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instantaneous current-voltage relation question

Xiaoshen Li xli6 at gmu.edu
Mon Dec 22 05:52:29 EST 2003


Hi, Everybody:

I have a question from Johnston & Wu's textbook(Foundations of Cellular 
Neurophysiology). It is about instantaneous current-voltage relation.

A figure shows that the neuron's steady-state current is -1 nA/um^2 at 
both Vm=-80mV and -100mV; the neuron's instantaneous current is -0.2 
nA/uM^2 at both Vm=-80mV and -100mV. Question: If the neuron is hold 
Vh=-80mV for a long period of time and jump to Vc=-100mV, what is the 
current trace look like?

The answer from the book(p46) is: the current is a flat line at -1 
nA/um^2 (there is a flip at the time of voltage change due to capacitance).

My intended answer: the current was at -1 nA/um^2 before the voltage 
change. When voltage changes, the current jump to -0.2 nA/um^2, then 
relaxes with certain time contant to -1 nA/um^2 steady-state current.

I think when author or anybody mentions instantaneous current, he should 
mention what the prepulse voltage is. Here, the author doesn't say it.

Thank you very much. I greatly appreciate your help.

Best Regards,
Xiaoshen




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