Maturational changes in rabbit renal cortical phospholipase A2 activity

Ji Nan Sheu, Michel Baum, Elizabeth W. Harkins, Raymond Quigley

Research output: Contribution to journalArticle

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Abstract

Several studies have demonstrated that the neonatal kidney has a markedly attenuated response to parathyroid hormone (PTH); however, the cause for this blunted response is unknown. PTH stimulated cAMP production by 215 ± 18% in neonatal proximal tubule suspensions compared to a 35 ± 7% increase in adult proximal tubules. Thus, neonatal proximal tubules have functioning PTH receptors and a greater adenylate cyclase response than the adult segment. In adult proximal tubules, PTH stimulates phospholipase A2 (PLA2) activity and the inhibition of Na,K-ATPase activity by PTH is blocked by inhibitors of PLA2. We examined whether maturational changes in renal cortical activity could play a role in the attenuated response to PTH in the neonatal proximal tubule. Com pared to adults, neonates had a lower renal cortical cytosolic PLA2 (cPLA2) activity, assessed as the release of 14C- arachidonic acid (AA) from labeled phosphatidyl choline (0.44 ± 0.10 vs. 0.74 ± 0.06% 14C-AA released/min/mg protein, P < 0.05) and microsomal PLA2 activity (0.32 ± 0.03 vs. 1.20 ± 0.13% 14C-AA released/min/mg protein, P < 0.001). The protein abundance of cPLA2 was not different between the neonatal and adult renal cortex as assessed by immunoblot assay. Thus, the difference in activities must be due to a difference in regulation of cPLA2. Annexin 1 (lipocortin 1) has been shown to inhibit PLA2 activity by binding to phospholipid substrate. Annexin 1 protein abundance was higher in neonatal than in adult renal cortex (P < 0.001). Thus, the lower activity of PLA2 in the neonatal tubules may be due in part to higher expression of annexin 1. PLA2 activation by PTH, 8-bromo-cAMP and PMA was assessed as 3H- AA release from prelabeled suspensions of neonatal and adult proximal tubules. PTH (10-7 M), 8-bromo-cAMP (10-4 M) and PMA (5 x 10-8 M) significantly increased 3H-AA release from adult tubules (P < 0.05) but had no effect on neonatal tubules (P = NS). Thus, PTH, 8-bromo-cAMP and PMA stimulated PLA2 in adult but not neonatal proximal tubules. In conclusion, the maturational changes in renal cortical PLA2 activity may be a factor in the blunted response of neonatal proximal tubules to PTH.

Original languageEnglish (US)
Pages (from-to)71-78
Number of pages8
JournalKidney international
Volume52
Issue number1
DOIs
StatePublished - Jan 1 1997

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Keywords

  • PTH
  • Phospholipase A
  • Proximal tubule
  • Renal cortex

ASJC Scopus subject areas

  • Nephrology

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