Amiloride and diltiazem inhibition of microsomal and mitochondrial Na+ and Ca2+ transport

Abstract

Amiloride, a K+-sparing diuretic, and diltiazem, a Ca2+ channel antagonist, have both been reported to inhibit Na+ transport-associated processes in different subcellular membrane systems. In this report, similar inhibitory effects of both agents are demonstrated on Na+-induced Ca2+ release from rabbit heart mitochondria and on Na+ uptake in a kidney medulla microsomal preparation. Both amiloride and diltiazem produce 50% inhibition of Na+ uptake in kidney microsomes at the same concentrations. Heart mitochondrial Na+-induced Ca2+ release was 50% inhibited by 6 microM diltiazem and 200 microM amiloride. No effects of either agent on mitochondrial respiratory activity were observed. The results suggest a specific effect of both drugs on a Na+-binding site associated with an antiport exchange process. These data also extend previous observations suggesting the use of these agents as tools to define further ion transport mechanisms in biological membranes.

Mitochondrial Transport of Cations: Channels, Exchangers, and Permeability Transition

“…This pathway, the "Na ϩ -dependent pathway for Ca 2ϩ efflux" (NCE), has likewise been the subject of a large number of studies (e.g., Refs. 8,9,22,74,75,93,135,136,[159][160][161]164,182,283,296,303,308,318,363) and of a recent debate about the Na ϩ -Ca 2ϩ stoichiometry (23,180,361). The two pathways are distinct, since their kinetics are completely different, in that NICE is second order whereas NCE is first order in [Ca 2ϩ ] (360, 361).…”

“…The dependence on Na ϩ is sigmoidal, with typical K m values centered at ϳ8 -10 mM Na ϩ , and Na ϩ can be substitued by Li ϩ (85). Ca 2ϩ efflux is inhibited by Sr 2ϩ (303), Ba 2ϩ (207,208), Mg 2ϩ (361), Mn 2ϩ (135), and by a variety of compounds of pharmacological interest such as amiloride (182,308,318), trifluoperazine (160), diltiazem (74,75,283), verapamil (363), clonazepam, and bepridil (74), whereas it is stimulated by short-chain alcohols (296). A prominent modulatory effect by matrix pH has been reported, with a sharp optimum at pH 7.6 (22), and NCE is stimulated by treatment with glucagon and ␤-adrenergic agonists (136).…”

Calcium Antagonism—with Special Reference to Diltiazem

“…If this rise in intracellular calcium concentration could be prevented or delayed, myocardial tissue might be preserved. Diltiazem has been shown to decrease sodium and inorganic phosphate-induced transmembrane calcium fluxes in isolated rabbit mitochondria (30).…”

The Effect of Amiloride on the Cardiac Chronotropic Responses to Isoproterenol in Myocardial Aggregate Cells in Culture

“…Amiloride, however, should be stable for the duration of the experiment. Fourthly although changes in [Nali are proposed to be the mechanism of interaction of amiloride and isoproterenol the actual site of interaction could involve Na + exchange processes such as Na + -Ca2 + exchange which is weakly inhibited by amiloride (Sordahl et al 1984) or other processes. Amiloride interacts with guanine nucleotide regulatory proteins although it does not affect adenylate cyclase activity (Anand-Srivastava 1989).…”