The effects of Mg2+ and adenine nucleotides on the sensitivity of the heart mitochondrial Na+-Ca2+ carrier to extramitochondrial Ca2+. A study using arsenazo III-loaded mitochondria.
The technique of reversible Ca2+-induced permeabilization [Al Nasser & Crompton (1986) Biochem. J. 239, 19-29, 31-40] has been applied to the preparation of heart mitochondria loaded with the Ca2+ indicator arsenazo III (2 nmol of arsenazo III/mg of mitochondrial protein). The loaded mitochondria ('mitosomes') were used to study the control of the Na+-Ca2+ carrier by extramitochondrial Ca2+ mediated by putative regulatory sites. The Vmax. of the Na+-Ca2+ carrier and the degree of regulatory-site-mediated inhibition were similar to normal heart mitochondria. Ca2+ occupation of the sites in mitosomes yields partial inhibition, which is half-maximal with 0.8 microM external free Ca2+. The inhibition consists of a small decrease in Vmax. and a relatively large increase in apparent Km for internal Ca2+. Mg2+ also appears to interact with the sites, but this is largely abolished by ATP and ADP (but not AMP) under conditions in which the free [Mg2+] is maintained constant. The results indicate that the regulatory sites are effective in controlling the Na+-Ca2+ carrier at physiological concentrations of adenine nucleotides, Mg2+, intra- and extra-mitochondrial free Ca2+.
Hayat
L H
LH
Department of Biochemistry, University College London, U.K.
Crompton
M
M
D000227:Adenine Nucleotides / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001150:Arsenazo III / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008929:Mitochondria, Heart / Q000378:metabolism*; D051381:Rats; D019831:Sodium-Calcium Exchanger
D000227:Adenine Nucleotides; D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D001150:Arsenazo III; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium