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Voltage-dependent membrane capacitance in rat pituitary nerve terminals due to gating currents
1University of Colorado Medical School, Department of Medicine, Denver, Colorado 80262, USA.
Biophysical Journal
|February 27, 2001
Summary
Researchers detected sodium channel gating currents in pituitary nerve terminals using specialized equipment. These currents influence membrane capacitance, providing insights into nerve terminal function and sodium channel behavior.
Area of Science:
- Neuroscience
- Electrophysiology
- Molecular Biology
Background:
- Pituitary nerve terminals are crucial for hormone release.
- Voltage-gated sodium channels play a key role in nerve terminal excitability and secretion.
- Direct measurement of sodium channel gating currents in these terminals is challenging.
Purpose of the Study:
- To demonstrate and characterize sodium channel gating currents in single pituitary nerve terminals.
- To investigate the voltage and frequency dependence of these gating currents.
- To correlate gating current properties with ionic sodium currents.
Main Methods:
- Whole-terminal patch-clamp recordings from pituitary nerve terminals.
- Utilized a lock-in amplifier for sensitive detection of capacitance changes.
- Applied voltage steps and analyzed frequency dependence of membrane capacitance.
- Used pharmacological agents like dibucaine to probe channel function.
Main Results:
- Observed voltage-dependent membrane capacitance changes even when secretion and ionic currents were blocked.
- Identified a bell-shaped voltage dependence of capacitance, peaking around -40 mV, consistent with sodium channel gating.
- Found a strong correlation between voltage-dependent capacitance and sodium currents.
- Demonstrated that dibucaine reduced both sodium currents and voltage-dependent capacitance.
- Observed frequency dependence of capacitance matching sodium channel kinetics.
Conclusions:
- This study provides the first direct evidence of sodium channel gating currents in single pituitary nerve terminals.
- Voltage-dependent capacitance, measurable with lock-in amplification, reflects sodium channel gating.
- The properties of these gating currents align with the behavior of ionic sodium currents in these terminals.
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