Selectivity of inhibition of Na(+)-Ca2+ exchange of heart mitochondria by benzothiazepine CGP-37157.
The objective was to determine if the benzothiazepine compound CGP-37157 selectively inhibits the Na(+)-Ca2+ exchanger of cardiac mitochondria without affecting the L-type voltage-dependent calcium channel, the Na(+)-Ca2+ exchanger, or the Na(+)-K(+)-ATPase of the cardiac sarcolemma, or the Ca(2+)-ATPase of the cardiac sarcoplasmic reticulum. Mitochondrial Na(+)-Ca2+ exchange activity was determined by monitoring intramitochondrial free [Ca2+] in isolated heart mitochondria loaded with the Ca(2+)-sensitive fluorophore fura-2. CGP-37157 inhibited the activity of mitochondrial Na(+)-Ca2+ exchange in a dose-dependent manner (IC50 0.36 microM). Calcium currents were recorded by whole-cell voltage clamp in isolated neonatal ventricular myocytes. Diltiazem was able to block the recorded current completely, thus confirming the current to be exclusively L-type. CGP-37157 had no effect on the calcium current recorded under identical conditions. CGP-37157, at concentrations < or = 10 microM, had no effect on the activities of the Na(+)-Ca2+ exchanger and Na(+)-K(+)-ATPase in isolated cardiac sarcolemmal vesicles or on activity of the Ca(2+)-ATPase in isolated cardiac sarcoplasmic reticulum vesicles. The data suggest that CGP-37157 is a potent, selective, and specific inhibitor of mitochondrial Na(+)-Ca2+ exchange at concentrations < or = 10 microM.
Cox
D A
DA
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, OH 45267-0575.
Conforti
L
L
Sperelakis
N
N
Matlib
M A
MA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002998:Clonazepam / Q000031:analogs & derivatives* / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013841:Thiazepines / Q000494:pharmacology*
D013841:Thiazepines; D002998:Clonazepam; C079032:CGP 37157; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D004110:Diltiazem; D002118:Calcium