Roxanita
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Q-1 A series of experiments is performed to determine the mechanism by which a pharmacologic agent traverses cell membranes and accumulates within target cells. The rate of transport depends on the concentration of the drug only. When the extracellular concentration of the agent exceeds 10 mM, no further increase in the rate of uptake is observed. Structurally similar compounds pass through the cell membrane, but at a lower rate. Ouabain, an inhibitor of Na+/ K+ ATPase, fails to inhibit transport. Which of the following is the most likely mechanism by which this agent enters cells?
A) Antiport
B) Facilitated diffusion
C) Ion-gated coupling
D) Simple diffusion
E) Symport
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| kmp
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D) simlpe diffusion
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| MLF
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Since we know that Na/K fails to inhibit transport, that leaves us with Simple and Facilitated diffusion. Now, the question says that after reaching an extracellular concentration of 10nM, no more increase can occur, which means this must be carrier mediated as that would be the concentration at which all the carriers are saturated and can't increase the concentration anymore. The answer then would be B, Facilitated diffusion.
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| Roxanita
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Nice explanation MLF. I would also go with that answer.
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| Study.Turtle
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Nice explanation, MLF; nice pic, Roxanita. Thanks.
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| Cedrick
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Sweet
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| dr_sarim
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i agree B
but what is symport and anti port?
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| Diego Casali
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B.
No doubt.
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| vallia
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symport = cotransport, molecules move in the same direction, example cotransport of Na and glucose in the renal tubules and gut. this is secondary active transport and depends on ATP used on Na/K ATP-ase pump
antiport= countertransport, molecules move in opposite direction, like in Na/Ca antiporter in heart muscle. this is also secondary active transport, which means that need Na/K ATP-ase pump
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