Another way to test for the channel versus mobile carrier mechanism is to use a higher cholesterol content. Increasing the amount of cholesterol in the POPC/cholesterol membrane decreases the fluidity of the membrane, which should decrease the mobility of carriers. A transmembrane channel, however, should not be affected, as it spans the whole membrane. Usually, a dramatic change from 30% to 40-50% cholesterol is observed, thought to be caused by the "super-toughening" effect of the vesicle membrane when increasing the cholesterol content above 30%.