The inhibition of mitochondrial calcium transport by lanthanides and ruthenium red

Abstract

An EGTA (ethanedioxybis(ethylamine)tetra acetic acid) quench technique was developed for measuring initial rates of 45Ca2+ transport by rat liver mitochondria. This method was used in conjunction with studies of Ca2+ stimulated respiration to examine the mechanisms of inhibition of Ca2+ transport by the lanthanides and Ruthenium Red. Ruthenium Red inhibits Ca2+ transport non competitively with K(i) 3 x 10-8M, with 0.08 nmol of carrier specific binding sites/mg of protein. The inhibition by La3+ is competitive (K(i)= 2 x 10-8M), with the concentration of lanthanide sensitive sites being less than 0.001 nmol/mg of protein. A further difference between their modes of action is that lanthanide inhibition diminishes with time whereas that by Ruthenium Red does not. Binding studies showed that both classes of inhibitor bind to a relatively large number of external sites (probably identical with the 'low affinity' Ca2+ binding sites). La3+ competes with Ruthenium Red for most of these sites, but a small fraction of the bound Ruthenium Red (less than 2nmol/mg of protein) is not displaced by La3+. The results are discussed in relation to possible models for a Ca2+ carrier. Show more