No abstract

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.