Na-dependent glutamate transport in high K and high glutathione (HK/HG) and high K and low glutathione (HK/LG) dog red blood cells

Abstract

Na-dependent glutamate (Glu) influxes in the red blood cells of normal low K (LK), high K and high glutathione (HK/HG), and high K and low glutathione (HK/LG) dogs were compared. The ranges of the influxes in LK, HK/HG and HK/LG cells were 1.0–63, 62–174 and 1.3–26 μmol/1 cells per h, respectively. Some LK and HK/LG dogs had red blood cells with extremely low Glu influxes. In cells with extremely low Glu influxes, however, there were clear Na-dependent Glu influxes. In LK, HK/HG and HK/LG cells, the K m of Na-dependent Glu influx with respect to the medium Glu concentration were 17, 20 and 19 mM, respectively, and the half-maximal activation ( K 1 2 ) with respect to medium Na concentration was 39, 40 and 42 μM, respectively. By the addition of harmaline, a hallucinogenic alkaloid, the V max in LK cells was not affected and the K m was increased, while the V max was decreased and the K m increased in HK/HG and HK/LG cells.The K i value with harmaline by means of Dixon plot in LK cells was 5.2 mM, against 1.8 and 1.9 mM in HK/HG and HK/LG cells, respectively. These results suggest that the difference in the Na-dependent Glu influxes between 2 HK groups was due to the varying quantity, not the quality, of the transporter.