Effects of N-chlorobenzyl analogues of amiloride on myocardial contractility, Na-Ca-exchange carrier and other cardiac enzymatic activities

Abstract

1. In electrically driven guinea pig left atria, micromolar concentrations (2 mumol/l to 80 mumol/l) of N-chlorobenzyl derivatives of amiloride (o-chlorobenzamil and 3',4'-dichlorobenzamil) produced quantitatively similar positive inotropic effects. Contracture developed with 3',4'-dichlorobenzamil. Endogenously released catecholamines contributed 30% to the positive inotropic effect of o-chlorobenzamil but did not contribute at all to the effect of 3',4'-dichlorobenzamil. When tested in the presence of the inhibitor of phosphodiesterase isobutylmethylxanthine, o-chlorobenzamil antagonized its positive inotropic effect, whereas 3',4'-dichlorobenzamil potentiated it. o-Chlorobenzamil also antagonized the positive inotropic effect of ouabain in that it shifted its concentration-effect curve to the right. Moreover, o-chlorobenzamil prevented the appearance of ouabain toxicity in terms of a rise in the resting force. 2. Also, in electrically driven guinea pig papillary muscle, micromolar concentrations (5 mumol/l to 30 mumol/l) of both N-chlorobenzyl derivatives of amiloride produced a positive inotropic effect. This effect was more marked with 3',4'-dichlorobenzamil than with o-chlorobenzamil and was associated for both compounds with lengthening of relaxation time. 3. o-Chlorobenzamil and 3',4'-dichlorobenzamil influenced, though not to the same extent, several systems involved in the onset and in the control of cardiac contractility. 3',4'-Dichlorobenzamil inhibited with the same potency Na-K-ATPase, sarcotubular Ca-ATPase, Na-Ca-exchange carrier, cAMP-dependent phosphodiesterase isolated from bovine heart and oxidative phosphorylation of mitochondria isolated from rat liver. Low micromolar concentrations of o-chlorobenzamil mainly inhibited Na-Ca-exchange carrier and cAMP-dependent phosphodiesterase.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride Derivatives as Blockers of Na+/Ca2+ Exchange: Effects on Mechanical and Electrical Function of Guinea‐Pig Myocardium

“…We have presented evidence that the amiloride derivatives BB, DCB, DBDB inhibit membrane currents in cardiac myocytes at concentrations in the same range as or lower than reported for half maximum inhibition of Na+/Ca2+ exchange in pituitary plasma membrane vesicles (Kaczorowski et al 1985). All 3 compounds clearly inhibited Ica (L-type calcium channels) which confirms results reported by other groups in a variety of different cell types (Bielefeld et al 1986, Garcia et al 1990. The amiloride derivatives also inhibited cardiac INa, as might have been expected from previous data on block of Na+ channels in frog skin (Cuthbert & Fanelli 1978) or reduction of dV/df,, in canine cardiac tissue (Marchese et al 1985, Satoh & Hashimoto 1986.…”

“…Furthermore, force of contraction could be modulated by effects of the amiloride derivatives on various enzymatic activities. For example, DCB was reported to impair the function (Nat +K+)-ATPase, Ca2+-ATPase of the sarcoplasmic reticulum, CAMP-dependent phosphodiesterase and mitochondria1 oxydative phosphorylation (Siegl et al 1984, Floreani et al 1987. However, these effects were not investigated in our present study.…”

“…All three drugs also impair Na+/ H + exchange (Vigne et al 1984) and various membrane conductances (e.g. Bielefeld et al 1986, Garcia et al 1990, Nasri-Sebdani et al 1989, Tang et al 1988, the impact of these effects on force of contraction are discussed below. Furthermore, force of contraction could be modulated by effects of the amiloride derivatives on various enzymatic activities.…”

“…1984;Slaughter et al 1988; for review, see Ravens & Wettwer 1989). In multicellular cardiac preparations, both positive and negative inotropic effects of amiloride and its derivatives have been reported: positive inotropic effect of amiloride in guinea-pig right atria (Pousti & Khoyi 1979;Floreani & Luciani 1984), positive inotropic effect of 3',4'-dichlorobenzamil in guinea-pig left atria and papillary muscle (Floreani et al 1987), negative inotropic effect 3',4-* To whom correspondence should be directed. dichlorobenzamil in guinea-pig papillary muscle (Siegl et al 1984), positive inotropic effect of amiloride in guinea-pig left atria, no effect in rat left atria (Cargnelli et al 1989).…”

3,4 Dichlorobenzamil‐sensitive, monovalent cation channel induced by palytoxin in cultured aortic myocytes

“…3,4 DCB has been reported to inhibit a variety of membrane ion transport processes such as the Na+/Ca2" exchanger (Siegl et al, 1984;Kaczorowski et al, 1985;Floreani et al, 1987;Vigne et al, 1988), L-type Ca2" channels (Garcia et al, 1990), and the (Na+,K+) ATPase (Floreani et al, 1987). The IC50 values for 3,4 DCB inhibition of the PTX-activated Na+ influx in aortic myocytes and in chick cardiomyocytes (8-10 -OM) are similar to the IC50 values reported for 3,4 DCB inhibition of the Na+/Ca2+ exchanger in neuronal cells (Kaczorowski et al, 1985), in cardiac cells (Siegl et al, 1984;Floreani et al, 1987), and in aortic myocytes (Vigne et al, 1988). Since PTX is known to induce a rise in the intracellular Ca2" concentration ([Ca2+]i) in cardiomyocytes (Frelin et al, 1990a), we previously proposed that the 3,4 DCB sensitive 22Na' uptake activated by PTX could result from an increased activity of the Na+/Ca2+ exchange system consecutive to a primary rise in [Ca2+]i.…”