Potassium fluxes across the blood brain barrier of the cockroach, Periplaneta americana

Potassium fluxes across the blood–brain barrier of the cockroach Periplaneta americana were measured using the scanning ion-selective microelectrode technique. In salines containing 15 mM or 25 mM K+, an efflux of K+ from the ganglia of isolated nerve cords was counterbalanced by an influx across the connectives. Metabolic inhibition with CN− resulted in an increase in K+ efflux across both the ganglia and the connectives. Depletion of K+ by chilling the nerve cords in K+-free saline was associated with subsequent K+ influx across the connectives in K+-replete saline at room temperature. There were dramatic increases in K+ efflux across both ganglia and connectives when the nerve cords were exposed to the pore-forming antibiotic amphotericin B. K+ fluxes across the ventral nerve cord were also altered when paracellular leakage was augmented by transient exposure to 3 M urea. K+ efflux was reduced by the K+ channel blockers Ba2+ and tetraethylammonium or by exposure to Ca2+-free saline and K+ efflux from the ganglia was increased by addition of ouabain to the bathing saline. The results provide direct support for a model proposing that K+ is cycled through a current loop between the ganglia and the connectives and that both the Na+/K+-ATPase and K+ channels are implicated in extracellular K+ homeostasis within the central nervous system.