The intermediate-conductance Ca(2+)-activated K(+) channel KCa3.1/KCNN4 plays an important role in the modulation of Ca(2+) signaling through the control of the membrane potential in T lymphocytes. Here, we study the involvement of KCa3.1 in the enlargement of the mesenteric lymph nodes (MLNs) in a mouse model of inflammatory bowel disease (IBD). The mouse model of IBD was prepared by exposing male C57BL/6J mice to 5% dextran sulfate sodium for 7 days. Inflammation-induced changes in KCa3.1 activity and the expressions of KCa3.1 and its regulators in MLN CD4(+) T lymphocytes were monitored by real-time PCR, Western blot, voltage-sensitive dye imaging, patch-clamp, and flow cytometric analyses. Concomitant with an upregulation of KCa3.1a and nucleoside diphosphate kinase B (NDPK-B), a positive KCa3.1 regulator, an increase in KCa3.1 activity was observed in MLN CD4(+) T lymphocytes in the IBD model. Pharmacological blockade of KCa3.1 elicited the following results: 1) a significant decrease in IBD disease severity, as assessed by diarrhea, visible fecal blood, inflammation, and crypt damage of the colon and MLN enlargement compared with control mice, and 2) the restoration of the expression levels of KCa3.1a, NDPK-B, and Th1 cytokines in IBD model MLN CD4(+) T lymphocytes. These findings suggest that the increase in KCa3.1 activity induced by the upregulation of KCa3.1a and NDPK-B may be involved in the pathogenesis of IBD by mediating the enhancement of the proliferative response in MLN CD4(+) T lymphocyte and, therefore, that the pharmacological blockade of KCa3.1 may decrease the risk of IBD.

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The renin-angiotensin system (RAS) is a critical regulator of sodium balance, extracellular fluid volume, vascular resistance, and, ultimately, arterial blood pressure. The key RAS molecule angiotensin II type 1 receptor (AT1R), and another major determinant of vascular tone, the large conductance calciumactivated potassium (BK Ca ) channel, are both highly expressed in renal arterial smooth muscle cells (SMCs). Our previous studies in expression systems revealed a physical association between AT1R and BK Ca , and that AT1R association modified BK Ca channel voltage sensitivity. However, the effect of Ang II on BK Ca channels in renal arterial SMCs needs to be defined. Furthermore, whether AT1R association is critical for the alteration of channel activity in response to Ang II, and whether the coupling changes BK Ca reactivity to specific inhibitors also remain unknown. Our present studies in rat renal arterial SMCs show that application of 100 nM Iberiotoxin (IbTx, a specific BK Ca channel blocker) inhibits whole-cell BK Ca currents by 63.0512.5% (n=5). IbTxsensitive BK Ca currents were reduced by 44.458.7% (n=3) in response to 1 mM Ang II treatment. In AT1R-IRES-BK Ca -transfected HEK293T cells, extracellular application of 1 mM Ang II also suppressed whole-cell BK Ca currents by 19.750.3% (n=3), while this treatment made no significant changes in cells expressing only BK Ca (n=6). IbTx reduced the whole-cell currents by 37.251.9% (n=4) in BK Ca -transfected HEK293T cells and 37.7512.5% (n=5) in AT1R-IRES-BK Ca -transfected cells. Paxilline treatment (100 nM) produced a 66.858.0% (n=3) reduction of BK Ca whole-cell currents in BK Ca -transfected HEK293T cells and 65.859.2% (n=3) reduction in AT1R-IRES-BK Ca -transfected cells. These results demonstrate that Ang II inhibits BK Ca channel activity in renal arterial SMCs and suggest that AT1R serves as the mediator of the effect. However, the interaction between AT1R and BK Ca does not change channel reactivity towards specific channel inhibitors. Supported by NIH.