[H-3] HISTAMINE UPTAKE AND RELEASE BY ASTROCYTES FROM RAT-BRAIN - EFFECTS OF SODIUM DEPRIVATION, HIGH POTASSIUM, AND POTASSIUM CHANNEL BLOCKERS

Histamine transport has been characterized in cultured astroglial cells of rat brain. The kinetics of [H-3]-histamine uptake yielded a K-m of 0.19 +/- 0.03 mu M and a V-max of 3.12 +/- 0.75 pmol X mg protein(-1) X min(-1). Transport system revealed high affinity for histamine and an approximately ten times higher capacity than that shown in cultured glial cells of chick embryonic brain. Ouabain which interferes with utilization of ATP to generate ion gradients, and the replacement of Na+ with choline inhibited the initial rate of uptake showing a strong Na+-dependency and suggesting the presence of a tightly coupled sodium/histamine symporter. Dissipation of K+-gradient (in > out) by high K+ or by K+-channee blockers, BaCl2, (100 mu M), quinine (100 mu M) or Sparteine (20 mu M) produced also remarkable inhibitions in the uptake of [H-3]-histamine. Impromidine, a structural histamine-analogue could inhibit the uptake non-competitively in a range of concentrations of 1 to 10 mu M with a K-i value of 2.8 mu M, indicating the specificity of the uptake. [H-3]histamine uptake measurements carried out by using a suspension of dissociated hypothalamic cells, of rat brain showed a strong gliotoxin-sensitivity and yielded a Km of 0.33 +/- 0.08 mu M; and a V-max of 2.65 +/- 0.35 pmoles X mg protein(-1) X min(-1). The uptake could be reversed by incubating the cells in histamine-free Krebs medium. The [H-3]histamine efflux was sensitive to Na+ omission, ouabain treatment and high K+ or K+ channel blockers, resulting in marked elevations in the efflux. Data indicate that glial uptake of histamine is a high affinity, Na+-dependent and electrogenic, driven by an inward-oriented sodium ion gradient and an outward-oriented potassium ion gradient and functions as part of histamine inactivation, at least in a shunt mechanism.