Preglomerular microcirculation expresses the cAMP-adenosine pathway

The purpose of this study was to investigate whether the extracellular cAMP -adenosine pathway (i.e., transport of cAMP out of cells followed by extrac ellular conversion of cAMP to adenosine) exists in preglomerular microvesse ls (PGMVs). Incubation of PGMVs for 1 h with 30 mu M cAMP increased the amo unt of extracellular adenosine from 163 +/- 18.6 (n = 18) to 9810 +/- 604 ( n = 12) pmol/mg of protein (P < 10(-6)). The phosphodiesterase inhibitor 3- isobutyl-1-methylxanthine (IBMX; 1 mM; n = 6) and the ecto-phosphodiesteras e inhibitor 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX; 1 mM; n = 6) signi ficantly (P < 10(-6) and P < 10(-5), respectively) reduced the cAMP-induced increase in extracellular adenosine. Incubation of PGMVs for 1 h with isop roterenol (beta-adrenoceptor agonist; 1 mu M) 1 IBMX (0.1 mM) increased the amount of extracellular cAMP from 0.800 +/- 0.047 to 22.3 +/- 2.20 pmol/ m g of protein (P < 10(-6); n = 41). In PGMVs incubated with isoproterenol (1 mu M) 1 IBMX (0.1 mM) for 1 h, there was a significant (P < 10(-4)) linear (r(2) = 0.6) relationship between intracellular and extracellular cAMP lev els. Incubation of PGMVs for 1 h with 1 mu M isoproterenol increased the am ount of extracellular adenosine from 163 6 18.6 (n = 18) to 297 +/- 38.3 (n = 12) pmol/ mg of protein (P = .002). Propranolol (beta-adrenoceptor antag onist; 1 mu M; n = 7), IBMX (1 mM; n = 14), and DPSPX (1 mM; n = 12) blocke d (P = .037, P = .015, and P = .026, respectively) isoproterenol-induced in creases in extracellular adenosine. Conclusions: PGMVs transport endogenous cAMP to the extracellular compartment and metabolize extracellular cAMP to adenosine. This pathway can increase extracellular levels of adenosine dur ing beta-adrenoceptor activation of adenylyl cyclase.