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Properties of the Ca(2+)-activated Cl- current of Xenopus oocytes
E Centinaio1, E Bossi, A Peres
1peres@imiucca.csi.unimi.it
Abstract:
The properties of the Ca(2+)-activated Cl- current of Xenopus oocytes have been investigated by voltage-clamp and injections of D-3-deoxy-3-fluoro-myo-inositol 1,4,5-trisphosphate (3-F-lnsP3). Following 3-F-InsP3 injection, a transient phase of Ca(2+)-activated Cl- current occurred, caused by Ca2+ release from internal stores; subsequently, a secondary, long-lasting, current was recorded, signaling Ca2+ influx from the exterior (ICRAC). Changes in external Cl- during the sustained phase produced the expected shifts in reversal potential (Erev), while the conductance varied opposite to the predictions of simple electrodiffusional theory. Application of depolarizing pulses soon (10 s) after 3-F-InsP3 injection elicited membrane currents exhibiting a single exponential rise. During the sustained subsequent phase, the current elicited by depolarizations showed an early peak followed by a prominent decline. During the sustained phase, removal of calcium from the external solution, or its substitution with Ba2-, abolished voltage- and time-dependent components of the depolarization-induced current. Slope conductance analysis of the inactivating records revealed, in addition to the decline of the Ca(2+)-activated Cl- current, the presence of a second, inwardly directed current. This could be identified as a slowly inducible Na+ current already described in Xenopus oocytes.
Insights
This study investigated calcium-activated chloride currents in Xenopus oocytes using D-3-deoxy-3-fluoro-myo-inositol 1,4,5-trisphosphate (3-F-InsP3). Results revealed both calcium release and influx, with complex conductance changes and a secondary sodium current.
Area of Science:
- Cellular physiology
- Ion channel biophysics
- Xenopus oocyte electrophysiology
Background:
- Xenopus oocytes are a model system for studying ion channel function.
- Calcium-activated chloride currents play crucial roles in cellular signaling.
- Inositol trisphosphate receptors mediate calcium release from intracellular stores.
Purpose of the Study:
- To characterize the Ca(2+)-activated Cl- current in Xenopus oocytes.
- To investigate the role of intracellular calcium stores and influx in this current.
- To identify other ion currents activated during the process.
Main Methods:
- Voltage-clamp electrophysiology in Xenopus oocytes.
- Microinjection of D-3-deoxy-3-fluoro-myo-inositol 1,4,5-trisphosphate (3-F-InsP3).
- Manipulation of external ionic concentrations (Cl-, Ca2+, Ba2+).
Main Results:
- 3-F-InsP3 induced a transient Ca2+-activated Cl- current via internal Ca2+ release.
- A sustained current, indicative of Ca2+ influx (ICRAC), was observed.
- Voltage-clamp analysis revealed complex conductance changes and a secondary, slowly inducible Na+ current.
Conclusions:
- Xenopus oocytes exhibit complex Ca2+-activated Cl- current dynamics involving both Ca2+ release and influx.
- The current's properties deviate from simple electrodiffusion models.
- A secondary Na+ current co-exists with the Ca2+-activated Cl- current, suggesting coupled ionic events.