Aromatic L-amino acid decarboxylase activity along the rat nephron

Matsuhiko Hayashi, Yasuyoshi Yamaji, Waichi Kitajima, Takao Saruta

Research output: Contribution to journalArticle

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Abstract

Extraneural dopamine is thought to be synthesized by an aromatic L-amino acid decarboxylase (L-AADC) activity in tubular cells. However, the previous histochemical studies of this enzyme's localization in the nephron were not consistent. To determine the localization of L-AADC and whether changes in Na intake regulate this enzyme, L-AADC was measured in microdissected nephron segments from rat kidneys. Dopamine formed by isolated tubules incubated with exogenous L-dopa was quantitated by high-performance liquid chromatography (HPLC) and with the more sensitive radioenzyme assay (REA). L-AADC activity was present only in proximal convoluted (PCT, 208 ± 19 ng·cm-1·h-1) and proximal straight tubules (PST, 81 ± 9 ng·cm-1·h-1), whereas no significant activity was detected in other nephron segments by either HPLC or REA. Maximal velocity (Vmax) of L-AADC in a low-salt diet group (246 ± 4 ng·cm-1·h-1) showed a small but a significant decrease (P ≤ 0.05) compared with control and high-salt diet groups (311 ± 6 and 293 ± 4 ng·cm-1·h-1, respectively), whereas the apparent Michaelis constant (Km) was similar in these three groups. These results show that L-AADC is present only in the PCT and PST of the rat nephron, and suggest that the changes in L-AADC activity may contribute to the regulation of extraneural dopamine production in the kidney during low-salt intake.

Original languageEnglish
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Volume258
Issue number1 27-1
Publication statusPublished - 1990

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Aromatic-L-Amino-Acid Decarboxylases
Carboxy-Lyases
Nephrons
Amino Acids
Dopamine
Salts
High Pressure Liquid Chromatography
Kidney
Sodium-Restricted Diet
Levodopa
Enzymes
Diet

Keywords

  • Decarboxylase
  • Denervation
  • Dopamine
  • Renal tubules
  • Sodium intake

ASJC Scopus subject areas

  • Physiology

Cite this

Aromatic L-amino acid decarboxylase activity along the rat nephron. / Hayashi, Matsuhiko; Yamaji, Yasuyoshi; Kitajima, Waichi; Saruta, Takao.

In: American Journal of Physiology - Renal Fluid and Electrolyte Physiology, Vol. 258, No. 1 27-1, 1990.

Research output: Contribution to journalArticle

Hayashi, Matsuhiko ; Yamaji, Yasuyoshi ; Kitajima, Waichi ; Saruta, Takao. / Aromatic L-amino acid decarboxylase activity along the rat nephron. In: American Journal of Physiology - Renal Fluid and Electrolyte Physiology. 1990 ; Vol. 258, No. 1 27-1.
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