The effect of lead on the calcium-handling capacity of XXXX heart mitochondria.

@entity141 @entity5910 @entity35 @entity2388 @entity10781
1. Very low concentrations of @entity10781 decrease the capacity of @entity35 heart mitochondria, oxidizing @entity2388 plus @entity5910 , to remove @entity141 from the medium. 2. The primary effect is on the rate of @entity141 sequestration; this is reflected in the overall extent of @entity141 removal. 3. @entity10781 has at least two separate actions. Below about 0.5 nmol/mg of protein, it acts solely by competing with @entity141 (Ki = 0.4 muM); above this concentration it also inhibits the production or use of respiratory energy, so that at 1 nmol of @entity10781 /mg of protein, @entity141 removal is almost completely abolished. 4. @entity10781 inhibits coupled and uncoupled respiratory O2 use by mitochondria oxidizing @entity2388 plus @entity5910 , but at higher concentrations than those that affect @entity141 removal; similar concentrations of @entity10781 inhibit @entity2388 uptake, but not @entity5910 uptake, by the mitochondria. 5. Mg2+ only decreases @entity141 removal by competition, and is a far-less effective competitor than @entity10781 (Ki = 0.15 mM). It is possible that the primary cause of the second effect of @entity10781 is displacement of membrane Mg2+. 6. The consequences of these results are discussed in terms of the possible involvement of heart mitochondria in excitation-contraction coupling, and the @entity10781 levels that might occur in heart tissue in vivo.
