Effects of nicotine on PTHrP and PTHrP receptor expression in rat coronary endothelial cells.

AIMS The study was aimed to investigate whether nicotine affects endothelial expression of PTHrP and PTHrP receptor, a peptide system involved in endothelial protection against apoptosis. METHODS Isolated and cultured rat coronary endothelial cells were used. Immunoblot techniques were used to study activation of mitogen-activated protein (MAP) kinases and to quantify PTHrP and PTHrP receptor expression. Real-time RT-PCR was used to quantify PTHrP, PTHrP-receptor, bcl-2, and bax mRNA expression. The rate of apoptosis was determined by HOE33258 staining and confirmed by quantification of the bcl-2-to-bax ratio. In vitro data were compared to hearts from rats exposed to cigarette smoking. RESULTS Nicotine induced PTHrP protein expression at nanomolar levels and small increases of PTHrP release (≈8%). Antagonists directed against the α7 subunit of cholinergic receptors, the most prominent isoform, attenuated nicotine-dependent increases of PTHrP expression. This effect of nicotine was p38 MAPK dependent. Nicotine at micromolar concentrations reduced PTHrP receptor expression. In vitro and in vivo we found a correlation between PTHrP receptor expression and bcl-2 expression. CONCLUSION Nicotine induces PTHrP expression in endothelial cells but excessive concentrations of nicotine reduce PTHrP receptor expression thereby attenuating any protective effects of PTHrP against apoptosis.