TY - BOOK ID - 127141441 TI - Etude des propriétés électrophysiologiques et pharmacologiques des canaux potassiques voltage-dépendants dans les cellules musculaires lisses vasculaires AU - Baeyens, Nicolas AU - Morel, Nicole AU - UCL.. MD/FSIO/FYCL - Laboratoire de physiologie cellulaire PY - 2007 PB - Bruxelles: UCL, DB - UniCat KW - Potassium Channels, Voltage-Gated KW - Myocytes, Smooth Muscle KW - Muscle, Smooth, Vascular KW - Electrophysiology KW - Pharmacology UR - https://www.unicat.be/uniCat?func=search&query=sysid:127141441 AB - Potassium channels play a prominent role in the regulation of membrane potential. Among these channels, voltage-dependent Kv channels form a large family of proteins in which several subtypes have been identified (Kv1.x to Kv 11.x). These channels are involved in several pathologies and might contribute to the development of arterial hypertension.
The aim of this work is to study the pharmacological and electrophysiological properties of Kv channels expressed in mesenteric artery. We have used whole cell patch clamp technique on freshly isolated smooth muscle cells from the rat superior mesenteric artery.
We have recorded potassium currents activating around -40 mV and showing a slow inactivation (τ≈3s) in response to a prolonged depolarising stimulation (10s). Only the inactivating component of the current is sensitive to 4-aminopyridine, a selective inhibitor of Kv channels (0.1 to 5mM).
In order to investigate the potential modulation of these channels by calcium, we have tested the effect of 0 and 2 mM calcium in the extracellular solution. No alteration in the Kv current was associated with the change in extracellular calcium. Surprisingly, lowering the extracellular calcium concentration markedly decreased the inhibitory effect of the low concentrations of 4-aminopyridine (4-AP, 0.1 to 0.5 mM) on the K current : 0.5 mM 4-AP inhibited the inactivating component of the K current by 8% in the absence of calcium compared to 35% in the presence of 2 mM calcium. The effect of higher concentrations of 4-AP was unaffected. 4-AP inhibition was also tested in the presence of nimodipine, an inhibitor of L-type voltage-gated calcium channels, to determine whether intracellular calcium could affect the inhibitory potency of 4-AP. Our results show that K current inhibition by 4-AP was increased in the presence of nimodipine, suggesting that calcium entry also plays a role in the modulation of Kv channels.
The contribution of the different subtypes of Kv channels to the current was investigated to determine whether the effect of calcium on low 4-AP concentration was related to the nature of the Kv isoform involved in the response. A Western-Bolt study identified the expression of Kv2.1 in mesenteric artery form Wistar rat. This was confirmed by using stromatoxin, a reported specific inhibitor of Kv2.x channels. Stromatoxin inhibited more than 45% of the inactivating component of the K current, but did not affect either the fraction of the current sensitive to low 4-AP, or the calcium modulation of the effect of 4-AP. In the presence of stromatoxin, the typical U shape of the steady state inactivation curve, which is a property of Kv2.1 channel current, disappeared, and the inactivation curve wwas shifted to voltages. Psora-4, a new inhibitor of Kv1.3 and Kv1.5 was tested to study the involvement of these channels in the K current. Preliminary results indicated that psora-4 inhibited the inactivating component by 18% but strongly inhibited the non-inactivating component of the current. Psora-4 only partially inhibited the 0.5 mM 4-AP-sensitive K current.
Taken together, these results suggest that Kv1.5/Kv1.3 but not Kv2.1 contribute to the component of the K current sensitive to low concentration of 4-AP.
Functional role of the 4-AP stromatoxin-sensitive currents was tested by measuring the contractile activity evoked by increasing KCI concentrations from 6 to 15mM in the presence of the calcium channel agonist BayK8644 in isolated mesenteric artery mounted in a myograph. The results showed that in the presence of 4-AP 0.5 and 5 mM, contraction was increased for KCI. These data indicated that the K channels identified in the electrophysiology experiments play a role in the regulation of the membrane potential ER -