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Unformatted text preview: The K + channel has one open and four closed states with probabilistic transitions given by a n and b n from the HodgkinHuxley model. Long voltage pulses under K +channel blockade cause fluctuating Na + currents. Time (ms) Singleevent Responses x 2 = 1 n x i x ( ) 2 i = 1 n The variance of a random variable x is Where the overbar indicates mean and n is the sample size. Opening the square gives x 2 = x i 2 i = 1 n n 2 x x i i = 1 n n + x 2 = 1 n x i 2 i = 1 n x 2 i 2 = pi 2 p 2 i 2 For a single channel with current i and open probability p, the mean current is p*i and For N independent and identical channels, the mean is I=N*p*i and the variances sums to give I 2 = Npi 2 Np 2 i 2 = iI 1 p ( ) i = I 2 I 1 p ( ) The probability of channel opening obeys a binomial distribution, which becomes Poisson when p is small and N is large. is large....
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 Spring '09
 Grzywacz

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