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Published on: February 10, 2011
Outwardly rectifying currents in guinea pig outer hair cells
A P Nenov1, C Norris, R P Bobbin
1Kresge Hearing Research Laboratory of the South, Department of Otorhinolaryngology and Biocommunication, Louisiana State University Medical Center, New Orleans 70112-2234, USA.
This study investigated potassium (K+) currents in outer hair cells (OHCs), finding evidence for two distinct channel types. One resembles big-conductance Ca2+-dependent K+ (BK) channels, while the other acts like a delayed rectifier channel.
Area of Science:
- Cellular Electrophysiology
- Auditory Neuroscience
- Ion Channel Physiology
Background:
- Outwardly rectifying currents in hair cells are partially carried by big-conductance Ca2+-dependent K+ (BK) channels.
- Previous research suggested a separate voltage-dependent, Ca2+-independent K+ channel contributes to these currents in guinea pig outer hair cells (OHCs).
Purpose of the Study:
- To test the hypothesis that outwardly rectifying currents in OHCs comprise two separable current components.
- To characterize the voltage dependence and sensitivity of these currents to specific channel blockers.
Main Methods:
- Patch clamp techniques were employed on OHCs.
- The effects of external Ca2+ reduction, charybdotoxin (ChTx), Cd2+, and 4-aminopyridine (4-AP) on currents were analyzed.
- Voltage dependence and sensitivity to blockers were assessed.
Main Results:
- Lowering external Ca2+ did not alter the currents.
- Charybdotoxin (ChTx) and Cd2+ each blocked approximately 50% of the currents, causing a depolarizing shift and decreased voltage sensitivity.
- 4-Aminopyridine (4-AP) also blocked about 50% of the currents, but induced a hyperpolarizing shift and increased voltage sensitivity.
- Currents were more sensitive to 4-AP block at +40 mV than at -20 mV.
- Longer OHCs exhibited larger outwardly rectifying currents than shorter OHCs.
Conclusions:
- The findings support the existence of two distinct outwardly rectifying K+ channel types in OHCs.
- One channel type appears similar to BK channels, while the other resembles delayed rectifier K+ channels.
- Cell length correlates with the magnitude of outwardly rectifying currents in OHCs.
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