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0:00
Hello, my name is David Brown.
I'm a professor of pharmacology,
Department of Neuroscience, Physiology,
and Pharmacology at
University College London.
I'm going to talk to you
about the-M current and
its role in neuronal physiology.
0:14
What is the M-current?
It's a species of voltage-gated
potassium current.
It was first seen in frog neurons,
but is present in many mammalian and
human peripheral and central neurons,
and in the nerve fibres.
It is inhibited by stimulating
muscarinic acetylcholine receptors,
that's how it got its name 'M',
though in fact it can be inhibited by
stimulating other receptors so long as
they're linked to the G-protein, Gq.
Channels are composed of subunits of
the Kv7 family, mainly Kv7.2 and 7.3.
The function is to stabilise membrane
potential and to control excitability, so
that when the current is inhibited,
neurons are depolarised and
they show an increased excitability.
In this talk, I'll illustrate these
points with some pictures of experimental
recordings, just to give you a feel for
how the current works, and
how it affects nerve cell behavior.
1:09
This shows one of our original recordings
of the M-current in a frog sympathetic
neuron, made using a dual
electro-voltage clamp.
One electrode sets the voltage, and the
other one monitors the membrane current.
In the record on the right,
the cell membrane potential is held at -60
millivolts to start with, and then it's
set for one second to -30 millivolts.
This generates the outward
current shown by the arrow.
It has two main features, firstly,
it activates rather slowly over tens or
hundreds of milliseconds.
Secondly, it does not show the
inactivation characteristic of many other
voltage-gated potassium currents, as,
once switched on, the current stays on for
many seconds or minutes,
generating a steady outward current.
