Download ChannelProperties

Properties of voltage-gated channels to consider or determine
1) What is the reversal potential of the current that passes through the
channel? When a channel opens, it moves the voltage of the cell towards its
reversal potential. Decide whether the channel passes a “depolarizing
current”, which increases the voltage toward zero or above zero, or a
“hyperpolarizing current”, which decreases the voltage below its negative
resting value.
2) Does the channel pass a persistent current with no inactivation, or does it
have inactivation? Persistent currents remain on and monotonically increase
with increasing membrane potential.
3) Do the activation and inactivation curves overlap (left figure below), allowing
a range of voltages with constant steady-state current, or are the curves
separate (right figure below), so that all currents due to the channel are
transient, i. e. short-lived and temporary, at any voltage? Recall, both
inactivation, ℎ, (if present) and activation, 𝑚, must be significantly greater
than zero for current to flow.
4) Can you estimate the values of membrane potential over which the variables
increase from zero to one (for activation) or decrease from one to zero (for
inactivation, if inactivation is present).
5) What is an approximate (at least order of magnitude) of the time constant for
changes in activation (switching the current on) and inactivation (switching
the current off), if present? Which is faster—activation or inactivation—and
why would you expect this to be the case for any useful channel? Of course, if
you decide the current is a persistent current, with no inactivation, this
second question is irrelevant.