Effects of cationic substitutions on delayed rectifier current in type I vestibular hair cells.
The resting potassium current (I(KI)) in gerbil dissociated type I vestibular hair cells has been characterized under various ionic conditions in whole cell voltage-clamp. When all K(+) in the patch electrode solution was replaced with Na(+), (Na(+))(in) or Cs(+), (Cs(+))(in), large inward currents were evoked in response to voltage steps between -90 and -50 mV. Activation of these currents could be described by a Hodgkin-Huxley-type kinetic scheme, the order of best fit increasing with depolarization. Above approximately -40 mV currents became outward and inactivated with a monoexponential time course. Membrane resistance was inversely correlated with external K(+) concentration. With (Na(+))(in), currents were eliminated when K(+) was removed from the external solution or following extracellular perfusion of 4-aminopyridine, indicating that currents flowed through I(KI) channels. Also, reduction of K(+) entry through manipulation of membrane potential reduced the magnitude of the outward current. Under symmetrical Cs(+), 0 K(+) conditions I(KI) is highly permeable to Cs(+). However, inward currents were reduced when small amounts of external K(+) were added. Higher concentrations of K(+) resulted in larger currents indicating an anomalous mole fraction effect in mixtures of external Cs(+) and K(+).
Rennie
K J
KJ
Department of Otolaryngology, The University of Texas Medical Branch, Galveston, Texas 77555, USA.
Correia
M J
MJ
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002412:Cations / Q000494:pharmacology*; D002586:Cesium / Q000494:pharmacology; D004553:Electric Conductivity; D005849:Gerbillinae; D018069:Hair Cells, Vestibular / Q000187:drug effects / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
D002412:Cations; D007473:Ion Channels; D002586:Cesium; D012964:Sodium; D015761:4-Aminopyridine; D011188:Potassium