Incomplete Inactivation of Voltage-dependent K+ Channels in Human B Lymphoma Cells

Abstract

The voltage-dependent K (KV) channel in Daudi human B lymphoma cells was characterized by using patch-clamp techniques. Whole-cell voltage-clamp experiments demonstrated that cell membrane depolarization induced a transient (time-dependent) outward current followed by a steady-state (time-independent) component. The time-dependent current resembled behavior of the type n channel, such as use dependence and a unique blockade by tetraethylammonium (TEA). Both time-dependent and time-independent currents were blocked by quinine with a similar IC50 (14.2 mM and 12.6 mM). Treatment with antisense oligonucleotide of human Kv1.3 gene significantly reduced both currents by 80%. Single-channel experiments showed that only one type of KV channel was recorded with a unitary conductance of approximately 19 pS. Consistent with whole-cell recordings, the channel activity in cell-attached patches remained in response to prolonged depolarization, and the remaining channel activity was blocked by quinine, but not TEA. Channel activity was scarcely seen in cell-attached patches after antisense treatment. Whole-cell current-clamp data showed that TEA, which blocks only the time-dependent current, caused a slight decrease in the membrane potential. In contrast, quinine and antisense, which block both time-dependent and -independent currents, strongly reduced the membrane potential. These data together suggest that the KV channel in Daudi cells does not completely inactivate and that the remaining channel activity due to this incomplete inactivation appears to be primarily responsible for maintaining the membrane potential.

Steroids and Exogenous γ-ENaC Subunit Modulate Cation Channels Formed by α-ENaC in Human B Lymphocytes

“…Consistent with our previous report (19), only outward K ϩ currents (but not any inward currents) were recorded as shown by a representative whole-cell recording from a total of 118 experiments (Fig. 1A).…”

An intermediate-conductance Ca2+-activated K+ channel mediates B lymphoma cell cycle progression induced by serum

“…Among K + channels, voltage-gated K + channel, as later referred to as Kv1.3 channel, was initially reported to affect proliferation of T lymphocyte [9]. We have previously shown that Kv1.3 channel is highly expressed in Daudi cells [41]. However, the present study suggests that an IK channel, instead of Kv1.3, is responsible for Daudi cell cycle progression.…”

“…Our previous finding that Kv1.3 channel is highly expressed in malignant Daudi B cells [41] prompted us to hypothesize that this voltage-dependent channel might mediate cell cycle progression of malignant B lymphocyte. Surprisingly, we found that Daudi cell cycle progression is not affected by selective inhibition of Kv1.3 channel with MgTX but inhibited by either nonselective blockage of K + channels with TEA or selective blockage of IK channels with TRAM-34.…”

“…The linear regression analysis of the I-V relationship between −80 and 80 mV (−V pipette ) yielded a unitary conductance of 30 pS. The reversal potential was approximately −40 mV, which is very close to the resting membrane potential of Daudi cells [41]. Four of these seven cell-attached patches were excised into a "cytoplasmic" bath solution in which free Ca 2+ was titrated to 50 nM and successfully formed inside-out patches.…”

“…Besides BK and SK channels, intermediate conductance K Ca (IK) channels also mediates proliferation of several cell types including activated T cells [18], endothelial cells [14], and cancer cells [17,30]. Although both voltage-gated Kv1.3 channels [28,35,41] and K Ca channels [11,32] are expressed in B lymphocytes, which one dominates proliferation of B lymphocytes, especially B lymphoma cells, remains undetermined. CD20, one of the most reliable markers of the B-cell lineage [6], has been suggested to serve as a calcium channel [5].…”