The role of calcium (Ca$\sp{2+})$ in numerous cell functions has been firmly established. Free intracellular Ca$\sp{2+}$ interacts with calcium binding proteins (CaBP's), such as calmodulin (CaM), which serve as intracellular 'calcium receptors' to transmit the Ca$\sp{2+}$ signal. 1,25-dihydroxyvitamin D$\rm\sb3\ \lbrack1,25(OH)\sb2D\rbrack,$ acts through its receptor (VDR) to maintain plasma calcium homeostasis and also increase tissue levels of several vitamin-D regulated CaBP's Previous studies have provided evidence for 1,25(OH)$\sb2$D regulated CaM-binding proteins in the rat kidney cytosol. The main objectives of this dissertation were to establish the principal CaMBP's stimulated by 1,25(OH)$\sb2$D in the rat kidney, identify some of their functional characteristics, and investigate their relationship to other effects of 1,25(OH)$\sb2$D in this system Protracted treatment (7d) of vitamin D-deficient rats with 100ng 1,25(OH)$\sb2$D specifically stimulated four principal CaMBP's (CaMBP-D145, CaMBP-D117, CaMBP-D98, and CaMBP-D77) in the rat kidney cytosol. CaMBP-D98 and CaMBP-D77 were predominantly cytosolic, whilst CaMBP-D117 was present in both cytosolic and microsomal fractions. CaMBP-D145 was present in all the subcellular fractions, but only the cytosolic CaMBP-D145 was 1,25(OH)$\sb2$D-stimulated. Membrane localization studies confirmed the exclusive cytosolic localization of CaMBP-D77 and CaMBP-D98, whilst CaMBP-D117 and CaMBP-D145 were present in both membrane and cytosolic fractions. A vitamin D-independent 145 kDa CaMBP that co-migrated with the CaMBP-D145 was present in the basolateral membrane preparation. CaMBP-D115, CaMBP-D98, and CaMBP-D77 were predominantly localized to the distal tubule, whilst CaMBP-D145 was present in both nephron segments. The time course and dose responsiveness of 1,25(OH)$\sb2$D-stimulation of the different CaMBP-D's was not significantly different from that of 1,25(OH)$\sb2$D-induced upregulation of VDR which is considered a physiological effect of 1,25(OH)$\sb2$D in the kidney. Compared with the other effects of 1,25(OH)$\sb2$D in the rat kidney and plasma, there was a hierarchy of sensitivity to 1,25(OH)$\sb2$D in the following order: CaBP-D28K $>$ plasma calcium $\sim$ renal alkaline phosphatase $>$ VDR upregulation/CaMBP-D stimulation The results are exciting because they suggest that the Ca-CaM signal transduction pathway may, via changes in activity of some acceptor proteins, effect some of the biological effects of 1,25(OH)$\sb2$D. The results are also important in serving as a foundation for further studies into this intriguing field / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_25091 |
| Date | January 1995 |
| Contributors | Siaw, Emmanuel Okoree K (Author), Walters, Marian R (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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