PDF OnlyCharacterization of dimethylguanosine, phenylethylamine, and phenylacetic acid as inhibitors of Ca2+ ATPase in end-stage renal failure.Jankowski, J; Luftmann, H; Tepel, M; Leibfritz, D; Zidek, W; Schlüter, H Author Information Medizinische Klinik I, Universitäts-Klinik Marienhospital, Ruhr University of Bochum, Herne, Germany. Journal of the American Society of Nephrology : JASN 9(7):p 1249-1257, July 1998. | DOI: 10.1681/ASN.V971249 Free Metrics Abstract The activity of the plasma membrane Ca2+ ATPase of chronic renal failure patients is decreased by circulating inhibitors yet to be characterized. In this study, inhibitors of Ca2+ ATPase were isolated from ultrafiltrate of patients with end-stage renal failure. They were identified as dimethylguanosine, phenylethylamine, and phenylacetic acid by chromatography and mass spectrometry. Ca2+ ATPase activity was measured spectrophotometrically as the difference in hydrolysis of ATP in the presence and absence of Ca2+ with different concentrations of ATP and the isolated substances. All of the identified compounds are sufficiently lipophilic to penetrate the blood-brain barrier and to accumulate in cerebral tissue. The inhibitory effects of these agents were additive. The apparent K(m) values for ATP and Ca2+ were not altered by these substances, suggesting a noncompetitive mechanism of inhibition. In plasma of healthy subjects, the substances were not detectable. The Ca2+ ATPase inhibitors identified may play a role in the pathophysiology of end-stage renal failure and, potentially, in monitoring toxic effects on cellular Ca2+ metabolism in renal failure. Copyright © 1998 The Authors. Published by Wolters Kluwer Health, Inc. All rights reserved.