Received for publication January 3, 2007.
Revised February 12, 2007.
Accepted for publication February 12, 2007.

CHARACTERIZATION OF RENAL ECTO-PHOSPHODIESTERASE

Abstract

In kidneys, stimulation of adenylyl cyclase causes egress of cAMP, conversion of cAMP to AMP by ecto-phosphodiesterase and metabolism of AMP to adenosine by ecto-5'-nucleotidase. Although much is known about ecto-5'-nucleotidase, the renal ecto-phosphodiesterase remains uncharacterized. We administered cAMP (10 µmol/L in the perfusate) to 12 different groups of perfused kidneys. AMP was measured in perfusate using ion trap mass spectrometry. In control kidneys (n=17), basal renal secretion rate of AMP was 0.49 ± 0.08 and increased to 3.0 ± 0.2 nmoles AMP per gram kidney weight per min during adminstration of cAMP. A broad spectrum PDE inhibitor (1,3-isobutyl-1-methylxanthine, 300 µmol/L, n=6) and an ecto-phosphodiestease inhibitor (1,3-dipropyl-8-sulfophenylxanthine, 1 mmol/L, n=6) significantly attenuated cAMP-induced AMP secretion by 60% and 74%, respectively. Blockade of PDE1 (8-methoxymethyl-3-isobutyl-1-methylxanthine, 100 µmol/L), PDE2 (erythro-9-(2-hydroxy-3-nonyl)-adenine, 30 µmol/L), PDE3 (milrinone, 10 µmol/L; cGMP, 10 µmol/L), PDE4 (RO 20-1724, 100 µmol/L), PDE5 and PDE6 (zaprinast, 30 µmol/L) and PDE7 (BRL-50481, 10 µmol/L) did not alter renal ecto-phosphodiesterase activity. Administration of a concentration (100 µmol/L) of dipyridamole that blocks PDE8 inhibited ecto-phosphodiesterase activity (by 44%). However, a lower concentration of dipyridamole (3 µmol/L) that blocks PDE9, PDE10 and PDE11, but not PDE8, did not inhibit ecto-phosphodiesterase activity. These data support the conclusion that renal ecto-phosphodiesterase activity is not mediated by PDE1, PDE2, PDE3, PDE4, PDE5, PDE6, PDE7, PDE9, PDE10 or PDE11, and is inhibited by high concentrations of dipyridamole. Ecto-phosphodiesterase has some pharmacological characteristics similar to PDE8.

Key words: AMP, adenosine, cAMP, cAMP-adenosine pathway, ecto-5'-nucleotidase, ecto-phosphodiesterase

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