Inhibition of binding of [3H]PN200-110 to membranes from rat brain and heart by ascorbate is mediated by lipid peroxidation.
Ascorbate inhibited the binding of the calcium channel blocker [3H]PN200-110 to membranes prepared from rat brain and heart. The inhibition was increased in the presence of Fe++ and Fe in a dose-dependent manner, with Fe++ being more potent than Fe . Concentration-response curves were biphasic in the absence and presence of 1 microM Fe++, with little inhibition being observed at concentrations of Fe++ below 0.03 mM or above 3 mM. Exposure of membranes to 0.1 mM ascorbate resulted in a 35 to 40% decrease in the density of binding sites for [3H] PN200-110. A further decrease in the density of binding sites of 75 to 80% was observed in the presence of 1 microM Fe++. In the presence of ascorbate a small increase in the Kd for binding of [3H]PN200-110 was also observed. A further increase was observed in the presence of 1 microM Fe++. The concentration-response curves for ascorbate- and ascorbate/iron-induced inhibition of binding were coincident with those for production of malondialdehyde, an index of lipid peroxidation. The effects were eliminated by iron chelators and antioxidants. In both tissues, the time course for ascorbate-induced inhibition of binding of [3H]PN200-110 was coincident with that for formation of malondialdehyde, with a significant lag occurring in experiments with heart membranes but not with brain membranes. Addition of 1 microM FeSO4 increased the rates of inhibition of binding and formation of malondialdehyde, but did not alter the lag time. These results suggest that the properties of voltage-dependent calcium channels are modified by conditions that promote lipid peroxidation.
Ebersole
B J
BJ
Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia.
Molinoff
P B
PB
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D046508:Culture Techniques; D004095:Dihydropyridines / Q000378:metabolism*; D007501:Iron / Q000494:pharmacology; D017275:Isradipine; D015227:Lipid Peroxidation / Q000187:drug effects*; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D008315:Malondialdehyde; D007501:Iron; D001205:Ascorbic Acid; D017275:Isradipine