secretion of Na + , Cl − and water into the brain was greatly increased (24).…”