Received February 23, 2008
Revised April 8, 2008
Accepted after revision April 8, 2008

¹ University of Massachusetts Medical School

^* To whom correspondence should be addressed. E-mail: mark.madison{at}umassmed.edu.

	Abstract

Large-conductance, calcium-activated potassium (BKCa) channels are regulated by voltage and near-membrane calcium concentrations and are determinants of membrane potential and excitability in airway smooth muscle cells. Because the T helper-2 (Th2) cytokine, interleukin (IL)-4, is an important mediator of airway inflammation, we asked if IL-4 rapidly regulated BKCa activity in normal airway smooth muscle cells. On-cell voltage clamp recordings were made on subconfluent, cultured human bronchial smooth muscle cells (HBSMC). IL-4 (50 ng/ml), IL-13 (50 ng/ml), or histamine (10 µM) was added to the bath during the recordings. Immunofluorescence studies with selective antibodies against the ? and ?1 subunits of BKCa were also performed. Both approaches demonstrated that HBSMC membranes contained large conductance channels (>200 pS) with both calcium and voltage sensitivity, all characteristic of the BKCa channel. Histamine caused a rapid increase in channel activity as expected. A new finding was that perfusion with IL-4 stimulated rapid, large increases in BKCa channel activity (77.2 ± 63.3-fold increase, p<0.05, n=18). This large potentiation depended on the presence of external calcium. In contrast, IL-13 (50 ng/ml) had little effect on BKCa channel activity, but inhibited the effect of IL-4. Thus, HBSMC contain functional BKCa channels whose activity is rapidly potentiated by the cytokine, IL-4, but not by IL-13. These findings are consistent with a model in which IL-4 rapidly increases near-membrane calcium concentrations to regulate BKCa activity.

Key Words: Airway, Interleukin, Potassium channel