robin082006
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Under normal physiologic conditions, which transporter will move a net positive charge into the cytosol of a resting cardiac muscle cell during phase 4 of the action potential?
A. .gif) A plasmalemma sodium3-calcium1 exchanger
B.  A lysosomal V-type proton ATPase
C. .gif) A mitochondrial F-type ATP synthetase
D. A plasmalemma sodium3-potassium2 ATPase
E. A sarcoplasmic reticulum calcium ATPase
Edited by robin082006 on 03/27/06 - 08:29 AM
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| Doc2378
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B?
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| win
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Is it D?
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| Doc2378
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nope...can't be D...it will make the cell interior negative and move it away from threshold
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| doc179
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I too feel it is D, boss, because Na+K+ATPase brings it to resting membrane potential. Here is a figure to understand it:
http://connection.lww.com/Products/morton/documen...
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| robin082006
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| sarika
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A maybe Na Ca Exchange
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| reet
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A.... Na ca exch???
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| Doc2378
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ok guys B is the only one that is going to move a net postive charge inside the cell via a H+....so it should depolarize the cell...other would be making the interior of the cell more negative...
Well?
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| robin082006
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A is correct ans
this is kaplan's but I changed the order of answer choices
I will post the explanation
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| robin082006
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The correct answer is A. Sodium has a valence of +1, whereas calcium has a valence of +2. At the resting membrane potential of approximately –90 mV in cardiac muscle cells, this transporter moves three sodium into the cell in exchange for each calcium moving out of the cell. This moves a net positive charge into the cell cytosol.
Lysosomal V-type proton ATPases move positively charged protons into the lysosome to acidify it.
Under physiologic conditions, positively charged protons move through the mitochondrial F-type ATP synthetases from the intermembrane space of the mitochondria into the matrix of the mitochondria, forcing the transporter to make ATP.
The plasmalemma sodium3-potassium2 ATPase pumps three sodium out of the cell in exchange for the two potassium being pumped into the cell; this moves a net positive charge out of the cell cytosol.
The sarcolemmal calcium ATPase pumps calcium, thus a net positive charge, out of the cytosol into the sarcoplasmic reticulum
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| Doc2378
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thanks robin...got it!...didn't notice the word 'lysosome' in front of choice B..arrrrgh!
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