Isolation of A-type K+ current in hair cells of the frog crista ampullaris.
Different procedures to isolate the K+ A-type current (IA) from other membrane currents were tested on the complex inactivating outward K+ current generated in hair cells from the peripheral regions of the frog crista ampullaris. Experiments were performed in thin slices of epithelium using the whole-cell configuration of the patch-clamp technique. The conventional conditioning voltage protocol did not allow a satisfactory isolation of IA, due to the presence of other K+ currents showing overlapping steady-state inactivation properties. An attempt to block other K+ currents using calcium-free saline containing 50 mM TEA also failed to provide a satisfactory isolation of IA, due to contamination by a residual sustained current, probably consisting of a slow delayed outward K+ current (IK). Use of the selective A-channel blocker 4-aminopyridine (4-AP) at concentrations < 12 mM was also unsatisfactory because at these concentrations 4-AP produced a voltage-dependent blockade. Conversely, use of 4-AP at concentrations of 15-20 mM allowed a good separation of an uncontaminated IA. These results indicate that IA in hair cells of vestibular epithelium can be isolated most effectively by the 4-AP procedure, provided that sufficiently high concentrations of the A-channel blocker are used.
Russo
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G
Institute of General Physiology, University of Pavia, Italy.
Masetto
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S
Prigioni
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I
D000818:Animals; D004594:Electrophysiology; D005071:Evoked Potentials / Q000502:physiology; D018069:Hair Cells, Vestibular / Q000737:chemistry / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods*; D015221:Potassium Channels / Q000502:physiology*; D011893:Rana esculenta
D015221:Potassium Channels