Abstract
Cyclooxygenase-2 (COX-2) is the key enzyme regulating the production of prostaglandins (PGs), and is expressed in the kidney macula densa (MD) cells. COX-2-derived PGE2 stimulates the release of renin from the granular cells of afferent arterioles, especially during volume depletion. In the present study, newly established mouse macula densa cells (NE-MD) were used to directly determine whether COX-2 gene expression was regulated by low luminal [NaCl] concentration and other cellular signals, such as cAMP and Ca2+. Results. (1) Microarray analysis revealed that expression of COX-2 and EP4 mRNAs was increased 1.3- and 1.5-fold, respectively, in the presence of 12 μM furosemide (an inhibitor of Na+-K+-2Cl− cotransporter). (2) Real-time RT-PCR showed a significant increase in COX-2 mRNA when NE-MD cells were incubated with low [Cl−] solution, furosemide or forskolin. Low [Cl−]-induced increase in COX-2 mRNA expression was completely reversed by either EIPA or BAPTA-AM (a membrane-permeable Ca2+ chelator). (3) RT-PCR revealed that NE-MD cells did not express EP1-EP3 receptors, but EP4 receptor. (4) Addition of PGE2 to the medium elevated the intracellular cAMP concentration, which then resulted in the increase of COX-2 mRNA expression. (5) Treatment of NE-MD cells with low [Cl−] increased PGE2 generation. Conclusions. These results suggest that COX-2 gene expression may be regulated by either extracellular [NaCl] or changes in the levels of intracellular cAMP, pH, and Ca2+. [NaCl] -inducible stimulation of COX-2 may influence the tubuloglomerular feedback by generating PGE2. [J Physiol Sci. 2008;58 Suppl:S114]
