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
Channelopathies离子通道病 Examples of channelopathies in excitable cells: periodic paralysis(eg, Kir2. 1, a K+ channel subunit, or Nav21, a Na+ channel subunit myasthenia(eg, nicotinic acetyl choline receptor, a ligand-gated nonspecific cation channel) myotonia(eg, Kir1. 1, a K+ channel subunit) malignant hypothermia(ryanodine receptor, a Ca2+ channel) long Qt syndrome(both Na+ and K+ channel subunit examples), etc. Examples of channelopathies in nonexcitable cells cystic fibrosis (CFTR, a Cl-channel) Bartter syndrome(Kir1. 1, a K+ channel subunit), etc
Channelopathies离子通道病 • Examples of channelopathies in excitable cells： ▫ periodic paralysis (eg, Kir2.1, a K+ channel subunit, or Nav2.1, a Na+ channel subunit) ▫ myasthenia (eg, nicotinic acetyl choline receptor, a ligand-gated nonspecific cation channel) ▫ myotonia (eg, Kir1.1, a K+ channel subunit) ▫ malignant hypothermia (ryanodine receptor, a Ca2+ channel) ▫ long QT syndrome (both Na+ and K+ channel subunit examples), etc. • Examples of channelopathies in nonexcitable cells： ▫ cystic fibrosis (CFTR, a Cl– channel) ▫ Bartter syndrome (Kir1.1, a K+ channel subunit)， etc