Lecture 27: Transporter & Ion Channels

Transporters

Is selective and uses either Active transport to move against a gradient→via ATP hydrolysis or disapation of a gradient. Or Passive using facilitative diffusion

Primary active transport

transport utilizing ATP for energy

Secondary Active Transport

transporting utilizing a pre-existing gradient

Ion Channels

are gated (voltage or ligand activated) and only work by facilitated diffusion, are still selective

Uniport

a transporter that moves only one species

Cotransport

a transporter that moves multiple species

Symport

a transporter that moves two species in the same direction

Antiport

a transporter that moves two species in opposite directions

Energy obtained from a gradient

ΔG = 2.303RT log (c1/c2) ± zFΔV

→z=ionic charge, F=Faraday’s constant, ΔV= membrane potential, c1 = starting concentration, c2= ending concentration

GLUT1

common in blood brain barrier and red blood cells. Uses passive transport to move glucose down its concentration gradient. Two conformations:

• T1: open on one side where glucose binds

• T2: flips to other side to deposit glucose

Rocker-Switch Mechanism

in GLUT1, describes how it transports glucose by alternating between two main states: an outward-open conformation that faces the outside of the cell and an inward-open conformation that faces the inside

Na-K ATPase

a protein in the cell membrane that uses the energy from ATP to transport three sodium ions out of the cell and two potassium ions into the cell. Maintains the electrochemical gradient essential for many physiological processes

P-type ATPase

using ATP for the phosphorylation of conserved Asp

Ca-ATPase

a pump using ATP for muscle contraction

H-K ATPase

pump using ATP to maintain stomach PH

4 domains of P-type ATPase

• Transmembrane

• Nucleotide-binding (N) → ATP

• Phosphorylation (P) → aspartate

• Actuator (A) → passes changes onto rest of structure

SERCA

a Ca-ATPase that functions as a primary active transporter. Uses ATP hydrolysis to pump Ca ions against gradient, playing a crucial role in regulating intracellular calcium levels during function

Eversion

the transporter protein changes its three-dimensional shape to move the bound substrate to the other side of the membrane

Cardiotonic Steriods

used to treat congestive heart failure, bind to the E2-P conformation of Na-K ATPase to prevent hydrolysis. This reduces the Na gradient, decreasing Ca exchange. A greater Ca contents enhances cardiac muscle contraction

→ex: Digitalis and Oubain

Secondary Transporters

use movement of one species down it’s gradient to drive the movement of a second species against it’s gradient

Na-Ca exchanger

a secondary transporter that transports 3 Na in and 1 Ca out

Lactose permease

a secondary transporter that transports a H+ in and lactose in by eversion

Na-glucose transporter

a secondary transporter that transports 2 Na in and a glucose out

Na+ Voltage Gated Channel

made of a fast activated gate, that is closed at rest and opens on depolarization, and a slow inactivation gate, that is open at rest and closes on depolarization

K+ Voltage Gated Channel

a type of voltage-gated potassium channel, which are protein pores in a cell membrane that open or close in response to changes in the cell's electrical potential (voltage). These channels allow potassium ions to flow across the membrane and are critical for regulating the excitability of cells, such as neurons and muscle cells.