ATP/Mg2+-dependent cardiac transport system for glutathione S-conjugates. A study using rat heart sarcolemma vesicles.
In the present study, the transport of glutathione S-conjugate across rat heart sarcolemma has directly been proved to be an ATP-dependent process. Incubation of sarcolemma vesicles with S-(2,4-dinitrophenyl)glutathione (DNP-SG) in the presence of ATP resulted in a substantial uptake of DNP-SG into the vesicles; Mg2+ was required for ATP-stimulated transport. The rate of glutathione S-conjugate uptake was saturated with respect to ATP and DNP-SG concentrations with apparent Km values of 30 microM for ATP and 20 microM for DNP-SG. However, other nucleoside triphosphates, viz. GTP, UTP, CTP, and TTP, did not stimulate the transport effectively. The ATP-stimulated DNP-SG uptake was not affected by ouabain, EGTA, or by valinomycin-induced K+-diffusion potential, suggesting that Na+,K+-and Ca2+-ATPase activities as well as the membrane potential are not involved in the transport mechanism. ATP could not be replaced by ADP, AMP, or by ATP analogues, adenosine 5'-(beta,gamma-methylene) triphosphate and adenosine 5'-(beta,gamma-imino)triphosphate. From these observations, it is proposed that hydrolysis of gamma-phosphate of ATP is essential for the transport mechanism. The transport of DNP-SG by the sarcolemma vesicles, on the other hand, was inhibited by several different types of glutathione S-conjugates including 4-hydroxynonenal glutathione S-conjugate and leukotriene C4, and not by GSH. The transport system is suggested to have high affinities toward glutathione S-conjugates carrying a long aliphatic carbon chain (n greater than 6) and may play an important role in elimination of naturally occurring glutathione S-conjugates, such as leukotriene C4.
Ishikawa
T
T
Department of Biochemistry, Osaka University Medical School, Japan.
D000227:Adenine Nucleotides / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism / Q000494:pharmacology / Q000031:analogs & derivatives; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009711:Nucleotides / Q000494:pharmacology; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000378:metabolism*
D000227:Adenine Nucleotides; D009711:Nucleotides; C030190:S-(2,4-dinitrophenyl)glutathione; D000255:Adenosine Triphosphate; D005978:Glutathione; D008274:Magnesium