Let's talk about something called up and downregulations.
This is a process where the number of receptors is
dependant upon receptor binding. So at the top of our image
here, you can see that upregulation refers to
a system where you have more and more receptors being expressed
at the cell surface because there is very little activity.
So, the net result is, is that if you have low concentration
of a drug, your cell becomes more sensitive
to that drug because it has more receptors.
Downregulation or tachyphylaxis is where you have the
opposite. You have fewer and fewer receptors
because they are always being used up and broken down.
That's called downregulation and the effect on the drug is
tachyphylaxis, which is a reduced drug effect over time.