The big question is: What type of ion channels are the MACs in our neuron? They

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The big question is: 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?  The results of our experiments shown in Fig. 1 allow us to come up with a solid hypothesis what kind of ion specific MACs we have to deal with.  Analyzing the current behavior at the different membrane potentials you will find the clues to solve this problem! Based on your findings and observations you will have to: I) 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)

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

ans- the MAC or mechanically activated channels are found in all the eukaryotes, bacteria and archea. this are normally associated with the smell, taste and touch like sensations. in bacteria and archea they are non spcific but in eukaryotes these are specific for the cations like Ca2+, K+ and Na+ . these are more specific for the Ek+ which is listed in the table 1 of question.

hypothesis- the cells should be treated in an environment of anions only and then the permeability should be checked. if these show permeability for the anions then the hypothesis will be wrong but if they show no permeability for the anions then the hypothesis should be considered true.

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