Identification of functional voltage-gated Na+ channels in cultured human pulmonary artery smooth muscle cells

Abstract

Electrical excitability, which plays an important role in excitation-contraction coupling in the pulmonary vasculature, is regulated by transmembrane ion flux in pulmonary artery smooth muscle cells (PASMC). This study aimed to characterize the electrophysiological properties and molecular identities of voltage-gated Na + channels in cultured human PASMC. We recorded tetrodotoxinsensitive and rapidly inactivating Na + currents with properties similar to those described in cardiac myocytes. Using RT-PCR, we detected transcripts of seven Na + channel α genes (SCN2A, 3A, 4A, 7A, 8A, 9A, and 11A), and two β subunit genes (SCN1B and 2B). Our results demonstrate that human PASMC express TTX-sensitive voltage-gated Na + channels. Their physiological functions remain unresolved, although our data suggest that Na + channel activity does not directly influence membrane potential, intracellular Ca 2+ release, or proliferation in normal human PASMC. Whether their expression and/or activity are heightened in the pathological state is discussed.Keywords membrane potential; Na + channels; vascular smooth muscle; pulmonary Voltage-gated Na + channels play a major role in regulating cell excitability, particularly as it pertains to the generation of action potentials in neurons, skeletal muscle, and cardiac myocytes. Evidence has shown that, in vascular smooth muscle, action potentials are not dependent on Na + channels since tetrodotoxin (TTX) has no effect on amplitude and duration of action potentials [18], leading to the belief that these channels might not be present or prominent in these tissues. Nonetheless, Na + currents (I Na ) have been measured in visceral smooth muscles such as myometrium and uterus (pregnant), colon, esophagus, stomach, and ureter as well as in certain vascular smooth muscles such as the portal and azygos veins [2,8,[24][25][26]31,33,34]. The identification of functional voltage-gated Na + channels in quiescent and proliferating vascular smooth muscle cells (VSMC), however, has not been as forthcoming. Currently, I Na have been measured in smooth muscle cells isolated from the coronary artery, aorta, vena cava, and pulmonary artery of various species, including humans [5,16,23,27]. On only rare occasions have I Na been recorded in freshly dissociated human VSMC, although they are readily detected when the same cells are cultured [28]. In isolated cases, I Na have been recorded in both freshly dispersed rabbit [27] de-differentiation and proliferation [28]. More specifically, voltage-gated Na + channel expression and activity may be required either to facilitate the transition or to promote the de-differentiation of cells from "contractile" to "synthetic" or "proliferative" phenotypes [20,30]. This raises the possibility that the expression of functional voltage-gated Na + channels in cultured cells act as a trigger for cell de-differentiation and proliferation, possibly via enhanced cytoplasmic free Ca 2+ concentration ([Ca 2+ ] cyt ).The molecular identification of the subunits that make ...

Ion channel switching and activation in smooth-muscle cells of occlusive vascular diseases

“…Others include voltage-gated Na + channel, T-type Ca 2+ channel, ClC-3 chloride channel, TRPC6 channel, inward rectifier K + channel, K V 3.4 channel and Na + -Ca 2+ exchange [20,[56][57][58][59][60][61][62][63]; conversely, loss of specific ion channels (e.g. K V 1.5) can also contribute [64].…”

Vinpocetine Suppresses Pathological Vascular Remodeling by Inhibiting Vascular Smooth Muscle Cell Proliferation and Migration

“…Moreover, vinpocetine is a potent voltage-gated sodium channel blocker (Bönöczk et al, 2000). The voltage-gated sodium channel has been found in several types of SMCs, and these channels seem to be important for SMC migration but not proliferation (Platoshyn et al, 2005;Meguro et al, 2009). Besides SMCs, the anti-inflammatory effects of vinpocetine on vascular cells and macrophages (Jeon et al, 2010b) may contribute to the inhibitory effects of vinpocetine in neointima formation.…”

The non-excitable smooth muscle: Calcium signaling and phenotypic switching during vascular disease

“…The physiological significance of increased Na + currents in proliferating cells remains a mystery. Platoshyn et al [109] showed evidence that increased Na + currents does not directly influence membrane potential, intracellular Ca 2+ release or proliferation in cultured human pulmonary artery smooth muscle. These authors speculated that increased Na + currents could contribute to activation of upregulated NCX in its reverse mode, leading to an increase of the bulk of cytoplasmic Ca 2+ and enhanced cell proliferation [109].…”