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

• Published in: British journal of pharmacology 2004-09, Vol.143 (2), p.303-317
• Main Authors: Tammaro, Paolo, Smith, Amy L, Hutchings, Simon R, Smirnov, Sergey V
• Format: Article
• Language: English
• Subjects: Animals; Aorta, Thoracic - drug effects; Aorta, Thoracic - pathology; Aorta, Thoracic - physiology; Biological and medical sciences; Ca2+‐activated K+ channels; Calcium Signaling - drug effects; Calcium Signaling - physiology; Electrophysiology - methods; Immunochemistry - methods; Indoles - pharmacology; KV2.1 channel; Male; Medical sciences; Membrane Potentials - drug effects; Muscle, Smooth, Vascular - cytology; Muscle, Smooth, Vascular - drug effects; Muscle, Smooth, Vascular - physiology; Myocytes, Smooth Muscle - drug effects; Myocytes, Smooth Muscle - physiology; Patch-Clamp Techniques - methods; patch‐clamp technique; Peptides - pharmacology; Pharmacology. Drug treatments; potassium channels; Potassium Channels, Calcium-Activated - drug effects; Potassium Channels, Calcium-Activated - physiology; Potassium Channels, Voltage-Gated - drug effects; Potassium Channels, Voltage-Gated - genetics; Potassium Channels, Voltage-Gated - metabolism; Protein Isoforms; rat; Rats; Rats, Wistar; rhythmic contraction; single smooth muscle cells; Tetraethylammonium - pharmacology; thoracic aorta; Triterpenes - pharmacology; United Kingdom; Vascular smooth muscle cells; Vasoconstriction - drug effects; Vasoconstriction - physiology; voltage‐gated K+ channels
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0705957

The role of voltage‐dependent (IKv) and large conductance Ca2+‐activated (BKCa) K+ currents in the function of the rat aorta was investigated using specific BKCa and KV 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 nM Ca2+ and in perforated‐patch configuration. Electrophysiological analysis demonstrated that IKv appeared at −40 mV, while BKCa (isolated using 1 μM paxilline) were seen positive to −20 mV in all conditions. Voltage‐dependent characteristics, but not maximal conductance, of IKv was significantly altered in increased [Ca2+]i. Correolide (1 μM) (a KV1 channel blocker) did not inhibit the IKv, whereas millimolar concentration of TEA (IC50=3.1±0.6 mM, n=5) and 4‐aminopyridine (4‐AP, IC50=5.9±1.9 mM, n=7) suppressed IKv. These results and immunocytochemical analysis suggest the KV2.1 channel to be a molecular correlate for IKv. In nonstimulated aortic rings 1–5 mM TEA and 4‐AP (inhibitors of IKv), but not paxilline (1 μM), caused contraction. The frequency of contractile responses to TEA and 4‐AP was increased in the presence of 10 mM KCl, which itself did not significantly affect the aortic basal tone. Phenylephrine (15–40 nM) 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 Ca2+ channels and ryanodine‐sensitive Ca2+ stores in this process. TEA and 4‐AP, but not IbTX, paxilline or correolide, increased the duration and amplitude of OWs, indicating that IKv is involved in the control of oscillatory activity. In conclusion, our findings suggest that the KV2.1‐mediated IKv, and not BKCa, 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