Ionic and Charge Movement Currents in a Sunfish Skeletal Muscle (Membrane Structure, Temperature, E-C Coupling)
Klein, Michael Gene
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https://hdl.handle.net/2142/71444
Description
Title
Ionic and Charge Movement Currents in a Sunfish Skeletal Muscle (Membrane Structure, Temperature, E-C Coupling)
Author(s)
Klein, Michael Gene
Issue Date
1986
Department of Study
Physiology and Biophysics
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Abstract
Electrical properties of striated muscle in a sunfish, Lepomis cyanellus, have been examined using a three microelectrode volt- age clamp method. The preparation was bathed in Ringer solutions designed to suppress unwanted currents and mechanical activity.
The ionic currents underlying the action potential consist of a rapidly activating inward current carried by Na('+), a delayed outward current carried by K('+) and a slower outward K('+) current. These cur- rents were fitted to a Hodgkin-Huxley (1952) formalism to quantitate the voltage- and time-dependence of the ionic permeabilities. The Na('+) current was fitted to m('3)h, where the m parameter describes activation and h accounts for spontaneous inactivation. The delayed K('+) current was fitted to n('4) kinetics and the slower K('+) current to s('1) kinetics.
The temperature dependence of activation rate constants for m, n and h were examined in sunfish acclimated to 25 and 7 C. The Arrhenius activation energy of m and h was constant over the range of temperatures examined (0 - 12 C), and was similar in both acclima- tion groups. The rate constant of n,(alpha)(,n), was linear with temperature (0 - 20 C) in cold-adapted sunfish, but exhibited a discontinuity, or "break-point" at 8 C in the relationship of warm adapted fibres such that the K('+) current kinetics were significantly slowed below this tem- perature. The thermal behavior of the K('+) conductance (gK('+)) was identical to the behavior of (alpha)(,n). Various alcohols, alkanes and deter- gents were ineffective in repriming the K('+) current, leaving open the question of a role for membrane lipids in modulating the K('+) current.
Membrane charge movement currents are small capacitative currents which exhibit complicated kinetics in the ON transient, containing apparently two species called Q(,(beta)) and Q(,(gamma)). The steady- state voltage dependence of charge movement (Q - V) is described by a Boltzman distribution with three parameters defining the rela- tionship. In sunfish fibres these are Q(,max) = 29.8 nC uF('-1), V' = -42.9 mV and k = 8.0 mV.
Low temperature paralyzes warm-adapted sunfish fibres. Charge movements in cold-immobilized fibres contain only a single compo- nent of charge. Q(,(beta)) - Q(,(gamma)) is apparently immobilized. The Q - V rela- tionship is described by Q(,max) = 17.9 nC uF('-1), V' = -33.1 mV and k = 16.0 mV. These results support the notion that Q(,(gamma)) is associated with release of Ca('++) from the sarcoplasmic reticulum, and that immobilization of Q(,(gamma)) blocks the Ca('++) release.
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