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Electrical transients produced by the toad bladder in response to altered serosal composition at constant osmolality
1Department of Physiology, University of Otago Medical School, Dunedin, New Zealand.
Biochimica Et Biophysica Acta
|July 8, 1992
Summary
Changes in serosal fluid ion concentrations, specifically potassium (K+) and chloride (Cl-), transiently altered toad urinary bladder electrical current. These findings suggest secondary active transport influences sodium (Na+) conductance.
Area of Science:
- Physiology
- Renal Physiology
- Ion Transport
Background:
- The toad urinary bladder is a model system for studying epithelial transport.
- Understanding ion transport mechanisms is crucial for renal function.
Purpose of the Study:
- To investigate the effects of altering serosal ionic composition on toad urinary bladder transepithelial current.
- To elucidate the role of secondary active transport and apical sodium (Na+) conductance.
Main Methods:
- Voltage-clamped toad urinary bladder preparation.
- Step-changes in serosal fluid potassium (K+) and chloride (Cl-) concentrations.
- Monitoring of transepithelial current.
- Isoosmotic and osmotic challenge experiments.
Main Results:
- A decrease in serosal K+ concentration (4 to 3 mmol/l) caused a transient increase in transepithelial current, peaking at 3 minutes.
- Reverse step in K+ concentration (3 to 4 mmol/l) elicited a smaller current response.
- Partial replacement of serosal Cl- with gluconate also induced a transient current increase.
- Biphasic current responses suggest involvement of both active transport and osmotic effects.
Conclusions:
- Secondary active transport likely enhances apical Na+ conductance in the toad urinary bladder.
- Osmotic effects contribute to the later phases of observed current responses.
- Ionic and osmotic gradients in the serosal medium significantly impact epithelial transport characteristics.