drhouse
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Increase Na(sodium) conductance means.
A. increase Na influx
B increase Na efflux
C decrease Na efflux
D decrease Na influx
E no effect on Na efflux or influx
F can not be determined
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| paganini
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a
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| silver
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A. increase Na influx
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| drhouse
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this is a basic question.
u need to think again....
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| paganini
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What it means is that Na+ channels are opening and therefore Na+ will follow the concentration gradient from out to in, is clear that after a few milliseconds the inactivation gates will prevent more Na+ influx but definately it should be at least some influx, also the na/k pump will maintain the normal concentrations. Maybe the answer you are looking for is F, do we need more Data for this? do I need Nerst equation?, I chose A assuming that other values are normal, so please give you explanation.
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| drhouse
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yeah, my ans is F.
coz i didnt specify any condition...
increase Na conductance means more Na channels are opening. it doesnt mean increase influx or efflux. influx or efflux depend on concentration gradient on either side and resting membrane potential. sometimes conductance is different than influx..
for example during initial part of the action potential conductance is minimum but influx is higher and just before peak of the aciton potential conductance is maximal but influx is minimum. so we can not determine influx solely on the base of conductance. here i didnt specified when conductance is increased. so we can not say whether Na influx will increase or decrease
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| P4a99
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maybe (F) cuz conductance means the amount of open gates despite the direction of the flux ... but in a normal cell at a normal condition, sure its going to cause an influx (depolarisation).
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| P4a99
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Good i got one correct!
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| drhouse
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yeah u right. if u mention normal condition. then it definitely gonna increase influx...
but the thing is here i didnt specify anything thats why ans is F
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| paheli
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we train ourselves to think so fast and answer so quick, that half the times, it's like a knee-jerk reflex. must admit i fell for A  . will be more careful now.
thanks for the qn, doc house.
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| new_n_lost
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Dr House........ Inc Conductance does mean Conductance across the Membrane so the Question will be Which moves across the Membrane. we all know that Na, Ca and K r the major ions that move across. Now if u r opening up a channel of any Ion wudnt it diffuse to the otherside ?? One More thing Influx Causes Conductance u r mistaken here in the concept.
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| doc179
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increased conductance to any ion ONLY means that the channels for that particular ion is open it does not say influx or eflux, so if the qn had asked in general about ion conductance then the answer would have been F, but when you say what happens to Na when its conductance is increased, obviously everyone would go for A. in USMLE you dont assume things, you just answer to the qn as it is. So generally speaking conductance does not determine the direction of ion movement. But since we know that Na goes in, we tend to go for A, but when you think about the qn F looks like the better choice, cos they have not mentioned the circumstance of neither the action potential nor the cell. I went for A at first but then I feel that they really are testing about the conductance concept here and hence it makes me go for F now.
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| new_n_lost
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Ok this is interesting Whenever is there Free Ionic Movement Isnt there a Efflux or Influx Due to Somple Diffusion. After the Channels and Gates have closed there ATPases Pumps which move the ions against their Conc. gradients.
Plz Correct me thank u 
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| doc179
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not if they are in equillibrium
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| doc179
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which is why the Na influx is very low( closer to none ) but the conductance for it is very high at the peak of the action potential.
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| new_n_lost
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doc179 wrote:
not if they are in equillibrium
sorry didnt get u
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| doc179
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if the ions are in equillibrium I mean by that ...the concetration and the eletrical forces are equal and opposite, that is the membrane potential has reached the euillibrium potential for that ion, then there wont be any influx or eflux.
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| doc179
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right !!!! looks like I answered my own doubt, see at the beginning of the action potential conductance is low and influx for Na is high and at the peak of the action potential conductance is very high and influx is zero, so that means you can not determine the flow of ion when you are given only about conductance, so the answer should be F.
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| new_n_lost
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ok i have to look it up.
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| Ig F
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itz a purely theoretical question.ththz y answer is F.
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