Trypanosoma lewisi: Alterations in membrane function in the rat

Abstract

DEAE-cellulose-purified Trypanosoma lewisi from 4-day (dividing trypanosomes) and 7-day (non-dividing trypanosomes) infections in rats were compared for initial uptake of glucose, leucine, and potassium. Glucose entered the parasitic cells by mediated (saturable) processes, whereas leucine and K + entered by mediated processes and diffusion. Glucose entry was significantly elevated in 4-day cells ( V max 4.00 ± 1.02 nmoles/ 1 × 10 8 cells/min) with respect to 7-day cells ( V max 1.83 ± 0.62 nmoles 1 × 10 8 cells/min). Likewise, the affinity of the glucose carrier was significantly greater in 4-day cells ( K m = 0.30 ± 0.02 m M) than in 7-day cells ( K m = 0.59 ± 0.11 m M). When leucine and K + transport were compared in 4- and 7-day populations, significant elevations in the rate of entry ( V max) of both substrates were observed for 4-day cells; K m values for leucine and K + were not altered by the stage of infection. For leucine, the V max and K m for 4-day cells were 2.40 ± 0.50 nmoles/1 × 10 8 cells/30 sec and 78 ± 7 μ M, respectively; corresponding values in 7-day cells were 1.06 ± 0.02 nmoles/1 × 10 8 cells/30 sec and 66 ± 11 μ M. For K +, the V max and K m for 4-day cells were 15.97 ± 0.38 nmoles/1 × 10 8 cells/min and 1.2 m M, respectively; corresponding values in 7-day cells were 4.76 ± 1.82 nmoles/1 × 10 8 cells/min and 1.05 m M. The observed increase in the rate of K + entry into 4-day cells was attributable to enhanced influx; no significant difference in the rate of K + efflux was noted when 4- and 7-day cells were compared ( t 1 2 of K + leak for 4- and 7-day cells were 68.1 ± 9.3 and 67.9 ± 15.2 min, respectively). Potassium influx was ouabain insensitive. Membrane function in 7-day cells was not uniformly inhibited. No significant difference in the activity of the membrane-bound enzyme, 5′-nucleotidase, was observed when 4- and 7-day cells were compared.