Effects of oxidants on the sarcoplasmic reticulum of saponin treated rat ventricular trabeculae

Abstract

Objective: The aim was to determine the effects of the superoxide anion, hydrogen peroxide, and hypochlorous acid on in situ cardiac sarcoplasmic reticulum.

Methods: Simultaneous measurement of caffeine induced calcium release from the sarcoplasmic reticulum and subsequent myofilament tension generation was made on saponin permeabilised rat ventricular trabeculae before, during, and after exposure to various reactive oxygen species. The superoxide anion (O2.-) was generated using the xanthine-xanthine oxidase system, hypochlorous acid (HOCl) was prepared from NaOCl, and hydrogen peroxide (H2O2) was added from a 30% stock solution.

Results: At [O2.-] sufficient to abolish tension generation by the myofilaments completely, the associated caffeine induced calcium release was unaffected. Both H2O2 and HOCl diminished caffeine induced calcium release but had differential effects on the associated tension response. Exposure to HOCl favoured the occurrence of spontaneous calcium releases from the sarcoplasmic reticulum.

Conclusions: The reactive oxygen species H2O2 and HOCl reduced the amount of calcium release from the sarcoplasmic reticulum while O2.- was without effect. In some preparations it was observed that HOCl favoured spontaneous calcium release which might additionally reduce the calcium content of the sarcoplasmic reticulum.