The Journal of Membrane Biology

, Volume 164, Issue 1, pp 11–24 | Cite as

Transmembrane Mg2+ Currents and Intracellular Free Mg2+ Concentration in Paramecium tetraurelia

  • R.R.  Preston


The properties of Mg2+ conductances in Paramecium tetraurelia were investigated under two-electrode voltage clamp. When bathed in physiological Mg2+ concentrations (0.5 mm), depolarizing steps from rest elicited a prominent Mg2+-specific current (I Mg) that has been noted previously. The dependence of this current on extracellular Mg2+ approximated that of Mg2+-induced backward swimming, demonstrating that I Mg contributes to normal membrane excitation and behavior in this ciliate. Closer analysis revealed that the Mg2+ current deactivated biphasically. While this might suggest the involvement of two Mg2+-specific pathways, both tail-current components were affected similarly by current-specific mutations and they had similar ion selectivities, suggesting a common pathway. In contrast, a Mg2+ current activated upon hyperpolarization could be separated into three components. The first, I Mg, had similar properties to the current activated upon depolarization. The second was a nonspecific divalent cation current (I NS) that was revealed following suppression of I Mg by eccentric mutation. The final current was relatively minor and was revealed following suppression of I Mg and I NS by obstinate A gene mutation. Reversal-potential analyses suggested that I Mg and I NS define two intracellular compartments that contain, respectively, low (0.4 mm) and high (8 mm) concentrations of Mg2+. Measurement of intracellular free Mg2+ using the fluorescent dye, Mag-fura-2, suggested that bulk [Mg2+] i rests at around 0.4 mm in Paramecium.

Key words:Paramecium— Mg2+ behavior — Mg2+ current — Mutation — Intracellular free Mg2+ homeostasis — Mag-fura-2 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Copyright information

© 1998 Springer-Verlag New York Inc.

Authors and Affiliations

  • R.R.  Preston
    • 1
  1. 1.Department of Physiology, Allegheny University of the Health Sciences, Philadelphia, PA 19129, USAUS

Personalised recommendations