Recombinant murine interferon-gamma-induced differentiation of pre-B lymphocytes is associated with Na+/H+ exchange-dependent and -independent cytoplasmic alkalinization.

Abstract

We have previously shown that in a murine pre-B lymphocyte cell line, 70Z/3, interleukin-1-induced IgM expression (differentiation) was associated with Na+/H+-mediated cytoplasmic alkalinization. Because interferon-gamma also induces 70Z/3 differentiation, in this study we examined the effects of recombinant murine interferon-gamma (rIFN-gamma) on cell pH. We found that rIFN-gamma (50 units/ml) induced a sustained increase in cell pH, averaging 0.09 pH units above the base line at 30 min and 0.08 at 4 h. Because rIFN-gamma also induced increases in cell Na+ concentration, the data suggests stimulation of Na+/H+ exchange across the cell membrane. Amiloride inhibited the rIFN-gamma-mediated pH rise by only 31% at 30 min, but at 4 h the inhibition was more complete (89%). In contrast to pHi, amiloride totally blocked the Na+ rise at both 30 min and 4 h. This indicates that at the earlier time point the pH rise had a Na+/H+ exchange-dependent and -independent component while at the later time most of the pH rise was due to the Na+/H+ exchanger. The presence of a Na+ independent amiloride-insensitive component was further confirmed by the 0.05 pH rise induced by rIFN-gamma in Na+-free media. Failure to block the Na+-independent rIFN-gamma-mediated pHi rise by anion exchange inhibitors or removal of Ca2+ indicate that this component was not mediated by Cl-/OH- or Ca2+/H+ exchange. The nature of the Na+-independent cell alkalinization process or its role in rIFN-gamma-mediated 70Z/3 differentiation remains to be determined. Because amiloride did not have an effect on rIFN-gamma-induced surface Ig expression or the rIFN-gamma-mediated increase in new kappa light chain-specific mRNA the results indicate that rIFN-gamma-stimulated Na+/H+ is not required for 70Z/3 differentiation.