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Anthracycline-induced inhibition of a calcium action potential in differentiated murine neuroblastoma cells
Abstract:
The effects of some anthracyclines on a Ca2+ -dependent action potential have been studied in differentiated murine neuroblastoma cells (N1E-115 clone). The differentiated neuroblastoma cell possesses characteristics of an electrically excitable cell and can generate propagated potential spikes in which Ca2+ is the inward charge carrier. This was shown by the fact that action potentials recorded from differentiated neuroblastoma cells in the presence of 10(-7) g of tetrodotoxin per ml, which inhibits active Na+ channels, had a spike amplitude that depended upon the extracellular Ca2+ concentration in a manner close to that predicted by the Nernst equation. The peak potential changed 28.9 mV/decade change in extracellular Ca2+. Local application to a cell of 10(-8) M doxorubicin produced inhibition of this Ca2+ -dependent action potential within 5 s of drug application and a maximum inhibition of 13% 60 s after drug application. There was almost complete recovery to the initial spike amplitude value within 10 min after removing drug. The same concentration of doxorubicin also produced complete inhibition, without recovery, of a Ca2+ -dependent after-discharge which followed the initial action potential in about half the cells studied. Increasing concentrations of doxorubicin produced dose-dependent inhibition of the initial Ca2+ -dependent action potential. Cells exposed to 10(-5) M doxorubicin showed 88% inhibition of the Ca2+ -dependent action potential with no recovery even 10 min after removing the drug. Daunomycin, 10(-6) M, produced 90% inhibition of the Ca2+ -dependent action potential. Daunomycin aglycone (10(-6) M), which lacks antitumor activity, had no significant effect on the Ca2+ -dependent action potential. The rapid onset of the drug-induced response together with the low concentrations of anthracyclines needed to inhibit voltage-dependent Ca2+ channels in the neuroblastoma cells suggest a direct effect of anthracyclines on the cell surface membrane. The findings are discussed in light of the possible role of Ca2+ in cancer cells.
Insights
Anthracyclines like doxorubicin and daunomycin inhibit calcium (Ca2+) dependent action potentials in neuroblastoma cells. This suggests a direct effect on cell membranes, potentially impacting calcium
Area of Science:
- Neuroscience
- Pharmacology
- Cell Biology
Background:
- Differentiated neuroblastoma cells exhibit electrical excitability.
- These cells generate action potentials where calcium (Ca2+) is the primary charge carrier.
- Tetrodotoxin-resistant action potentials confirm Ca2+ dependence.
Purpose of the Study:
- To investigate the effects of anthracyclines on Ca2+-dependent action potentials.
- To determine the mechanism and dose-dependency of anthracycline-induced inhibition.
- To explore the potential role of Ca2+ in cancer cells.
Main Methods:
- Electrophysiological recordings from differentiated murine neuroblastoma cells (N1E-115).
- Application of varying concentrations of doxorubicin and daunomycin.
- Assessment of action potential amplitude and recovery after drug removal.
Main Results:
- Doxorubicin (10(-8) M) rapidly inhibited Ca2+-dependent action potentials by up to 13%.
- Higher doxorubicin concentrations (10(-5) M) caused 88% inhibition with no recovery.
- Daunomycin (10(-6) M) induced 90% inhibition; daunomycin aglycone had no effect.
Conclusions:
- Anthracyclines directly inhibit voltage-dependent Ca2+ channels in neuroblastoma cells.
- Inhibition is rapid, dose-dependent, and suggests a cell membrane interaction.
- Findings highlight the role of Ca2+ in electrically excitable cancer cells.