Alpha7-type acetylcholine receptor localization and its modulation by nicotine and cholesterol in vascular endothelial cells

AYALA PEÑA, V.B.; BONINI, I.C.; ANTOLLINI, S.S.; BARRANTES, F.J.

JOURNAL OF CELLULAR BIOCHEMISTRY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Lugar: New York; Año: 2011 vol. 112 p. 3276 - 3288

0730-2312

The neuronal-type alpha7 nicotinic acetylcholine receptor (alpha7AChR) is also found in various non-neural tissues, including vascular endothelium, where its peculiar ionotropic properties (high Ca2 permeability) and its supervening Ca2 -mediated intracellular cascades may playimportant roles in physiology (angiogenesis) and pathology (inflammation and atherogenesis). Changes in molecular (up-regulation, affinity, and conformational states) and cellular (distribution, association with membranes) properties of the alpha7AChR related to angiogenesis (woundrepaircell migration) and atherogenesis (alterations in cholesterol content) were studied in living endothelial cells, with the aim of determining whether such changes constitute early markers of inflammatory response. The combination of pharmacological, biochemical, and fluorescence microscopy tools showed that a7AChRs in rat arterial endothelial (RAEC) and human venous endothelial (HUVEC) cells occur at extremely low expression levels (approx. 50 fmol/mg protein) but undergo agonist-induced up-regulation at relatively high nicotine concentrations (approx. 300-fold with 50 mMligand), increasing their cell-surface exposure. When analyzed in terms of cold Triton X-100 solubility and subcellular distribution, alpha7AChRs occur in the ??non-raft?? subcellular membrane fractions. Acute cholesterol depletion reduced not only cholesterol levels but also the number of cell-surface a7AChRs. Nicotine exposure markedly stimulated cell migration and accelerated wound repair, which drastically diminished in cells deprived of the sterol. The angiogenic effect of nicotine appears to be synergistic with cholesterolcontent. Finally, the apparent KD of a7AChRs for the open-channel blocker crystal violet was found to be approx. 600-fold lower in receptorenriched membranes obtained from up-regulated HUVEC.