Voltage- and Patch-Clamp Experiments in
Virtual Computer Laboratories (cLABs-Neuron).
Hans A. Braun; Horst Schneider; Bastian Wollweber;
Heiko B. Braun & Karlheinz Voigt
Institute of Physiology, Deutschhausstr. 2, 35037 Marburg, Germany
Introduction
• „cLABs“ is a series of multimedial programs for teaching
dynamic biological and physiological mechanisms in an
interactive and virtual environment which allows users to
perform their own sets of experiments.
• cLABs programs are equally suitable for universities
and biology classes at schools as well as for private studies.
• “cLABs-Neuron”, our latest cLABs-Software, demonstrates the interrelations between ion channel dynamics and
membrane currents and voltages. It consists of the modules:
I. Membrane Properties
II. Ion Channels
III. Voltage-/Current-Clamp Experiments
Available from:
Sheffield BioScience Programs
Flat 1 Salisbury Heights
31 Salisbury Road
Edinburgh EH16 5AA, UK
Tel: + 4 131 662 8225
E-mail: d.dewhurst@ed.ac.uk
Price: €490 £310 (Institutional, multi-user licence)
I. Membrane Properties
This module provides animations and simulations to basic
functions of neuronal membrane properties which are
described in terms of their electrical equivalents.
Electrical Equivalents
Illustrates the functional
membrane properties (=
bilipid layer and ion
channels) and their electrical
equivalents (= membrane
capacitance and resistance).
RC-Circuit
(1)
supported by: BM&T Heidelberg/Marburg
DAQ-Solutions, Lohra, TransMIT, Giessen
(2)
(3)
(4)
(5)
Visualises current flows
and potential changes
across a resistor and a
capacitor in a RC-parallel
circuit.
Closing the circuit leads to a constant current flow which divides into a current via the capacitor and the resistor (1-2). At first the major current is flowing on the capacitor. The
more the capacitor is charged the more current is flowing through the resistor. When the circuit is opened (3-5), the capacitor discharges across the resistor.
RC-Lab
(1)
Allows experiments to examine the voltage changes that occur in
a RC-parallel circuit when current pulses are applied and no active
elements (e.g. ion channels) are involved.
• Resistance and capacitance of the RC-circuit can be changed
• A variable number of current pulses of pre-selectable
amplitude, duration and delay can be applied.
Conductance
This interactive section can be used to learn how the membrane potential
can be changed with alterations of ionic conductances. For an intuitive
understanding we use a simplified circuit which only consider the Na and K
currents and even neglect the membrane capacitance (stationary condition).
• You can move the sliders of the potentiometers to see how the membrane
potential and currents change as a function of the ionic conductances.
• The buttons allow pre-sets of the conductances to minimal, maximal or
equal values and also simulates the changes during an action potential.
(1) Superposition of the
potential changes during
stimulation with repetitive
current pulses.
(2) Effect of capacitance
changes on the membrane
potential after stimulation
by a constant current
pulse.
(2)
II. Ion Channels
(1)
(2)
(3)
The ion-channel module
embraces the structure,
gating mechanisms and
pharmacological sensitivity of voltage dependent
Na and K ion channels.
• The first part of the program introduces and describes the main characteristics of one- and two-gate ion
channels with a selectivity for potassium and sodium, respectively (1-2).
• A following interactive section simulates single channel Na- and K-currents. Here, the user can de- or
repolarize a virtual membrane and record the resulting ion currents, as well as watch the gating
mechanisms (3).
Single Channel Lab
(4)
(5)
This virtual laboratory is the main
part of the module and shows the
time course of Na- and K-currents,
according to the number of ion
channels in a virtual cell membrane.
(7)
(6)
The user can stimulate a certain
number of single Na- and K-ion
channels and the record the
respective currents, which are add
up to a virtual whole cell current (4).
• The Nernst reversal potential (Urev) is calculated from the setting of the inner and outer
Na- and K-ion concentration (5). Pharmacological effects can be tested by selection of
ion channel blockers, like TEA or TTX (5).
• Various stimulus pulse parameters can be set (6), e.g. to demonstrate that the direction of
the Na current is reversed above a certain command potential (Urev)(7).
III. Voltage-/Current-clamp Experiments
The third module provides a virtual lab for
voltage- and current-clamp experiments with
different types of neurones and also explains
background and concepts of the recording
techniques.
(1)
(2)
Recording Techniques
This interactive module shows step-by-step how the generation of actions potentials on current injection (1) leads to the concepts of current-recordings in a
voltage-clamp circuit (2). Recording and stimulating electrodes can be inserted into virtual neurons. Voltage- and current-clamp recordings during the
application of hyper- or depolarising stimuli of different amplitudes illustrate the transitions from purely passive to active neuron responses.
Voltage/Current-Clamp Lab
(1)
(2)
(3)
The Voltage/Current Clamp Lab:
a virtual computer laboratory for both currentand voltage-clamp experiments with mathematically simulated neurons (see recording
examples).
The simulations are based on simplified
Hodgkin-Huxley (HH) type algorithms.
A neuron editor (left) allows the user to change
the neuron’s parameters and to develop and
save his/her own favourite neurons.
Recording examples (1-3)
(1) Voltage-clamp recording which also
shows individual ionic conductance's and
currents.
(2) Passive response and action potentials,
one of them drastically lengthened because
of application of TEA.
(3) Impulse sequences recorded from a HHtype neuron which was converted into a
„pacemaker“ neuron with slight modifications of the activation curves.