QUESTIONS 1.What type of ion channels are the MACs in our neuron? They are mecha

Question

QUESTIONS

1.What type of ion channels are the MACs in our neuron? They are
mechanically?gated, but are they only permeable for a particular ion species or are they
unselectively permeable for all kinds of anions and/or cations? If they are permeable for one
specific ion species which one listed in Table 1 is the most likely candidate?  

2.Formulate a hypothesis describing (and explaining why you come to this conclusion) the
Type of Ion Channel our MACs are, i.e. for what ion species they are permeable. (8 pts)

3.Describe a strategy for a follow?up experiment that you could do to verify your
hypothesis, i.e. confirm what ion species is able to flow through these MACs. (6 pts).

Scenario: For our project we use cultured mechanosensory neurons. These neurons are well established model cells with intracellular and extracellular ionic environments known (listed in Table 1). Previously you calculated important parameters like equilibrium potentials (E) for Na*, K', Ca2', Mg, and CI, and the membrane resting potential (VM) (Table 2; use the listed numbers!). All experiments are carried out at 30 C. Goal of you study is to determine the nature of mechanically activated ion channels (MACs) fond in these neurons. The drugs TTX (to bloclk voltage-gated Na*-channels) and TEA (to block voltage-gated K-channels) has been applied to prevent voltage-gated channels to open and influence the observed MAC-currents. lon Extracellular Concentration Intracellular Concentration Membrane Permeability P in resting neuron Na K+ 240 mM 8.5 mM 5 mM 6 mM 580 mM 37 mM 340 mM 0.02 mM 0.08 mM 55 mM 10 100 Not significant Not significant 24 Table 1 Intracellular and extracellular ion concentrations, and membrane ion permeabilities of the resting cell membrane of mechanosensory neurons (from Assignment #1, we can assume that ion concen tration do not change during the experiments. ENG+ +0.0488 V 0.0963 V +0.0721 V +0.0564 V 0.0622 V 0.0616 V +48.8 mV 96.3 mV +72.1 mV +56.4 mV 62.2 mV 61.6 mV Eca2* VM Table 2: Equilibrium potentials and membrane resting potential of mechanosensory neurons.

Explanation / Answer

The conversion of physical force into biochemical signals is needed for various biological and physiological processes, MAC ( Mechanically Activated Ion Channels) have been proposed to be the sensor of this physical force.

2. Different type of MAC are responsible for different type of functions:- The epithelial sodium channel, or amiloride sodium channel help in sodium reabsorbtion in lungs and kidneys. The acid sensing ion channel, a neronal voltage insensitive sodium channel, help in pain sensation and fear conditioning. The transient receptor potential channel help in touch smell taste and osmotic regulation. Stretch activated ion channels are related to a number of pathologies such as cardiac arrythmias, cardiac hypertropies. So, hypothetically we can say that, a mechanosensitive channel which is responsible for particular function does permit a particular ion to pass through it. As we all know sodium is essentialy needed for depolarisation, on a resting neuron 3 sodium are pumped out for every 2 potassium pumped in. This mechanism when applies to mechanosensitive stretch receptor, it does a conversion of physical stimulus into biochemical signal and here both sodium and potassium plays an invariable role, but the gated channels of potassium are selective over other cation, this selevtivity depends on amino acid sequence and narrowest part of transmembrane pore.

3. The understanding of MAC's structure and function has increased greatly nowadays, and several have been cloned. Specifically, the cloned eukaryotic mechanosensitive channels include the K+ selective 2P domain channels and the recently cloned cation selective PIEZO family. The best known MAC ion channels are the potassium channelsTREK1 and TRAAK, both of which are also found in human neuron, a new MAC ion channel family was cloned, with two members,PEIZO 1 and PEIZO 2 .

For testing my hypothesis we can select a stretch activated bone cell. It is found in variety of bone and other cells such as osteoblast cell. The basis of this test is micro pipette aspiration and cellular belb formation.

Also in prokaryots small conductance channel from a transmembrane is either MscK or MscM, different electrophysiological test with single cell mutation reveals the anion / cation selectivity depends mostly on beta- barrier.

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