Title

The transient potassium conductance of the somatic membrane of cultured embryonic rat neurons

Date of Award

1988

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Physiology and Biophysics

First Committee Member

Wolfgang Nonner, Committee Chair

Abstract

The transient K conductance of rat central neurons was studied under voltage clamp. Currents were recorded through tight-seal pipettes from whole neurons or 3-8 $\mu$m spheres of excised somatic membrane ('blebs'). Whole cells revealed a tetrodotoxin-sensitive Na current, followed by a K current that passed through a peak and was maintained at 60-90% of the peak during 300 ms. Somatic membrane isolated in the form of blebs also conducted Na and K currents, but the K current was mostly, and often exclusively, transient. This current was blocked by 4-aminopyridine (5 mM), but not affected by tetraethylammonium ion (1 mM).A transient K current was activated by depolarizations greater than $-$40 mV. Peak conductance increased in proportion to voltage with no indication of saturation up to +80 mV. Ensemble fluctuations suggested that less than 50% of the channels were open at the peak during a +40 mV depolarization. Steady-state inactivation was minimal after conditioning at $-$100 mV, and was complete at $-$50 to $-$30 mV. Recovery from inactivation followed a sigmoidal time course (half time ca. 50 ms at $-$90 mV, 25$\sp\circ$C).Substitution of external Na by K ion altered activation, but not inactivation. In high K, a given depolarization activated a larger and more rapidly rising conductance that could be saturated. Substitution of 1 mM external Mg by 1 mM Ca, or addition of 0.5 mM Cd, slowed activation.The gating characteristics of the transient K current varied significantly from neuron to neuron. Half times of inactivation, although constant and stable for a given neuron varied from 5 to 65 ms at 25$\sp\circ$C. Activation half-times ranged from 1 to 2 ms (+40 mV). The position on the voltage axis of peak conductance and steady-state inactivation curves varied over 30 mV. The degree of preceding inactivation did not affect the time course of the currents, suggesting channels of a given preparation were uniform in their inactivation properties.Possible kinetic models of the transient K channel gating are discussed. It appears that opening of these channels during activation involves a final reaction step that is weakly voltage dependent, and possibly ion dependent. The variability of the channel's gating properties is discussed in the context of mechanisms. (Abstract shortened with permission of author.)

Keywords

Biology, Neuroscience; Biophysics, Medical

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:8820794