Chronic hypoxia up-regulates expression of adenosine A 1 receptors in DDT 1-MF2 cells

Abstract

As the first step to understand how chronic hypoxia might regulate smooth muscle function in health and disease, we have employed an established immortalised cell model of smooth muscle, DDT 1-MF2 cells, to address the hypothesis that adenosine A 1 receptor density is modulated by O 2 availability. Maximal specific binding ( B max) of the selective adenosine A 1 receptor antagonist, [ 3 H ]-DPCPX, to cell membranes increased 3.5-fold from 0.48±0.02 pmol/mg to 1.7±0.5 pmol/mg protein after 16 hr of hypoxia and this effect was not accompanied by any statistically significant changes in either binding affinity (0.84±0.2 nM vs. 1.2±0.3 nM) or Hill coefficient (1.1±0.1 vs. 0.99±0.03). Hypoxia-evoked increases in membrane receptor density were paralleled in intact DDT 1-MF2 cells. In addition, the increase in [ 3 H ]-DPCPX binding to intact cells was inhibited by co-incubation during hypoxia with the translational inhibitor cycloheximide, the transcriptional blocker actinomycin D and the NFκB inhibitor sulphasalazine. Together, these data show that adenosine A 1 receptor density is modulated, at least in part, by O 2-dependent activation of the transcription factor NFκB and adds to the list of processes dynamically regulated by ambient oxygen availability. Since hypoxia is an initiating factor in acute renal failure, similar changes in transcription may account for up-regulation of adenosine A 1 receptors noted previously in the renal vasculature of rats with acute renal failure.