Electrical and mechanical modulations by oxygen-derived free-radical generating systems in guinea-pig heart muscles
Abstract
The effects of free-radical generating systems and angiotensin-converting enzyme (ACE) inhibitors on the action potentials and contractile force in guinea-pig cardiac muscles were examined using conventional microelectrode and whole-cell voltage-clamp methods at 36 degrees C. Hydrogen peroxide (30-100 microM) prolonged 50%, 75% and 90% repolarization of action-potential duration (APD) approximately 15-25 min after its application. But the longer exposure reversed the APD shortening in a concentration-dependent manner. Other action-potential parameters were not altered to a significant extent. The contractile force was increased. Longer exposure inhibited the enhanced force (but it was still larger than control). The effects on the spontaneous action potential from right atrial muscle were almost the same. In whole-cell voltage-clamp experiments, H2O2 (100 microM) inhibited L-type Ca2+ current and enhanced delayed rectifier K+ current. The effects of light-activated rose bengal (10-100 nM) on the APD were similar to, but more potent than, those of H2O2. The response was observed rapidly after a light illumination. During exposure to rose bengal (100 nM), abnormal spontaneous action potentials or arrhythmias such as a bigeminy oc...Continue Reading
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