Differential Functional Expression of Clotrimazole-sensitive -activated Current in Bal-17 and WEHI-231 Murine B Lymphocytes

The intermediate conductance $Ca^{2+}-activated$ $K^+$ channels (SK4, IKCa1) are present in lymphocytes, and their membrane expression is upregulated by various immunological stimuli. In this study, the activity of SK4 was compared between Bal-17 and WEHI-231 cell lines which represent mature and immature stages of murine B lymphocytes, respectively. The whole-cell patch clamp with high-$Ca^{2+}$ ($0.8{\mu}M$) KCl pipette solution revealed a voltage-independent $K^+$ current that was blocked by clotrimazole (1 mM), an SK4 blocker. The expression of mRNAs for SK4 was confirmed in both Bal-17 and WEHI-231 cells. The density of clotrimazole-sensitive SK4 current was significantly larger in Bal-17 than WEHI-231 cells ($-11.4{\pm}3.1$ Vs. $-5.7{\pm}1.15$ pA/pF). Also, the chronic stimulation of B cell receptors (BCR) by BCR-ligation (anti-IgM Ab, $3{\mu}g$/ml, 8∼12 h) significantly upregulated the amplitude of clotrimazolesensitive current from $-11.4{\pm}3.1$ to $-53.1{\pm}8.6$ pA/pF in Bal-17 cells. In WEHI-231 cells, the effect of BCR-ligation was significantly small ($-5.7{\pm}1.15$ to $-9.0{\pm}1.00$ pA/pF). The differential expression and regulation by BCR-ligation might reflect functional changes in the maturation of B lymphocytes.