Interaction Between TRPC Channel Subunits in Endothelial Cells

Transient Receptor Potential Canonical (TRPC) proteins have been identified in mammals as a family of plasma membrane calcium-permeable channels activated by different kinds of stimuli in several cell types. We have studied TRPC subunit expression in bovine aortic endothelial (BAE-1) cells, where stimulation with basic fibroblast growth factor (bFGF), a potent angiogenetic factor, induces calcium entry carried at least partially by TRPC1 channels. By means of a RT-PCR approach, we have found that, in addition to TRPC1, only TRPC4 is expressed, both at the mRNA and protein level, as confirmed by immunoblotting and immunocytochemical analysis. Because functional TRPC channels are formed by assembly of four subunits in either homo- or heterotetrameric structures, we have carried out immunoprecipitation experiments and showed that TRPC1 and TRPC4 interact to form heteromers in these cells, independently from culture conditions (high or low percent of fetal calf serum, stimulation with bFGF). Moreover, the data show that TRPC subunits are not tyrosine-phosphorylated after bFGF stimulation and they do not co-immunoprecipitate with the type 1 FGF receptor. These results suggest that BAE-1 cells are a suitable model to study function and regulation of endogenous TRPC1/TRPC4 heteromers.     

Catecholamines and Vitiligo

The levels of some catecholamine metabolites, namely homovanillic acid (HVA), vanil-mandelic acid (VMA), 3-methoxytyramine (MT), normetanephrine (NMN), metanephrine (MN), 3,4-dihydroxy mandelic acid (DOMAC), and 3,4-dihydroxy phenylacetic acid (DOPAC), have been evaluated in the 24 hr urines of 150 patients affected with different types of vitiligo and in 50 healthy age-matched individuals. The patients were divided into three groups according to the different phases of the disease. The first group included subjects affected either with the early active phase or with progressive increase in both number and/or the size of previous lesions. The second group included patients in whom no new lesions had appeared for between 4-8 months. In the third group the white areas had been stable for 1-5 years. The first and second groups showed values of HVA and VMA from 4 to 10 times and from ½ to 3 times higher respectively than those of controls, while no significant differences were found between the third group and controls. Our results clearly show that a significant increase of urinary levels of HVA and VMA, deriving respectively from dopamine and from norepinephrine and epinephrine characterizes the onset and the progressive active phases of vitiligo, irrespective of the type of distribution. The increased release of catecholamines from the autonomic nerve endings in the microenvironment of melanocytes in the affected skin areas might be involved in the etiopathogenesis of vitiligo through two main mechanisms: (1) a direct cytotoxic action of catecholamines and/or their o-diphenol catabolites; (2) an indirect action. Skin and mucosa arterioles possess α receptors, activation of which by catecholamine discharge may cause a severe vasoconstriction, leading to epidermal and dermal hypoxia with hyperproduction of toxic oxyradicals generated by different pathways. In both cases a genetic predisposition due to insufficient radical scavengers in the affected areas should be taken into account.