Abstract
Kidneys metabolize arterial cAMP to adenosine by the sequential actions of ectophosphodiesterase (cAMP → AMP) and ecto-5′-nucleotidase (AMP → adenosine). In this study, we demonstrated that etheno-AMP (fluorescent AMP analog) is nearly completely converted to etheno-adenosine during a single pass through the isolated, perfused rat kidney indicating that ecto-5′-nucleotidase is not rate limiting. Therefore, we examined the regulation of ectophosphodiesterase. In 17 control kidneys pretreated with α,β-methylene-adenosine-5′-diphosphate (inhibitor of ecto-5′-nucleotidase to prevent AMP metabolism; 100 μM), addition of cAMP (10 μM) to the perfusate increased renal venous AMP from 0.6 ± 0.2 to 3.5 ± 0.5 nmol/min/g. Pretreatment of kidneys with phorbol 12-myristate 13-acetate (protein kinase C activator; 7.5 nM) increased renal vascular resistance and significantly augmented the cAMP-induced increase in renal venous AMP (from 0.8 ± 0.2 to 5.2 ± 0.7 nmol/min/g with cAMP). Pretreatment of kidneys with bisindolymaleimide I (protein kinase C inhibitor; 3 μM) abrogated the effects of phorbol 12-myristate 13-acetate on both renovascular resistance and cAMP conversion to AMP. Compared with kidneys from rats fed a high-sodium diet (3.15%) for 1 week, in kidneys from rats fed a low-sodium diet (0.03%) the conversion of cAMP to AMP was attenuated (high sodium, from 1.0 ± 0.1 to 4.6 ± 0.4 nmol/min/g with cAMP; low sodium, from 0.5 ± 0.04 to 2.6 ± 0.04 nmol/min/g with cAMP). We conclude that the renal vasculature efficiently converts AMP to adenosine and that metabolism of cAMP to AMP is rate limiting and regulated acutely by protein kinase C and chronically by sodium intake.
Footnotes
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This study was supported by the National Institutes of Health Grants HL69846 and DK68575.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.107.134445.
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ABBREVIATIONS: PDE, phosphodiesterase; ecto-5′-NT, ecto-5′-nucleotidase; ecto-PDE, ectophosphodiesterase; AMPCP, α,β-methylene-adenosine-5′-diphosphate; PMA, phorbol 12-myristate 13-acetate: Ang II, angiotensin II; AVP, arginine vasopressin; LSD, least significant difference; PKC, protein kinase C.
- Received November 17, 2007.
- Accepted January 24, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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