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Cationic amphiphiles prevent calcium leak induced by ATP depletion in myocardial cells
J R Clague1, J A Post, G A Langer
1Cardiovascular Research Laboratory, UCLA School of Medicine 90024-1760.
Abstract:
Excessive calcium influx is important in the irreversible injury of cardiac myocytes and other cell types. The mechanism is unknown, but possibilities include L-type channels, Na(+)-Ca2+ exchange, sarcolemmal (SL) defects, and calcium leak channels. In this study, metabolic inhibition was used to induce ATP depletion and augmented calcium influx in cultured cardiac myocytes. Inhibition of the L-type calcium channel and Na(+)-Ca2+ exchanger had no significant effect on the calcium leak. There was no significant lactate dehydrogenase release, indicating that the leak did not occur through major SL defects. No alterations in the asymmetric distribution of SL phospholipids were demonstrated. Phospholipid rearrangements were therefore not responsible. The leak was unaffected by 0.5 mM cadmium and 1 microM nifedipine but was augmented by 50 microM nifedipine, characteristics in common with calcium leak channels. Insertion of the cationic amphiphiles dodecyltrimethylammonium bromide or polymyxin B sulfate into the SL had a profound inhibitory effect on the calcium leak. The anionic amphiphile sodium dodecyl sulfate had the opposite effect, and the neutral amphiphile lauryl acetate had no effect. These results suggest that an alteration in the SL surface charge affects calcium leak. It is proposed that the augmented calcium influx occurs via calcium leak channels and that these can be modulated by charged amphiphiles.
Insights
Excessive calcium influx damages heart cells. This study reveals that calcium leak channels, not sarcolemmal defects, mediate this influx, and their activity is influenced by the cell membrane's surface charge.
Area of Science:
- Cardiology
- Cell Biology
- Biochemistry
Background:
- Excessive calcium influx contributes to irreversible cardiac myocyte injury.
- The precise mechanisms of this calcium influx, including potential roles for L-type channels, Na(+)-Ca2+ exchange, sarcolemmal defects, and calcium leak channels, remain incompletely understood.
Purpose of the Study:
- To investigate the mechanisms of augmented calcium influx in cultured cardiac myocytes induced by metabolic inhibition and ATP depletion.
- To determine the role of calcium leak channels in ATP-depletion-induced cardiac myocyte injury.
Main Methods:
- Metabolic inhibition was employed to induce ATP depletion and subsequent calcium influx in cultured cardiac myocytes.
- The effects of inhibiting L-type calcium channels and Na(+)-Ca2+ exchangers on calcium leak were assessed.
- The influence of various amphiphiles (cationic, anionic, neutral) on calcium leak was evaluated to probe sarcolemmal surface charge effects.
Main Results:
- Inhibition of L-type calcium channels and Na(+)-Ca2+ exchangers did not significantly affect calcium leak.
- No evidence of major sarcolemmal defects or phospholipid alterations was found.
- Calcium leak exhibited characteristics consistent with calcium leak channels, being modulated by nifedipine concentration and unaffected by cadmium.
- Cationic amphiphiles inhibited calcium leak, while anionic amphiphiles augmented it, suggesting a role for sarcolemmal surface charge.
Conclusions:
- Augmented calcium influx in metabolically inhibited cardiac myocytes occurs primarily via calcium leak channels.
- Sarcolemmal surface charge alterations significantly modulate the activity of these calcium leak channels.
- Charged amphiphiles can effectively modulate calcium leak, offering potential therapeutic targets for conditions involving excessive calcium influx.