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A magnesium current in Paramecium
1Laboratory of Molecular Biology, University of Wisconsin-Madison 53706.
Abstract:
Recent reappraisals of the role of ionized magnesium in cell function suggest that many cells maintain intracellular free Mg2+ at low concentrations (0.1 to 0.7 mM) and that external agents can influence cell function via changes in intracellular Mg2+ concentration. Depolarization and hyperpolarization of voltage-clamped Paramecium elicited a Mg2(+)-specific current, IMg. Both Co2+ and Mn2+ were able to substitute for Mg2+ as charge carriers, but the resultant currents were reduced compared with Mg2+ currents. Intracellular free Mg2+ concentrations were estimated from the reversal potential of IMg to be about 0.39 mM. The IMg was inhibited when external Ca2+ was removed or a Ca2+ chelator was injected, suggesting that its activation was Ca2(+)-dependent.
Insights
This study reveals that magnesium ions (Mg2+) play a crucial role in cell function, with specific currents influenced by calcium. Intracellular Mg2+ levels were found to be critical for cellular processes.
Area of Science:
- Cellular Physiology
- Ion Transport Mechanisms
- Biophysics
Background:
- Recent research highlights the significance of ionized magnesium (Mg2+) in cellular functions.
- Cells may regulate intracellular free Mg2+ within a narrow range (0.1-0.7 mM).
- External factors can modulate cell activity by altering intracellular Mg2+ levels.
Purpose of the Study:
- To investigate the Mg2+-specific current (IMg) in voltage-clamped Paramecium.
- To determine the role of intracellular Mg2+ concentration in cellular responses.
- To explore the influence of external agents on IMg.
Main Methods:
- Utilized voltage-clamped Paramecium to elicit and measure ion currents.
- Employed cobalt (Co2+) and manganese (Mn2+) as substitute charge carriers for Mg2+.
- Estimated intracellular free Mg2+ concentrations using the reversal potential of IMg.
- Investigated the Ca2+-dependence of IMg by manipulating external Ca2+ levels and using Ca2+ chelators.
Main Results:
- A Mg2+-specific current (IMg) was observed during depolarization and hyperpolarization.
- Co2+ and Mn2+ could carry IMg, but with reduced current magnitudes compared to Mg2+.
- Estimated intracellular free Mg2+ concentration was approximately 0.39 mM.
- IMg activation was dependent on Ca2+, as evidenced by inhibition upon Ca2+ removal or chelation.
Conclusions:
- Intracellular free Mg2+ concentration is a critical determinant of cellular function in Paramecium.
- The Mg2+-specific current (IMg) is a Ca2+-dependent phenomenon.
- This study provides insights into the complex interplay between Mg2+, Ca2+, and cellular electrical activity.