Rocchetti M, Besana A, Mostacciuolo G, Micheletti R, Ferrari P, Sarkozi S, Szegedi C, Jona I, Zaza A. Modulation of Sarcoplasmic Reticulum Function by Na+/K+Pump Inhibitors with Different Toxicity: Digoxin and PST2744 [(E,Z)-3-((2-Aminoethoxy)imino)androstane-6,17-dione Hydrochloride].
J Pharmacol Exp Ther 2004;
313:207-15. [PMID:
15576469 DOI:
10.1124/jpet.104.077933]
[Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
OBJECTIVE
To gain some insight on the lesser arrhythmogenic properties of PST2744 [(E,Z)-3-((2-aminoethoxy)imino)androstane-6,17-dione hydrochloride] compared with digoxin, we compared modulation of intracellular Ca2+ dynamics by the two agents.
METHODS
SERCA (sarcoplasmic reticulum Ca2+-ATPase) activity and Ca2+ leak rate were measured in sarcoplasmic reticulum (SR) vesicles from guinea pig ventricles. Membrane current, intracellular Ca2+, and twitch amplitude were evaluated in guinea pig ventricular myocytes with or without blockade of the Na+/Ca2+ exchanger.
RESULTS
In SR vesicles, PST2744 (30-300 nM), but not digoxin, increased SERCA activity; digoxin only (> or =0.1 nM) increased SR Ca2+ leak. In myocytes with blocked Na+/Ca2+ exchanger, Ca2+ reloading of caffeine-depleted SR was enhanced by PST2744 and slightly inhibited by digoxin. In myocytes with functioning Na+/Ca2+ exchanger, both agents increased diastolic Ca2+, SR Ca2+ content, the gain of Ca2+-induced Ca2+ release, the rate of cytosolic Ca2+ decay, twitch amplitude, and relaxation rate. Consistent with the observations in SR vesicles, the effects on SR Ca2+ content and Ca2+ decay rate were significantly larger for PST2744 than for digoxin.
CONCLUSIONS
In isolated SR vesicles, PST2744 and digoxin directly affected SR function in opposite ways; this could be reproduced in myocytes during Na+/Ca2+ exchanger blockade. Under physiological conditions (functioning Na+/Ca2+ exchanger), the two agents affected Ca2+ dynamics in the same direction, as expected by their Na+/K+ pump inhibition; however, differential SR modulation was still expressed by quantitative differences. Thus, the more favorable inotropy-to-toxicity ratio previously described for PST2744 appears to be associated with direct SERCA stimulation and/or lack of enhancement of Ca2+ leak.
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