BIPN140 Lecture 3 Outline - equilibrium potentials for ions...

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Lecture 3 September 30, 2010 BIPN140 Reading: Chapters 2 & 3 Ion Channels and Currents Ion Channels Four classes: resting (leak), voltage-dependent, ligand-dependent, sensory; subclasses for different ions; transport is passive In the whole cell, V m is determined by dominant class of channels; equivalent circuit Recording channel activity Whole cell recording of current (I; 1000's of channels) Single channel recording of current (i; 1 or several channels) Numbers of channels Numbers of ions that flow Ion concentration gradients are minimally affected; pumps sustain the gradients over the long term - transport is active Channel Properties Permeation - the ability of channels to pass ions a) Single channel conductance-record current at different potentials; from Ohm's law γ = i/V Range of values 5-400 pS b) Ion selectivity-from reversal potentials determined in (a); test by shifting
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Unformatted text preview: equilibrium potentials for ions involved Pharmacology – use of agents other than primary stimuli that alter either permeation properties c) Types of channels: K + , Ca ++ and Na + Kinetics – the gating (opening and closing) of channels a) leak channels flicker open and closed without stimuli 1 b) regulated channels have open probability dependent on stimuli c) observations; assessment of open probability (P open ) d) relationship of macroscopic currents and microscopic currents I = N . i . P open ; ensemble averages of single channel currents yield miniature versions of the whole cell current: benefit lies in knowing its single channel composition e) activation vs inactivation (voltage-dependent) or desensitization (ligand-dependent); representation by state diagrams for Kv and Na channels 2...
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