Plasticity of TRPC expression in arterial smooth muscle: correlation with store-operated Ca²⁺ entry

Abstract

. Contractility of rat cerebral arteries in organ culture is preserved for several days, whereas SOCE is increased. In correlation with this increase is that nifedipine-insensitive whole cell current, activated by depletion of intracellular Ca 2ϩ stores, was increased by 50% in cells isolated from arteries cultured for 3 days. TRPC1 and TRPC6 mRNA were more than fivefold increased in cells isolated after organ culture, whereas TRPC3 was decreased. Immunofluorescent staining and/or Western blotting of arteries and isolated cells showed upregulation of TRPC1 and TRPC6 proteins during organ culture. In intact arteries, TRPC4 expression correlated with the amount of endothelium present. Ca 2ϩ addition after store depletion caused a contraction in cultured, but not in freshly dissected, arteries. A polyclonal TRPC1 antibody directed against an extracellular epitope inhibited this contraction by ϳ50%. To investigate the basis of the TRPC upregulation and assess its possible clinical significance, segments of human internal mammary artery were organ cultured for 24 h and then exposed to balloon dilatation in vitro, followed by further culturing for up to 48 h. After dilatation, TRPC1 and TRPC6 mRNA were progressively increased compared with undilated control segments. The results of this study indicate that vascular injury enhances plasticity in TRPC expression, that TRPC expression correlates with cellular Ca 2ϩ handling, and that TRPC1 is a subunit of upregulated store-operated Ca 2ϩ channels.

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

“…In VSMC in culture and in models of VSMC injury as well as in other cases of vascular disease, TRPC channel expression dramatically increases. Specifically, the loss in contractile phenotype in proliferative VSMC in culture correlated with over fivefold increase in TRPC1 and TRPC6 mRNA and protein expression and increased whole cell Ca 2+ currents [14]. In the same study, balloon dilatation of human internal mammary artery showed a similar increase in TRPC1 and TRPC6 mRNA expression 48 h post injury [14].…”

“…Specifically, the loss in contractile phenotype in proliferative VSMC in culture correlated with over fivefold increase in TRPC1 and TRPC6 mRNA and protein expression and increased whole cell Ca 2+ currents [14]. In the same study, balloon dilatation of human internal mammary artery showed a similar increase in TRPC1 and TRPC6 mRNA expression 48 h post injury [14]. TRPC1 is upregulated following experimental vascular injury in mice and pigs, and is associated with the conversion of smooth muscle cells from a quiescent to a proliferative phenotype initiating neointimal formation [74].…”

“…Most studies of VSMC phenotypic switching have focused on identification of factors that promote this process (e.g., growths factors and cytokines, oxidative stress, mechanical stress, endothelial factors) or on transcriptional regulation of phenotype-specific genes [70,101,102]. These studies have mainly focused on the loss of contractile proteins with very few reports devoted to the acquisition of proproliferative or pro-migratory proteins such as ion channels and pumps [14,32,74].…”

“…Most of the regulatory aspects of VSMC contractile genes identified to date have been shown to depend on CArG regulatory sequences found in their promoters and on the binding of the transcription factor serum response factor (SRF) [102,147]. In recent years, increasing number of studies have focused on the ion channels and pumps acquired or lost during VSMC switch to the synthetic phenotype and their role in proliferation [14,32,74,82]. The transcription factors that control the gene regulation of these proteins are starting to emerge [32,75,149,150,160,162].…”

Calcium Cycling in Synthetic and Contractile Phasic or Tonic Vascular Smooth Muscle Cells

“…On the other hand, the expression of the molecular entities modulating the plasma membrane Ca 2+ -release activated Ca 2+ channel (CRAC) functioning [57,69] are highly up-regulated; we refer to the proteins forming the CRAC complex or regulating the ICRAC (such as ORAI1-3 and STIM1) and to the IP3R [70,71]. Besides, the expression of TRPCs family members, particularly TRPC1 and TRPC6, dramatically increases in synthetic cells leading to the increase of whole cell Ca 2+ current [72,73].…”