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. 2002 Jul;120(1):99–116. doi: 10.1085/jgp.20028586

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Copyright © 2002, The Rockefeller University Press

This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).

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Figure 5. — Nonstationary noise analysis of the interacting MTSET-IKCa mutants. Relationship between the current variance σ² and the mean current <I> during MTSET application illustrated for the V275C, A283C, V284C, and V285C mutants. <I> and σ² were measured on successive time periods of 1 s for A283C, V284C, and V285C and 0.5 s for V275C. The V275C mutant displayed a constant σ²/<I> (left panel right scale) ratio despite an important decrease in <I> (left panel left scale), indicating an important inhibition of the channel unitary current. This proposal is also supported by the fact that the ratio σ²/<I>² (right panel) increases in this case with a time constant equal to τi, the inhibition time constant measured for <I>. A similar noise pattern was also observed with the V284C mutant, although in this case the variations in σ²/<I> and σ²/<I>² can be accounted for a partial inhibition of the channel unitary current plus a decrease in channel open probability. A different noise behavior is, however, observed with the A283C and V285C channels. The decrease in σ²/<I>² observed with A283 correlates the increase in mean current with the σ²/<I> ratio remaining constant for time >7.5 s. This noise pattern would be compatible with a system where P_B > P_O with P_O and P_B << 1, thus supporting a model whereby the action of MTSET consists either to increase the channel open probability or recruit silent A283C mutants. The results obtained with V285C follow a similar pattern, although in this case the fact that the measured variation in σ²/<I>² is more important than the mean current increase favors a system where P_B > P_O with P_O << 1.