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. 2006 Nov;128(5):561–567. doi: 10.1085/jgp.200609599

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Copyright © 2006, The Rockefeller University Press

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Figure 1. — Basic characterization of single HCN2 channels. (A) Two traces showing multiple openings (downward deflections) in an excised, inside-out patch in response to a voltage step to −120 mV, in the absence of cAMP. Seal resistance was ∼62 GΩ. (B) Single channel current–voltage relationship for openings in a patch with 1 mM cAMP. Linear fit is extrapolated to the origin; fitted slope conductance = 1.65 pS. (C, left) Response of a multichannel patch to a voltage step to −120 mV in presence and absence of 1 mM cAMP. Cyclic AMP increased the activation kinetics and open probability. Dotted line indicates zero current. (C, right) the Np_o-V relationship constructed from this same patch in the presence (filled circles) and absence (open circles) of 1 mM cAMP. Channels were activated by hyperpolarization, and 1 mM cAMP shifted the voltage dependence of openings to more positive potentials. These curves are only slightly more left shifted than g-V's from typical excised patch recordings of macroscopic HCN2 currents in 293 cells (midpoints of approximately −115 and −100 mV with and without cAMP), perhaps because of their long excision times.