Functional expression of Na V 1.7 channels in freshly dispersed mouse bronchial smooth muscle cells.

Isolated smooth muscle cells (SMC) from mouse bronchus were studied using the whole-cell patch clamp technique at ~21o C. Stepping from -100 mV to -20 mV evoked inward currents of mean amplitude -275 pA. These inactivated (tau=1.1 ms) and were abolished when external Na+ was substituted with N-Methyl-D-glucamine. In current-voltage protocols, current peaked at -10 mV and reversed between +20 and +30 mV. The V1/2 sof activation and inactivation were -25 & -86 mV, respectively. The current was highly sensitive to tetrodotoxin (IC50 =1.5 nM) and the NaV 1.7 subtype selective blocker, PF-05089771 (IC50 =8.6 nM), consistent with NaV 1.7 as the underlying pore-forming a subunit. Two NaV 1.7-selective antibodies caused membrane-delineated staining of isolated SMC, as did a non-selective pan-NaV antibody. RT-PCR, performed on groups of ~15 isolated SMC, revealed transcripts for NaV 1.7 in 7/8 samples. Veratridine (30 mM), a non-selective NaV channel activator, reduced peak current evoked by depolarization but induced a sustained current of 40 pA. Both effects were reversed by tetrodotoxin (100 nM). In tension experiments veratridine (10 mM) induced contractions that were entirely blocked by atropine (1 mM). However, in the presence of atropine, veratridine was able to modulate the pattern of activity induced by a combination of U-46619 (a thromboxane A2 mimetic) & PGE2 (prostaglandin E2 ), by eliminating bursts in favour of sustained phasic contractions. These effects were readily reversed to control-like activity by tetrodotoxin (100 nM). In conclusion, mouse bronchial SMC functionally express NaV 1.7 channels that are capable of modulating contractile activity, at least under experimental conditions.