Abstract
Gating of cyclic nucleotide gated (CNG) channels is thought not to be voltage dependent. However, in the presence of symmetrical Rb+ and Cs+ CNGA1 channels exhibit a clear voltage and time dependent gating of macroscopic current. In symmetrical Rb+ and Cs+ the single channel conductance (γsc) and the open probability (Pop) of w.t. CNGA1 channels are highly voltage dependent: Pop increases 2-4 times at positive voltages and γsc is larger at negative voltages. In the presence of Na+ and K+, rapid channel closures and the observed residual voltage dependence of γsc and the Pop are eliminated when the S4 domain is blocked by anchoring to it large sulphydryl reagents. γsc becomes very similar at positive and negative voltages when Glu363 in the pore is replaced by Alanine. These result uncover two major properties of CNGA1 channels, not yet properly evidentiated. Firstly, CNGA1 channels, in contrast to what usually believed, sense voltage and the S4 domain plays an important role in voltage sensing. Secondly, permeation and gating are coupled through a voltage sensor and that Glu363 is the major constituent of it.
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