Effect of chronic renal failure on Ca2+ ATPase of brain synaptosomes.
Chronic renal failure (CRF) is associated with a sustained rise in the concentration of cytosolic calcium [( Ca2+]i) of brain synaptosomes. This was attributed to secondary hyperparathyroidism where the excess blood levels of parathyroid hormone ( PTH) augment calcium entry into synaptosomes. However, for such an effect of PTH to cause a sustained rise in [Ca2+]i, calcium extrusion out of synaptosomes should be impaired. The study presented here examined the effect of CRF with and without (CRF-PTX) excess PTH and the treatment of CRF rats with verapamil (V) on the Vmax and Km for calcium of synaptosomal Ca2+ ATPase, an enzyme that plays an important role in pumping calcium out of the synaptosomes. The Vmax of synaptosomal Ca2+ ATPase in CRF rats was significantly (P less than 0.01) lower than that of normal, CRF-PTX, CRF-V, and normal-V rats. However, the values in CRF-V were still below normal (P less than 0.05). There were no significant differences in the Km for calcium of synaptosomal Ca2+ ATPase among the five groups of animals. [Ca2+]i was significantly (P less than 0.01) higher in synaptosomes of CRF rats than in normal, CRF-PTX, CRF-V, and normal-V animals, and the values among the latter four groups were not different. The data demonstrate that the activity of synaptosomal Ca2+ ATPase is reduced in CRF rats, and this derangement is related to the excess PTH. This derangement in Ca2+ ATPase activity plays an important role in the genesis of the sustained elevation of synaptosomal [Ca2+]i in CRF.[1]References
- Effect of chronic renal failure on Ca2+ ATPase of brain synaptosomes. Hajjar, S.M., Smogorzewski, M., Zayed, M.A., Fadda, G.Z., Massry, S.G. J. Am. Soc. Nephrol. (1991) [Pubmed]
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