The mechanism of the exclusion of sodium ions and the concentration of potassium ions by guinea-pig cerebral cortex slices.

Abstract

Abstract—Guinea pig cerebral slices were incubated in oxygenated Krebs‐Ringer bicarbonate glucose saline for periods of 1 s to 60 min, and their swelling and Na+ and K+ cone were measured. The swelling was at the rate of 8 per cent for the 1st min, and 0·8 per cent for the next 29 min; it fell significantly during the subsequent 30 min (P= 0·05). The Na+ and K+ concn in the tissue fluctuated during the 1st min of incubation, but the Na+ concn had risen to a mean of 108 mm after 1 min incubation and the K+ concn had fallen to a mean of 52 mm by 3 min. The concentrations of these cations did not change significantly after these times. Cerebral slices were also incubated for 30 min in isotonic media modified such that Na+, + K+, Na++ choline+, or K++ choline+ always added up to 150 mm. It was found that about half of the swelling (20‐25 per cent) was independent of the Na+ or K+ concn and a further 20‐25 per cent of the swelling varied with the cations only if Na+ and K+ were both present and was a function of the K+ concn in the medium (0·15 per cent m‐mol). The Na+ concn in the tissue was a mean 8·4 mm after incubation in a Na+‐free medium and 7·1 mm in K+ after incubation in a K+‐free medium. Cerebral slices in the presence of Na++ K+ excluded one molecule of Na+ for every four molecules in the incubating medium; they accumulated K+ from the medium until the concn in the medium exceeded 130 mm.