COMPARISON OF PROPERTIES OF PORES, CHANNELS, AND CARRIERS PORES CHANNELS CARRIERS Example Water channel(AQP1) Shaker K channel Glucose transporter(GLUT1) Conduit through membrane Always open Intermittently open Never open Unitary event None(continuously open) Opening Cycle of conformational changes Particles translocated per"event" 6×104 5 Particles translocated per second up to 2 X 109 106-10 s when open200-50,000 Assuming a 100-ps channel, a driving force of 100 mV, and an opening time of 1 ms