engleski

Phospholipase D is a new transduction pathway for angiotensin II in proximal tubules

The products arising from phospholipid hydrolysis act as second messengers to regulate cellular functions. The purpose of the present study was first to find out whether phospholipase D (PLD) represented a transduction pathway for angiotensin II (ANG II) receptors in suspension of rat kidney cortical tubules freshly isolated. The second aim of the work was to determine whether PLD could participate to protein kinase C (PKC) activation and be involved in the regulation of the activity of the luminal Na+/H+ antiporter using bacterial PLD from Streptomyces species. PLD activity was assessed by the accumulation of  3H phosphatidic acid (PtdOH) and of  3H phosphatidylethanol (PtdEtn), when tubules labelled with  3H lysoPAF were incubated in the presence of 1% ethanol. Luminal membrane vesicles (LMV) were prepared by the Mg++ precipitation method. The abundance of PKC was studied by Western blot and Na+/H+ activity by measurement of the initial rate of 22 Na uptake stimulated by proton gradient and sensitive to ethylisopropilamiloride (EIPA, 10-4). ANG II elicited a time- and dose-dependent accumulation of  3H PtdOH and  3H PtdEt with an increase of 30  9 and 41  9 % of controls respectively, for the application of 10-7 M for 2.5 minutes. ANG II induced PLD activation was insensitive to two dissimilar PKC inhibitors GF 109203X (10-5 M) and calphostin C (10-6 M). When exogenous bacterial PLD (1U/ml, 10 minutes) was applied to the tubule suspension, the abundance of PKC  was increased in LMV subsequently isolated (30  7 %) and Na+/H+ activity was reduced to 90  2% of controls. The inhibition was sensitive to the PKC inhibitor GF 109203X (10-5 M). PLD activation appeared as a new signalling pathway for ANG II in kidney cortical tubules. Data obtained with bacterial PLD suggested that, this pathway could be, at least in part, involved in PKC  activation and in PKC mediated inhibition of the luminal Na+/H+ exchange NHE3.

Phospholipase D; angiotensin II; proximal tubules

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