The effects of hypo- and hyperkalemia on choroid plexus potassium transport.
To examine the mechanisms involved in cerebrospinal fluid (CSF) K+ homeostasis, lateral ventricle choroid plexuses were isolated from rats fed low, normal or high K+ diets for 2 weeks. Potassium (86Rb) influx and efflux were then examined in vitro. Dietary hypo- and hyperkalemia (2.8 +/- 0.1 and 6.8 +/- 0.3 mM) did not affect the efflux rate constant for 86Rb or the influx rate constant in the absence of inhibitors. However, the ouabain-sensitive portion of influx was only 1.9 +/- 0.5 microl/g per min in plexuses from hypokalemic rats compared to 4.5 +/- 0.5 microl/g/min in controls (P < 0.001). This change in Na+/K+-ATPase activity was reflected in an increasing amount (Western blot) of the alpha1 and beta1 subunits of this pump with increasing plasma K+ concentration (P < 0.05) whereas the beta2 subunit was unaffected. The other known choroid plexus K+ uptake mechanism, bumetanide-sensitive K+ cotransport, was unaffected by dietary K+ manipulation. In normo- and hyperkalemic rats, the sum of the ouabain- and bumetanide-sensitive fluxes could account for all of 86Rb uptake. However, in hypokalemic rats a major component (40%) of uptake could not be accounted for by either mechanism. This unidentified mechanism may be a basolateral uptake mechanism involved in increasing K+ transport from blood to CSF during hypokalemia.
Klarr
S A
SA
Department of Surgery (Neurosurgery), University of Michigan, Ann Arbor 48109-0532, USA.
Ulanski
L J
LJ
Stummer
W
W
Xiang
J
J
Betz
A L
AL
Keep
R F
RF
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002831:Choroid Plexus / Q000378:metabolism*; D006947:Hyperkalemia / Q000378:metabolism*; D007008:Hypokalemia / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D011188:Potassium