Regulation of renal ectophosphodiesterase by protein kinase C and sodium diet

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 alpha,beta-methylene-adenosine-5'-diphosphate (inhibitor of ecto-5'-nucleotidase to prevent AMP metabolism; 100 microM), addition of cAMP (10 microM) 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 microM) 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.