Non-phosphorylating respiration (VO2) is primarily controlled by proton (H+) leak across the inner mitochondrial membrane (IMM). Recently discovered genes whose predicted amino acid sequences place them in the same family as uncoupling protein-1 (UCP-1) may be the physical basis for this leak. To determine if the leak in isolated liver (L) and skeletal muscle (SM) mitochondria is regulated similarly to UCP-1, we measured effects of nucleotides on non-phosphorylating VO2 with a Clark electrode and IMM voltage (IMMV) with the voltage sensitive dye JC-1 (0.47μM). Mitochondria were incubated at 37C in a KCl based reaction buffer (pH 6.9) containing 3 μg/mL oligomycin, 5 μM rotenone, and 5 mM succinate. Nucleotide effects on VO2 and IMMV are summarized in the table; percents are peak changes from the succinate induced value. GTP ATP AMP CTP CMP L VO2 -20% -97%* (11.0) -13% -90%* (14.6) +75%* (4.43) L IMMV ND -88%* (12.5) -27%* -84%* (14.1) -17%* SM VO2 -23%* -99%* (11.2) -34%* -79%* (16.3) +15%* (4.16) SM IMMV ND -96%* (11.1) -36%* -86%* (15.6) -20%* * p<0.05 for effect of the nucleotide (0.8-21 mM) by one way ANOVA; IC50 (ATP, CTP) and EC50 (CMP) values in mM in ( ) ; ND=not determined. We conclude that VO2 inhibition by ATP, CTP, and AMP reflects respiratory chain rather than leak inhibition (i.e., IMMV doesn't increase). In contrast, CMP stimulation of VO2 and inhibition of IMMV suggest possible CMP regulation of H+ leak in L and SM mitochondria. Regulation of this leak thus differs from that mediated by UCP-1.
|Original language||English (US)|
|State||Published - Mar 20 1998|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology