Non-selective Effects of Amiloride and Its Analogues on Ion Transport Systems and Their Cytotoxicities in Cardiac Myocytes

Abstract

ABSTRACT-The effects of amiloride and its analogues (3',4'-dichlorobenzamil (DCB), 2',4'-dimethylbenzamil (DMB), 5-(N-ethyl-N-isopropyl)amiloride (EIPA) and 5-(N-methyl-N-isobutyl)amiloride (MIBA)) on cardiac ion transporters (Na+/Ca2+ exchanger, Na+/H+ exchanger, Na+ pump and Ca 21 pump) and their cytotoxicities were tested in cardiac myocytes. All the tested compounds showed concentration-dependent inhibitory effects on the ion transporters studied in canine cardiac sarcolemmal vesicles. The concentrations (NM) of amiloride, DCB, DMB, EIPA and MIBA required to produce 50% inhibition were > 1000, 19, 10, 83 and 84, respectively, for the Na+/Ca2+ exchanger; 130, 73, 63, 16 and 14 for the Na+/H+ exchanger; > 1000, 72, > 300, > 300 and > 300 for the Na+ pump; and > 1000, 37, 93, 90 and 70 for the Ca 21 pump, respectively. Furthermore, these agents induced cell death in isolated rat cardiac myocytes and the 50% lethal concentrations (,uM) were > 1000, 9.2, 30, 16 and 17, respectively. These findings demonstrate that amiloride and its analogues have non-selective inhibitory effects on cardiac ion transporters and cytotoxicity in cardiomyocytes. When these drugs are employed as experimental tools to investigate the involvement of ion transporters in cell functions, the results must be interpreted with caution.

Pharmacology of Brain Na+/Ca2+Exchanger: From Molecular Biology to Therapeutic Perspectives

“…The synthesis of amiloride and amiloride analogs as K ϩ -sparing diuretics capable of inhibiting kidney epithelial Na ϩ -channels was first described by Cragoe et al (1967). Subsequently, these compounds were shown to inhibit other ion transport processes such as NCX, Na ϩ /H ϩ exchanger, and VGCC (Murata et al, 1995). Since then, in an attempt to evaluate NCX activity, amiloride has been used as a probe to block NCX function (Sharikabad et al, 1997).…”

Localization and Functional Relevance of System A Neutral Amino Acid Transporters in Cultured Hippocampal Neurons

“…As system A carriers transport MeAIB by symporting Na ϩ ions (18, 21), we investigated whether the increase in mEPSC frequency could be produced by a cytosolic calcium increase consequent to the extrusion of Na ϩ ions mediated by the Na ϩ /Ca 2ϩ exchanger as described previously (33). To address this point, mEPSC frequency and amplitude were measured upon MeAIB treatment in neuronal cultures exposed to 35 M dimethylbenzamil, a blocker with a relatively high affinity for the Na ϩ /Ca 2ϩ exchanger (33,34). Dimethylbenzamil was incubated in the bath 10 -15 min before MeAIB application.…”

A novel antagonist, No. 7943, of the Na+/Ca2+ exchange current in guinea‐pig cardiac ventricular cells

“…Synthetic compounds reported as Na+/Ca2+ exchange inhibitors are amiloride derivatives (Kaczorowski et al, 1985;Kleyman & Cragoe, 1988). Among them, DCB (3',4'-dichlorobenzamil) has been demonstrated to inhibit the Na+/ Ca2+ exchanger in cardiac membrane vesicles with a relatively low IC50 value of 17-30 giM (Siegl et al, 1984;Kaczorowski et al, 1985;Kleyman & Cragoe, 1988;Murata et al, 1995). DCB, however, also inhibits the voltage-gated Na+ channel (Kleyman & Cragoe, 1988) and T-type and L-type Ca2" channels even more potently than the Na+/Ca2+ exchange current in pituitary cells (Suarez-Kurtz & Kaczorowski, 1988).…”