Ion channel blockers inhibit B cell activation at a precise stage of the G1 phase of the cell cycle. Possible involvement of K+ channels.

Lymphocytes express voltage-activated K+ channels in their membrane. Combining the patch-clamp techniques of recording with immunological methods, we have analyzed the expression and the involvement of these channels during defined steps of LPS-induced B cell activation. We show that the number of K+ channels increased strongly when B cells entered in the G1 phase of the cell cycle. The involvement of ion channels in B cell proliferation was assessed using channel blockers that inhibit the K+ current. It was first found that TEA, but not TMA, quinine and verapamil totally suppressed both K+ current and DNA synthesis by stimulated lymphocytes as measured by [3H]TdR uptake or propiedium iodide staining. The drugs affected neither the induction by LPS of activation markers such as Ag of the murine class II MHC and type II receptor for the Fc region of IgG nor the initial cell enlargement that occur early during activation. These data indicate that functional K+ channels are not essential for the transition from the G0 to the G1 phases. In contrast, the same channel antagonists blocked the induction of transferrin receptor expression, characteristic of the final stages of G1. These drugs acted on cells already in G1, because their addition 30 h after LPS still suppressed DNA synthesis, and because they inhibited the proliferation of purified B cell blasts. The effect of tetraethylammonium was reversible, a lag period of 12 h occurring before the cells start DNA synthesis after drug removal. Taken together, these data demonstrate that the proliferation of LPS-stimulated B cells requires functional ion channels at a critical period in the G1 phase, taking place before transferrin receptor expression and the entry into the S phase. The involvement of voltage dependent K+ channels at this particular point is suggested by the parallel effects of the drugs used on K+ currents and DNA synthesis.