Open state probability

 Open state probability, also written as O.S.P or P_{o ,} is a measure of the proportion of the total recording time that an ion channel spends in its open state. 

O.S.P = Open state time / Total recording time

(which can be written as a percentage when the answer is multiplied by 100)

• This is a useful way for channels to change their activity as their conductance cannot be changed but the amount of time they spend closed or opened can.
• This can usually be found out by using the patch clamp technique and measuring the single channel recording over a certain period of time. This will be able to tell us the open state probability of that channel as well as its conductance and selectivity.

The P_o value is useful when counting the number of ion channels (N) in a cell because we are able to substitute its value (along with the rest of the values) into the following equation:

I_total  =  N  x  P_o  x  i

I_total =  Whole cell current

N = Number of active channels

P_o = Open state probability

i = Single channel current