No correlation between membrane potential and increased cytosolic free Ca2+ concentration, 86Rb+ influx or subsequent [3H]-thymidine incorporation in neoplastic human B cells stimulated with antibodies to surface immunoglobulin.

We have followed the changes in the membrane potential of neoplastic B cells after addition of antibodies to cell specific surface immunoglobulin heavy chains (anti-Ig). Two methods were used, both based on the distribution of lipophilic fluorescent indicators: the anionic bis(1,3-diethylthiobarbiturate)-trimethine oxonol (fluorescence measurement made on whole cell suspensions) and the cationic 3,3-dihexyloxacarbocyanine iodide (diOC6-(3] (using flow cytofluorimetric analysis). By the latter method, the resting membrane potential was calculated to range from -40 to -63 mV. The stimulatory effect of anti-Ig was investigated on two B cell populations. In one, which may be stimulated in this way to [3H]-thymidine incorporation, the membrane potential was apparently unchanged, at least during the first hour of stimulation. In the other population, anti-Ig induced a rapid depolarization (oxonol method), but these cells did not, on the other hand, respond with [3H]-thymidine incorporation. The nature of this depolarization was further investigated. Both Na+ and K+ permeabilities appeared increased, while Ca2+ influx did not contribute to the change in membrane potential. Nor did depolarization itself change free cytosolic Ca+ concentration, [Ca2+]i, as estimated by the quin-2 method. Furthermore, anti-Ig stimulation increased [Ca2+]i in these cells, even when depolarization was abolished by lowering the extracellular Na+ concentration. Thus, in cells where depolarization could be demonstrated, it was linked neither to early changes in [Ca2+]i nor to late [3H]-thymidine incorporation. In contrast, such effects of anti-Ig stimulation were observed in other cells without any significant early change in the membrane potential.