Effect of diltiazem on the release of calcium from the canine fragmented cardiac sarcoplasmic reticulum

Masato Hirata, Tetsuaki Inamitsu

Research output: Contribution to journalArticle

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Abstract

Fragmented sarcoplasmic reticulum fraction (SR) was prepared from the ventricle of canine heart, and the effect of diltiazem on its Ca2+ binding and Ca2+ release was examined by centrifugation and filtration methods using 45Ca. Cardiac SR bound 45-55 nmoles/mg of Ca ions in the presence of Mg-ATP. Diltiazem in concentrations up to 10-4 M had little effect on the Ca2+ binding of SR. The membrane of cardiac SR was “depolarized” by either changing propionate to chloride (anionic) or potassium to Tris (hydroxymethyl) aminomethane (Tris) (cationic). About 12% of the maximum Ca2+ bound to the S R was released by cationic “depolarization”, but no Ca2+ was released by anionic “depolarization”. The Ca2+ release induced by the cationic “depolarization” was inhibited by diltiazem, and the inhibitory effect of diltiazem on the Ca2+ release was dependent on the incubation time. Incubation of the SR with 3X10-6 M diltiazem for 30 sec almost completely inhibited the release of Ca2+, while incubation with 3x10-7 M diltiazem incompletely inhibited the Ca2+ release. About 20% of the maximum Ca2+ bound to the SR was released by the addition of 5.1 mM caffeine. The Ca2+ release induced by caffeine was inhibited by increasing the concentration of MgCI2 from 5 to 10 mM, but was not inhibited by 10 mM procaine. An increase of ATP concentration accelerated the time course of the caffeine-induced release of Ca2+ from the SR and subsequent rebinding of Ca2+. Diltiazem up to 10-5 M had no effect on the caffeine-induced Ca2+ release. These findings clearly indicate that diltiazem inhibits the “depolarization”-induced Ca2+ release from cardiac sarcoplasmic reticulum.

Original languageEnglish
Pages (from-to)991-997
Number of pages7
JournalThe Japanese Journal of Pharmacology
Volume33
Issue number5
DOIs
Publication statusPublished - Jan 1 1983

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Diltiazem
Sarcoplasmic Reticulum
Canidae
Calcium
Caffeine
Adenosine Triphosphate
Procaine
Tromethamine
Propionates
Centrifugation
Heart Ventricles
Chlorides
Potassium
Ions
Membranes

All Science Journal Classification (ASJC) codes

  • Pharmacology

Cite this

Effect of diltiazem on the release of calcium from the canine fragmented cardiac sarcoplasmic reticulum. / Hirata, Masato; Inamitsu, Tetsuaki.

In: The Japanese Journal of Pharmacology, Vol. 33, No. 5, 01.01.1983, p. 991-997.

Research output: Contribution to journalArticle

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abstract = "Fragmented sarcoplasmic reticulum fraction (SR) was prepared from the ventricle of canine heart, and the effect of diltiazem on its Ca2+ binding and Ca2+ release was examined by centrifugation and filtration methods using 45Ca. Cardiac SR bound 45-55 nmoles/mg of Ca ions in the presence of Mg-ATP. Diltiazem in concentrations up to 10-4 M had little effect on the Ca2+ binding of SR. The membrane of cardiac SR was “depolarized” by either changing propionate to chloride (anionic) or potassium to Tris (hydroxymethyl) aminomethane (Tris) (cationic). About 12{\%} of the maximum Ca2+ bound to the S R was released by cationic “depolarization”, but no Ca2+ was released by anionic “depolarization”. The Ca2+ release induced by the cationic “depolarization” was inhibited by diltiazem, and the inhibitory effect of diltiazem on the Ca2+ release was dependent on the incubation time. Incubation of the SR with 3X10-6 M diltiazem for 30 sec almost completely inhibited the release of Ca2+, while incubation with 3x10-7 M diltiazem incompletely inhibited the Ca2+ release. About 20{\%} of the maximum Ca2+ bound to the SR was released by the addition of 5.1 mM caffeine. The Ca2+ release induced by caffeine was inhibited by increasing the concentration of MgCI2 from 5 to 10 mM, but was not inhibited by 10 mM procaine. An increase of ATP concentration accelerated the time course of the caffeine-induced release of Ca2+ from the SR and subsequent rebinding of Ca2+. Diltiazem up to 10-5 M had no effect on the caffeine-induced Ca2+ release. These findings clearly indicate that diltiazem inhibits the “depolarization”-induced Ca2+ release from cardiac sarcoplasmic reticulum.",
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