The mitochondrial high-capacity low-affinity (+/-)-[3H]nitrendipine binding site is regulated by nucleotides

The high-capacity, low-affinity (+/-)-[3H]nitrendipine binding site in the inner mitochondrial membrane from guinea-pig heart is regulated by purine and pyrimidine nucleotides. The rank order in (+/-)-[3H]nitrendipine binding inhibition assays (with decreasing potency) was: ATP (IC50 11.8 microM) = adenosine 5'-O-(2-thiotriphosphate (ATP gamma S) greater than 5'-adenylylimidodiphosphate (AppNHp) greater than ADP much greater than GTP = ITP = CTP greater than UTP greater than guanosine 5'-tetraphosphate (GT4P) greater than guanosine 5'-O-(2-thiotriphosphate) (GTP gamma S) greater than 5'-guanylylimidodiphosphate (GppNHp) greater than IDP greater than CDP greater than GDP. There was no effect of AMP, adenosine 3':5'-cyclic monophosphate (cAMP), adenosine, UDP, NAD, and NADP. The ATP effect was fully reversible upon wash-out. Adenine nucleotides and analogs had a (+/-)-[3H]nitrendipine binding inhibition profile in mitochondrial membranes from guinea-pig liver or kidney similar to that obtained in heart mitochondrial membranes. In heart mitochondria, 0.3 mM ATP decreased the Bmax from 1.69 +/- 0.04 nmol/mg protein to 0.73 +/- 0.24 nmol/mg protein whilst it decreased the KD only moderately, from 521 +/- 50 to 352 +/- 43 nM, in equilibrium saturation studies. In kinetic studies, ATP slowed down the dissociation rate of the (+/-)-[3H]nitrendipine binding site complex from 0.016 +/- 0.004 to 0.0042 +/- 0.0002 min-1 but it also decreased the association rate constant from 1.52 +/- 0.15 to 0.41 +/- 0.28 10(4).M-1.min-1, yielding a kinetically determined KD (1024 nM) identical to the control KD (1053 nM).(ABSTRACT TRUNCATED AT 250 WORDS)