Table 1

Physiological Characteristics of Phagosomes from Nramp1 Wild-type (Nramp1+/+) and Nramp1/− Mice

Nramp1+/+Nramp1−/−
Buffering power* (mmol/pH/liter)    18 ± 2    16 ± 4
H+ consumption by ROI‡ (ΔpHp)0.2 ± 0.05 0.3 ± 0.1
Net H+ efflux§ (pH/min)0.2 ± 0.030.2 ± 0.02
Counterion conductance‖ (ΔpHp)0.3 ± 0.030.2 ± 0.04
  • *  Macrophages from wild-type and Nramp1−/− mice that had internalized live M. bovis were pulsed with small aliquots of NH4Cl (1–2 mM). The change in pHp resulting from entry and protonation of NH3 was used to compute the buffering power, which was compared in the 6.5– 6.8 range in both cell types.  

  •  Macrophages from both strains that had internalized live M. bovis were treated with the flavoprotein inhibitor diphenylene iodonium (3 μM), and steady state pHp was reached. Results are expressed as pHp after addition minus pHp before addition.  

  • §  Net phagosomal H+ efflux was induced in macrophages from wild-type and Nramp1−/− mice that had internalized live M. bovis by addition of concanamycin (100 nM). Because the buffering power of both types of phagosomes is similar, the fluxes are expressed as the rates of change of pH per unit time, and were made at comparable pHp.  

  •  Cells from both strains were allowed to internalize live M. bovis in a K+-rich medium. After steady state pHp was reached, cells were treated with valinomycin (10 μM), a conductive K+ ionophore. Results are expressed as pHp after addition minus pHp before addition.