Phosphatidates inhibit vasopressin-induced water transport via protein kinase C activation

Abstract

Phosphatidic acid (PA), best known as an intermediate of phosphatidylinositol bisphosphate (PIP2) turnover, inhibits vasopressin (AVP)-induced increase in hydraulic conductivity (Lp) in rabbit cortical collecting ducts (CCD) perfused in vitro (Ando, Y., H. R. Jacobson, and M. D. Breyer, J. Clin. Invest. 80: 590, 1987). The present study addresses the mechanism(s) responsible for this action of PA. In control experiments, 10 microU/ml AVP (23 pM) increased Lp of CCDs from a basal of 4.9 +/- 0.4 X 10(-7) cm.atm-1.s-1 to a peak of 171.2 +/- 4.6 X 10(-7) cm.atm-1.s-1. Basolateral pretreatment of the tubule with PA (25 micrograms/ml) suppressed AVP-induced increase in peak Lp by 45.0%. This suppression was not attenuated by 5 microM indomethacin pretreatment. L-alpha-dipalmitoyl(C16) PA (DPPA, 25 micrograms/ml), an arachidonate-free synthetic PA, inhibited peak Lp by 79.0%, whereas another synthetic PA with shorter fatty acid (C12), L-alpha-dilauroyl PA (DLPA, 25 micrograms/ml), had no significant effect on AVP-induced peak Lp. In the presence of 100 nM staurosporine, a protein kinase C (PKC) inhibitor, the inhibition by PA and DPPA on AVP-induced peak Lp were abolished. Furthermore, another PKC inhibitor, 100 microM 1-(5-isoquiniline-sulfonyl)-2-methylpiperzine, also reversed the DPPA-induced inhibition of AVP action. In separate experiments using fura-2-loaded isolated perfused CCDs, however, neither PA nor DPPA caused a significant increase in intracellular free Ca2+ concentration [( Ca2+]i). Taken together, in CCD, PA-induced inhibition of AVP action is primarily mediated by PKC but not by an increased [Ca2+]i or the production of arachidonate metabolites, such as prostaglandins. Thus the PA-induced activation of PKC does not seem to involve the classic pathway for PKC activation, breakdown of PIP2.