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Reversible Ca gradients between the subplasmalemma and cytosol differentially activate Ca-dependent Cl currents
1Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322-3030, USA.
The Journal of General Physiology
|February 2, 1999
Summary
Calcium signals near the cell membrane, not in the bulk cytosol, activate calcium-activated chloride currents (ICaCl) in Xenopus oocytes. Localized calcium (Ca) gradients are crucial for understanding ICaCl activation.
Area of Science:
- Cellular physiology
- Ion channel function
- Calcium signaling
Background:
- Xenopus oocytes exhibit diverse calcium-activated chloride currents (ICaCl) with distinct properties.
- Understanding the relationship between calcium (Ca) signals and ICaCl activation is essential.
Purpose of the Study:
- To investigate how Ca signal amplitude and spatio-temporal characteristics influence the activation of different ICaCl.
- To differentiate the roles of Ca influx versus Ca release from internal stores in ICaCl activation.
Main Methods:
- Two-microelectrode voltage clamp to measure ICaCl.
- Confocal microscopy with Ca-sensitive fluorophores to measure intracellular Ca transients.
- Comparison of bulk cytosolic Ca indicators with membrane-targeted Ca indicators.
Main Results:
- Cytosolic Ca measurements poorly correlated with ICaCl, suggesting distinct Ca pools.
- Membrane-targeted Ca indicators showed strong correlation with ICaCl.
- Evidence for localized, transient Ca gradients at the subplasmalemmal space.
Conclusions:
- Subplasmalemmal Ca concentrations, not bulk cytosolic levels, are critical for ICaCl activation.
- Distinct Ca gradients form depending on the source of Ca (influx vs. release).
- Endoplasmic reticulum Ca sequestration influences bulk cytosolic Ca dynamics.