Document Detail


The ionic control of 1,25-dihydroxyvitamin D3 synthesis in isolated chick renal mitochondria. The role of calcium as influenced by inorganic phosphate and hydrogen-ion.
MedLine Citation:
PMID:  236327     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Isolated kidney mitochondria prepared from Vitamin D-deficient chicks catalyze the conversion of 25-hydroxyvitamin D3 to 1,25 dihydroxyvitamin D3. It wasfound that changes in the concentrations of Ca-2plus, HPO4-2minus, and Hplus altered synthesis in an interrelated fashion. Increasing the Ca-2plus concentration from 10-6 to 10-5 M caused a four- to fivefold increase in 1 alpha-hydroxylase activity when the medium pH was between 6.5 and 7.0. increasing the [Ca2+] to 10-4 M caused to furhter stimulation. At higher pH values, Ca-2plus had little effect upon 1 alpha-hydroxylase activity. In the absence of calcium [Ca2+] less than or equal to 10-7 M), a change in pH from 6.5 to 7.1 had no effect upon 1 alpha-hydroxylase activity in the presence of 10-5 M calcium, increasing the medium pH had a biphasic effect. An increase in pH from 6.5 to 6.9 caused a 1.5-fold increase in 1 alpha-hydroxylase activity, but a further increase of the pH to 7.1 caused a profound decrease in rate of hydroxylation to approximately 20% of the peak value. Neither 10-5 M LaC13 nor 10 mug/ml of oligomycin altered the effects of Ca2+ upon hydroxylate activity. However, the effect of calcium was blocked by 2.5 times 10-5 M ruthenium red, 0.83 mug/ml of antimycin A, and 500 muM dinitrophenol. The clcium ionophore, A23187, decreased but did not prevent the stimulatory effect of calcium. These data are consistent with the concept that the [Ca2+ in the mitochondrial matrix space is of importance in regulating the 1 alpha-hydroxylase. Phosphate exerted a biphasic effect on 1,25(OH)2D3 production with maximal stimulation (approximately twofold) at 1-3 mM. Calcium enhanced the stimulation by phosphate at all concentrations studied. The presence of potassium modified the interrelated effects of calcium and phosphate in two ways: 10-3 M calcium blocked the stimulation by phosphate; and in the presence of phosphate, 10-3 M calcium resulted in less 1,25(OH)2D3 production by production by isolated mitochondria are qualitatively similar to the effects of these ions on 1,25(OH)2D3 production yb isolated renal tubules.
Authors:
D D Bikle; E W Murphy; H Rasmussen
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of clinical investigation     Volume:  55     ISSN:  0021-9738     ISO Abbreviation:  J. Clin. Invest.     Publication Date:  1975 Feb 
Date Detail:
Created Date:  1975-07-14     Completed Date:  1975-07-14     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  7802877     Medline TA:  J Clin Invest     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  299-304     Citation Subset:  AIM; IM    
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MeSH Terms
Descriptor/Qualifier:
Animals
Antimycin A / pharmacology
Calcium / antagonists & inhibitors,  pharmacology*
Chickens
Diet
Dihydroxycholecalciferols / biosynthesis*
Dinitrophenols / pharmacology
Hydrogen-Ion Concentration
Hydroxycholecalciferols / biosynthesis*
Kidney / enzymology*,  ultrastructure*
Mitochondria / drug effects,  enzymology*,  metabolism
Mixed Function Oxygenases / metabolism
Oligomycins / pharmacology
Phosphates / pharmacology*
Ruthenium / pharmacology
Vitamin D Deficiency / metabolism
Chemical
Reg. No./Substance:
0/Dihydroxycholecalciferols; 0/Dinitrophenols; 0/Hydroxycholecalciferols; 0/Oligomycins; 0/Phosphates; 642-15-9/Antimycin A; 7440-18-8/Ruthenium; 7440-70-2/Calcium; EC 1.-/Mixed Function Oxygenases
Comments/Corrections

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