Pharmacological evidence for a key role of voltage‐gated K + channels in the function of rat aortic smooth muscle cells

The role of voltage‐dependent ( I Kv ) and large conductance Ca 2+ ‐activated (BK Ca ) K + currents in the function of the rat aorta was investigated using specific BK Ca and K V channel inhibitors in single rat aortic myocytes (RAMs) with patch‐clamp technique and in endothelium‐denuded aortic rings with isometric tension measurements. The whole‐cell K + currents were recorded in RAMs dialysed with 200 and 444 n M Ca 2+ and in perforated‐patch configuration. Electrophysiological analysis demonstrated that I Kv appeared at −40 mV, while BK Ca (isolated using 1 μ M paxilline) were seen positive to −20 mV in all conditions. Voltage‐dependent characteristics, but not maximal conductance, of I Kv was significantly altered in increased [Ca 2+ ] i . Correolide (1 μ M ) (a K V 1 channel blocker) did not inhibit the I Kv , whereas millimolar concentration of TEA (IC 50 =3.1±0.6 m M , n =5) and 4‐aminopyridine (4‐AP, IC 50 =5.9±1.9 m M , n =7) suppressed I Kv . These results and immunocytochemical analysis suggest the K V 2.1 channel to be a molecular correlate for I Kv . In nonstimulated aortic rings 1–5 m M TEA and 4‐AP (inhibitors of I Kv ), but not paxilline (1 μ M ), caused contraction. The frequency of contractile responses to TEA and 4‐AP was increased in the presence of 10 m M KCl, which itself did not significantly affect the aortic basal tone. Phenylephrine (15–40 n M ) induced sustained tension with superimposed slow oscillatory contractions (termed OWs). OWs were blocked by diltiazem, ryanodine and cyclopiazonic acid, suggesting the involvement of L‐type Ca 2+ channels and ryanodine‐sensitive Ca 2+ stores in this process. TEA and 4‐AP, but not IbTX, paxilline or correolide, increased the duration and amplitude of OWs, indicating that I Kv is involved in the control of oscillatory activity. In conclusion, our findings suggest that the K V 2.1‐mediated I Kv , and not BK Ca , plays an important role in the regulation of the excitability and contractility of rat aorta.British Journal of Pharmacology (2004) 143 , 303–317. doi: 10.1038/sj.bjp.0705957