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Membrane currents elicited by divalent cations in Xenopus oocytes
R Miledi1, I Parker, R M Woodward
1Department of Psychobiology, University of California, Irvine 92717.
The Journal of Physiology
|October 1, 1989
Summary
Divalent cations like cobalt can trigger oscillatory membrane currents in Xenopus oocytes by increasing intracellular calcium, activating chloride channels. This response is specific to certain cations and occurs within the oocyte membrane itself.
Area of Science:
- Cellular electrophysiology
- Ion channel function
- Xenopus oocyte models
Background:
- Xenopus oocytes are widely used models for studying ion transport and signaling pathways.
- Divalent cations are known to influence cellular processes, but their specific effects on oocyte membrane currents are not fully characterized.
Purpose of the Study:
- To investigate the effects of various divalent cations on membrane currents in Xenopus oocytes.
- To elucidate the mechanisms underlying cation-induced oscillatory currents and identify the ion channels involved.
Main Methods:
- Voltage-clamp recordings from Xenopus oocytes.
- Application of various divalent cations (Co2+, Cd2+, Ni2+, Zn2+, Mn2+, Cr2+, Sr2+, Ba2+, Ca2+, Mg2+) to the bath.
- Intraoocyte injection of inositol 1,4,5-trisphosphate (IP3) and chelators (EGTA).
- Defolliculation of oocytes to confirm membrane localization of responses.
Main Results:
- Cobalt ions (Co2+) evoked slow, oscillatory membrane currents in a subset of oocytes, with sensitivity varying between frogs.
- Other divalent cations (Cd2+, Ni2+, Zn2+, Mn2+, Cr2+) also elicited oscillations, while Sr2+, Ba2+, Ca2+, and Mg2+ showed minimal activity.
- Oscillatory currents were dependent on intracellular calcium and mimicked by IP3 injection, indicating activation of Ca2+-gated Cl- channels.
- Divalent cations also induced smaller, smooth currents with varying ionic bases and sensitivities, including a Zn2+-specific K+ current.
Conclusions:
- Extracellular divalent cations interact with the oocyte surface to increase intracellular inositol phosphates, leading to calcium release and activation of Ca2+-gated Cl- channels.
- The observed responses are intrinsic to the oocyte membrane and not dependent on follicular cells.
- Divalent cations can modulate distinct ion transport pathways, including oscillatory Cl- currents and smooth K+ currents, with frog-specific variations.