Lecture 19 Membrane Transport 2 Flashcards
(30 cards)
Types of Ion Channels
Voltage-gated Chemically Gated Mechanically Gated
Voltage Gated
Respond to change in membrane potential
Chemically Gated
Respond to ligands such as neurotransmitters
Mechanically Gated
Respond to mechanical stimuli, found in sensory neurons (detect vibration, pressure, stretch, touch, sounds, tastes, smell, etc.)
Patch Clamping
Proves existence of voltage gated channels
Putative Model of a Sodium Channel
260 kDa protein 4 internal repeats 6 transmembrane domains in each
In a sodium channel, which transmembrane protein is the voltage sensor?
TM 4
Putative Structure of Potassium Channel
6 transmembrane domains S1-S4 = voltage sensor S5-S6 = pore
Sodium and potassium channels are gated by membrane _____ or ______
potential or voltage
Sodium and potassium channels undergo _________ changes in response to changes in membrane potential.
Conformational
What is the ligand for acetylcholine receptor?
Acetylcholine
Where is the acetylcholine receptor located?
On the post-synaptic side
True or False: The acetylcholine receptor channel is more permeable to Na+ than K+.
False The channel is equally permeable to both Na+ and K+
Describe the Acetylcholine Receptor
Pentamer of 4 kinds of membrane spanning subunits arranged in the form of a ring that creates a pore through the membrane (2 alphas, beta, gamma, and delta)
Neurotransmission
Most important manifestation of membrane transport - the basis for communication in the nervous system
Nernst Equation
Veq = - (2.303) (RT/zF) log ([X]in/[X]out)
Describe Each Number
- Resting membrane potential (-60mV)
- Depolarization stimulus
- Na+ channels open
- Rapid Na+ entry - further depolarization
- Na+ channels close, K+ open
- K+ move out
- Membrane hyperpolarization
- K+ channels close
- Cells return to resting potential
Describe the steps of Synaptic Transmission
- AP reaches presynaptic terminal
- Depolarization opens up the VGCC
- Calcium enters cell
- Caused fusion of synaptic vesicles
- Exocytosis - release of NT in synaptic cleft
- NT bind to its receptor on post-synaptic side
- Opens up a lingand-gated channel
Gap Junctions
Special form of ion channels
“Cell to Cell” channels
Important in cell to cell communication
Structural Features of Gap Junctions
Packed in hexagonal array
Lumen ~20A
Distance between gap junctions of 2 adjacent cells is ~35A
What can pass through gap junctions?
Small hydrophilic molecules and ions
Molecules less than 1 kDa (sugars, AAs, and nucleotides)
What cannot pass through gap junctions?
Proteins, polysaccharides, and nucleic acids
Structure of Gap Junctions
Each channel is made of 12 molecules of connexin
Six connexin molecules are hexagonally arrayed to form a half channel called connexon
Two connexons join end to end in intercellular space to form functional channel
Why are gap junctions important in cardiac tissue?
Gap junctions ensure synchronous response to stimuli
