Differential coupling of the P2Y1 receptor to Gα14 and Gαq/11 proteins during the development of the rat salivary gland

In rat submandibular gland (SMG), the P2Y(1) receptor (P2Y(1)R) mediates increases in the intracellular calcium concentration, [Ca2+](i) that diminish as the animal ages from 1 to 4-6 weeks. However, P2Y(1)R mRNA levels do not change with age, suggesting that the age-dependent decrease in the [Ca2+](i) response to P2Y(1)R agonists may be due to alterations in the activity of a component of the P2Y(1)R signalling pathway. Objectives: To assess whether the decrease in P2Y(1)R-mediated intracellular calcium signalling in SMG cells as rats age is due to a decrease in P2Y(1)R coupling to G proteins or to a decrease in the expression of a cognate G protein. Design: SMG cells were isolated from Sprague-Dawley rats. P2Y(1)R function was assessed by measuring 2-MeSADP-induced increases in [Ca2+](i) and ERK1/2 activation. P2Y(1)R-mediated activation of G proteins was determined by the [S-35]GTP gamma S binding assay. G(q) protein expression was determined by RT-PCR, Northern, and Western analysis. Results: In SMG cells from 1-week-old rats, two bands (52 and 42 kDa) were detected using anti-G alpha(14) antibody, whereas in SMG cells from 4- to 6-week-old rats only the 42 kDa band was detected. Furthermore, 2-MeSADP-induced GTP gamma S-35 binding to G alpha(14) and G alpha(q/11) decreases in SMG cells from 4- to 6-week-old rats as compared to 1-week-old rats.