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

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. 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. 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. 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.