Molecular and biophysical properties of voltage-gated Na+ channels in murine vas deferens
Hai-Lei Zhu 1, Manami Aishima 1, Hidetaka Morinaga 1, Richard D Wassall 2, Atsushi Shibata 1, Kazuomi Iwasa 1, Masatoshi Nomura 1, Masaya Nagao 3, Katsuo Sueishi 1, Thomas C Cunnane 2 and Noriyoshi Teramoto 1*
1 Kyushu University
2 University of Oxford
3 Kyoto University
* To whom correspondence should be addressed. E-mail: noritera{at}med.kyushu-u.ac.jp.
Submitted on July 11, 2007
Revised on August 16, 2007
Accepted on 15 November 2007
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Abstract |
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The biological and molecular properties of tetrodotoxin (TTX)-sensitive voltage-gated Na+ currents (INa) in murine vas deferens myocytes were investigated using patch-clamp techniques and molecular biological analyses. In whole-cell configuration, a fast, transient inward current was evoked in the presence of Cd2+, and was abolished by TTX (Kd = 11.2 nM), mibefradil (Kd = 3.3 µM) and external replacement of Na+ with monovalent cations (TEA+, Tris+ and NMDG+). The fast transient inward current was enhanced by veratridine, an activator of voltage-gated Na+ channels, suggesting that the fast transient inward current was a TTX-sensitive INa. The values for half-maximal (Vhalf) inactivation and activation of INa were -46.3 mV and -26.0 mV respectively. RT-PCR analysis revealed the expression of Scn1a, 2a and 8a transcripts. The Scn8a transcript and the 
subunit protein of NaV1.6 were detected in smooth muscle layers. Using NaV1.6-null mice (NaV 1.6-/-) lacking the expression of the Na+ channel gene, Scn8a, INa were not detected in dispersed smooth muscle cells from the vas deferens, whilst TTX-sensitive INa were recorded in their wild-type (NaV1.6+/+) littermates. This study demonstrates that the molecular identity of the voltage-gated Na+ channels responsible the TTX-sensitive INa in murine vas deferens myocytes is primarily NaV1.6.
Key Words:
NaV1.6, Scn8a, Smooth muscle, TTX, Voltage-gated Na+ channels
