Expression and function of the Scn5a-encoded voltage-gated sodium channel NaV1.5 in the rat jejunum

BackgroundThe SCN5A-encoded voltage-gated sodium channel Na(V)1.5 is expressed in human jejunum and colon. Mutations in Na(V)1.5 are associated with gastrointestinal motility disorders. The rat gastrointestinal tract expresses voltage-gated sodium channels, but their molecular identity and role in rat gastrointestinal electrophysiology are unknown. MethodsThe presence and distribution of Scn5a-encoded Na(V)1.5 was examined by PCR, Western blotting and immunohistochemistry in rat jejunum. Freshly dissociated smooth muscle cells were examined by whole cell electrophysiology. Zinc finger nuclease was used to target Scn5a in rats. Lentiviral-mediated transduction with shRNA was used to target Scn5a in rat jejunum smooth muscle organotypic cultures. Organotypic cultures were examined by sharp electrode electrophysiology and RT-PCR. Key ResultsWe found Na(V)1.5 in rat jejunum and colon smooth muscle by Western blot. Immunohistochemistry using two other antibodies of different portions of Na(V)1.5 revealed the presence of the ion channel in rat jejunum. Whole cell voltage-clamp in dissociated smooth muscle cells from rat jejunum showed fast activating and inactivating voltage-dependent inward current that was eliminated by Na+ replacement by NMDG(+). Constitutive rat Scn5a knockout resulted in death in utero. Na(V)1.5 shRNA delivered by lentivirus into rat jejunum smooth muscle organotypic culture resulted in 57% loss of Scn5a mRNA and several significant changes in slow waves, namely 40% decrease in peak amplitude, 30% decrease in half-width, and 7 mV hyperpolarization of the membrane potential at peak amplitude. Conclusions & InferencesScn5a-encoded Na(V)1.5 is expressed in rat gastrointestinal smooth muscle and it contributes to smooth muscle electrophysiology.