Abstract
The purpose of this study was to investigate whether the extracellular cAMP-adenosine pathway (i.e., transport of cAMP out of cells followed by extracellular conversion of cAMP to adenosine) exists in preglomerular microvessels (PGMVs). Incubation of PGMVs for 1 h with 30 μM cAMP increased the amount 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-phosphodiesterase inhibitor 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX; 1 mM;n = 6) significantly (P < 10−6 and P < 10−5, respectively) reduced the cAMP-induced increase in extracellular adenosine. Incubation of PGMVs for 1 h with isoproterenol (β-adrenoceptor agonist; 1 μM) + IBMX (0.1 mM) increased the amount of extracellular cAMP from 0.800 ± 0.047 to 22.3 ± 2.20 pmol/mg of protein (P < 10−6;n = 41). In PGMVs incubated with isoproterenol (1 μM) + IBMX (0.1 mM) for 1 h, there was a significant (P < 10−4) linear (r2 = 0.6) relationship between intracellular and extracellular cAMP levels. Incubation of PGMVs for 1 h with 1 μM isoproterenol increased the amount of extracellular adenosine from 163 ± 18.6 (n = 18) to 297 ± 38.3 (n = 12) pmol/mg of protein (P = .002). Propranolol (β-adrenoceptor antagonist; 1 μM; n = 7), IBMX (1 mM;n = 14), and DPSPX (1 mM; n = 12) blocked (P = .037, P = .015, and P = .026, respectively) isoproterenol-induced increases 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 during β-adrenoceptor activation of adenylyl cyclase.
Footnotes
-
Send reprint requests to: Edwin K. Jackson, Ph.D., Center for Clinical Pharmacology, University of Pittsburgh Medical Center, 623 Scaife Hall, 200 Lothrop St., Pittsburgh, PA 15213-2582. E-mail:edj+{at}pitt.edu
-
↵1 This study was supported by National Institutes of Health Grants HL55314 and HL35909.
- Abbreviations:
- PGMV
- preglomerular microvessel
- IBMX
- 3-isobutyl-1-methylxanthine
- DPSPX
- 1,3-dipropyl-8-p-sulfophenylxanthine
- Received March 9, 2000.
- Accepted June 12, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|