HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hutson, S. M. Articles by Lardy, H. A. Search for Related Content PubMed PubMed Citation Articles by Hutson, S. M. Articles by Lardy, H. A. Social Bookmarking                      What's this?

JBC, Vol. 251, Issue 17, 5251-5258, Sep, 1976

Effect of cations and anions on the steady state kinetics of energy-dependent Ca2+ transport in rat liver mitochondria

S. M. Hutson, D. R. Pfeiffer and H. A. Lardy

The divalent cation ionophore A23187 has been used to investigate the kinetics of energy-dependent Ca2+ uptake by rat liver mitochondria under steady state conditions. During A23187-induced cyclic Ca2+ flux, the free Ca2+ concentration is adjusted using [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) buffers. The rate of Ca2+ transport, which is inferred from the rate of succinate oxidation, is a function of the free Ca2+ concentration in the medium. The kinetics are sigmoidal with the free Ca2+ concentration at half-maximal respiratory stimulation (K0.5) equal to 3.1 +/- 0.4 muM at 25 degrees. The maximal Ca2+-stimulated respiratory rate (Vmax) is a function of the ionic composition of the medium. Magnesium and Mg2+ plus phosphate produced a parallel stimulation of the maximal respiration rate whether activated by Ca2+ uptake or by the uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP). In the absence of A23187, Ca:O rations of 4.0 were obtained under most experimental conditions. Magnesium is a potent competitive-like inhibitor, increasing the K0.5 for Ca2+ to 30.0 muM at 2.0 mM MgCl2. Magnesium dramatically decreases the apparent affinity for Ca2+ but does not appear to alter the kinetic mechanism. In contrast, the alkali metal cations are weak inhibitors, at most doubling the K0.5 for Ca2+; however, they antagonized Mg2+ inhibition with an order of effectiveness Li+ greater than or equal to Na+ greater than K+ greater than Rb+ =Cs+. Phosphate and acetate increased the Vmax slightly without altering the K0.5 for Ca2+. Phosphate did not influence the inhibitory effects of Mg2+ or Mg2+ plus K+. This study suggests that during steady state conditions, the maximal rate of Ca2+ accumulation is primarily electron transport-limited. The results are also discussed in terms of a possible physiological role for Mg2+ and K+ in the intracellular regulation of energy-dependent mitochondrial Ca2+ transport in liver.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				N. Shalbuyeva, T. Brustovetsky, and N. Brustovetsky Lithium Desensitizes Brain Mitochondria to Calcium, Antagonizes Permeability Transition, and Diminishes Cytochrome c Release J. Biol. Chem., June 22, 2007; 282(25): 18057 - 18068. [Abstract] [Full Text] [PDF]