Logothetis_guide_answers - Logothetis et al(1987 The...

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Logothetis et al. (1987) The Beta-gamma subunits of GTP-binding proteins activate the muscarinic K+ channel in heart. Nature 325:321-326. These questions are intended to help you read the paper in an inquisitive fashion and to help you focus on some of the issues you should understand. 1) In this paper the authors set out to test the effect of what subunits on the muscarinic K+ channel activity? Why is the word "unexpectedly" used in the abstract? The authors set out to test the effect of various a subunits of G-proteins on muscarinic K+ channel activity. They were surprised to find that the a subunits appeared to have no detectable effect on channel activity whereas the b/g subunits mediated activation of the channel. 2) Acetylcholine binds to its receptor and causes opening of separate K+ channels in heart muscle by a G-protein-dependent pathway. How does this differ from the way in which acetylcholine initiates the depolarization of plasma membrane of skeletal muscles at the neuromuscular junction? For the neuromuscular junction, the receptor for acetylcholine is also a cation channel. Binding of acetylcholine causes a conformational change that opens the cation channel and leads to depolarization of the plasma membrane. 3) For the patch-clamp assay, the solution out-side the pipette is topologically equivalent to which: the cytoplasmic or the extracellular side of the plasma membrane? The cytoplasmic side. 4) (Not a question, just some help in interpreting the data) Much of the data is presented as plots of Npo vs time. For our purposes, the important number is the overall average of Npo under a given set of conditions, since this reflects the number of channels that are open. The average of Npo is presented as a percentage over the plot within each panel of the figure. For example, in Figure 1a, the average NPo in each experiment was 5.1,
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Logothetis_guide_answers - Logothetis et al(1987 The...

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