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(K(v))) 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 nm Ca(2+) and in perforated-patch configuration. Electrophysiological analysis demonstrated that I(K(v)) appeared at >/=-40 mV, while BK(Ca) (isolated using 1 microm paxilline) were seen positive to -20 mV in all conditions. Voltage-dependent characteristics, but not maximal conductance, of I(K(v)) was significantly altered in increased [Ca(2+)](i). Correolide (1 microm) (a K(V)1 channel blocker) did not inhibit the I(K(v)), whereas millimolar concentration of TEA (IC(50)=3.1+/-0.6 mm, n=5) and 4-aminopyridine (4-AP, IC(50)=5.9+/-1.9 mm, n=7) suppressed I(K(v)). These results and immunocytochemical analysis suggest the K(V)2.1 channel to be a molecular correlate for I(K(v)). In nonstimulated aortic rings 1-5 mm TEA and 4-AP (inhibitors of I(K(v))), but not paxilline (1 microm), 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 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(K(v)) is involved in the control of oscillatory activity. In conclusion, our findings suggest that the K(V)2.1-mediated I(K(v)), and not BK(Ca), plays an important role in the regulation of the excitability and contractility of rat aorta.
Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath, BA2 7AY.
Paolo
P
Tammaro
Amy L
AL
Smith
Simon R
SR
Hutchings
Sergey V
SV
Smirnov
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000473:pathology* / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D004594:Electrophysiology / Q000379:methods; D007120:Immunochemistry / Q000379:methods; D007211:Indoles / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010455:Peptides / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms; D051381:Rats; D017208:Rats, Wistar; D019789:Tetraethylammonium / Q000494:pharmacology; D014315:Triterpenes / Q000494:pharmacology; D006113:United Kingdom; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
D007211:Indoles; D010455:Peptides; D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated; D020033:Protein Isoforms; D014315:Triterpenes; C118657:correolide; C048220:paxilline; D019789:Tetraethylammonium; C064719:iberiotoxin