Ion Channels Research Paper

MED 208 – ASSIGNMENT 1

Avantika Narasimhan

2013M007

1. Define ion channels.

Ion channels are proteins present on the cell membrane. They are pore forming and they facilitate the movement of selective or non-selective ions across the cell membrane.

2. Classify ion channels.

TYPE DESCRIPTION

Voltage gated ion channels They can be opened or closed according to the changes in the membrane potential. Ex: Activation gate of Na+ channel is opened during the upstroke of action potential in depolarization.

Ligand gated ion channels They can be opened or closed by a ligand, which could be a neurotransmitter, a hormone or a second messenger. Ex: Nicotinic Acetylcholine receptor, GABA receptor.

Mechanical ion channels They can be opened or closed

Generating and maintaining RMP

The diffusion potentials of different ions establish the resting membrane potential. The concentration difference between the permanent ions like Na+ and K+ ions maintains the RMP through the Na+-K+ Pump.

b. Generation and propagation of action potential

Various ions on wither side of the cell membrane alter the membrane potential over time. Once this reaches the threshold potential, there is depolarization. This involves the opening of the Na+ channel activated gates. The changes in the electrical fields cause the opening of the ion channels, through which the ions travel along their electrochemical gradient.

6. Explain how neurotransmitters modify the activity of ion channels.

Ion channels in the post-synaptic neuron open when neurotransmitters are bound to them. Neurotransmitters can either cause an excitatory potential (depolarization) or an inhibitory potential (hyperpolarization). For the excitatory stimulus, there is a more positive resting membrane potential, with opening of Na+ channels and inhibition of Cl- or K+ channels. For the inhibitory stimulus, caused by the release of an inhibitory substance like GABA, there is opening of Cl- channels (increased –ve charge inside the cell) and more efflux of K+ to increase the outflow of positive

Describe the agonists and antagonists that act on the ion channels and their significance.

Agonists of ion channels are substances that bind into the pores of these channels and cause the channels to open and facilitate the flow of ions through them. For example, Acetylcholine (nicotinic) binds to the excitatory ionotropic Na/K receptor that is broadly distributed, including striated muscle. Similarly, Serotonin binds to the excitatory ionotropic Na/K receptor especially in the raphe nuclei, which affects the cognitive function and attentiveness. Glutamate also binds to ionotropic excitatory Na/Ca/K or NMDA/AMPA while Glycine and GABA bind to inhibitory Cl- receptor.

Antagonists of ion channels are substances that bind into the pores of these channels and block their activity. Since the flow of ions through the channels is blocked, the changes in the electrochemical gradient surrounding the membrane cause changes in transmission of signals. This can alter the transmission of nerve impulses as well as bring about other effects in the body like muscle contractions, heart rate, etc. Examples of channel blockers include Calcium channel blockers, Potassium channel blockers, Chloride channel blockers and Sodium channel