# Open state probability

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Open state probability, also written as O.S.P or Po , 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 Po 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:

#### Itotal  =  N  x  Po  x  i

Itotal =  Whole cell current

N = Number of active channels

Po = Open state probability

i = Single channel current