Ontogeny of the cell outward dopamine transporter in canine renal tissues

The present work has determined the activities of aromatic L-amino acid decarboxylase (AAAD) and evaluated the presence of an active transport system for dopamine in renal tissues of developing dogs (newborn puppies less than 24 hours after birth, animals at the age of 10 days and 2 months) and adult animals. AAAD activity (Vmax, in pmol/mg protein/h) as determined in kidney homogenates was found to be in the adult dog kidney (Vmax = 3216 +/- 268) higher (p < 0.05) than that occurring in the three other groups of animals; no significant difference on AAAD activity was observed between the 10 day-old (Vmax = 1139 +/- 185) and the 2 month-old dogs (Vmax = 783 +/- 23). AAAD activity in newborn puppies (Vmax = 259 +/- 40) was markedly lower than in the three other groups. A considerable amount of the total dopamine formed from added L-DOPA in kidney slices, depending on the age, was found to escape into the incubation medium. The application of the Michaelis-Menten equation to the net transport of newly-formed dopamine has allowed the identification of a saturable (carrier-mediated transfer) and a non-saturable component (diffusion). The Vmax (nmol/g/15 min), Km (microM) values for the saturable component and diffusion constant (mumol-1) were as follows: adult (Vmax = 112 +/- 16; Km = 319 +/- 35; diffusion constant = 0.0009 +/- 0.0001), 2 month-old (Vmax = 19 +/- 5; Km = 48 +/- 14; diffusion constant = 0.0007 +/- 0.0002), 10 day-old (Vmax = 25 +/- 3; Km = 69 +/- 20; diffusion constant = 0.0033 +/- 0.0007) and newborn (Vmax = 6 +/- 1; Km = 16 +/- 6; diffusion constant = 0.0095 +/- 0.0010). In conclusion, renal AAAD develops with age, though some AAAD activity can already be detected at birth.(ABSTRACT TRUNCATED AT 250 WORDS)