Stability of the potassium content of cerebrospinal fluid and brain

Proceedings of the Physiological Society, 11‐12 November 1983, Queen Elizabeth College, London Meeting: Communications

“…This value is comparable to Lp values reported for red cell membranes (Terwilliger & Solomon, 1981) but not to the value reported for baso-lateral membranes of rabbit proximal tubule (Welling, Welling & Ochs, 1983 The potassium content of the brain is normally maintained constant despite wide fluctuations in plasma K+ (Bradbury & Kleeman, 1967); resting blood-to-brain 42K flux in the rat is 2-3 pumol g-1 h-1 (Katzman & Leiderman, 1953). Orkand, Nicholls & Kuffler (1966) proposed that the glia contribute substantially to homeostasis of extracellular K+ (Ke) by 'spatial buffering'.…”

Graphical Evaluation of Blood-to-Brain Transfer Constants from Multiple-Time Uptake Data

“…As presented in the introduction, Bradbury and Kleeman (1967) first conceived of the multiple time/graphical approach and applied it to their studies of tracer potassium exchange between blood and brain. In this study and the similar ones by Bradbury and co-workers (Wong and Bradbury, 1975;Sarna et aI., 1977) and by Banos and col-6 c. S. PATLAK ET AL.…”

“…A number of studies have indicated that the rapid distribution spaces of extracellular solutes in the blood -brain system may be something more than the plasma space. For instance, Sisson and Olden dorf (1971), using the approach of Bradbury and Kleeman (1967), found the following relationship between the rapidly exchanging spaces of four sol utes: plasma globulin (probably transferrin) = 14C_ dextran (molecular weight, 60,000-90,000) < 14C_ inulin (nominal molecular weight, 5,000-5,500) < 3H-mannitol (molecular weight, 182). Further dis cussion of this space for both extracellularly and intracellularly distributing solutes is given in the following paper (Blasberg et aI., 1983).…”

“…As will be presented in this paper, the injection of the test material by intrave nous bolus is certainly an acceptable experimental and theoretical alternative to the more complex in fusion schedules required for the constant blood level conditions used by Bradbury and Kleeman (1967) and by Banos et al (1973). However, the employment of a single experimental period to de termine the influx constant can lead to erroneous estimates if there is a significant brain-to-blood backflux during the experimental period and/or the measured tissue activity of the test solute is not corrected for the activity that has not moved com pletely across the BBB at the time of tissue sam pling.…”

“…In addition, this assumption confines the estimation of the influx constant to experimental situations in which the uni directional character of tissue uptake can be dem onstrated. Bradbury and Kleeman (1967) recognized that brain cells serve as a sink for potassium that has moved across brain capillaries and into brain ex tracellular fluid, and that this cellular sink would probably lead to a purely unidirectional transfer of tracer potassium across the BBB for several hours after intravenous administration. Therefore, these authors assumed a unidirectional uptake model for the blood-to-brain transfer of tracer potassium, es tablished relatively constant blood levels of 42K in their experimental animals, obtained brain samples at times ranging from 30 min to 3 h, and graphed the data from all of the experiments as the tissue/plasma concentration ratio of radioactivity versus the ex perimental duration.…”