The name is absent

23

properties of HCN channels in salamander rod and cone photoreceptors using the non-
Stationary fluctuation analysis (NSFA) method. By comparing single channel conductance
with whole-cell currents, we estimate the total number of channels and the channel density
in rods and cones. We also demonstrate via immunohistochemistry, single channel con-
ductance, and analysis of kinetic data of whole cell currents, that Ih in salamander rods and
cones is mediated by the HCN1 isoform.

In contrast to the heart and CNS, where HCN channels generate rhythmic potentials,
HCN channels in the retina do not cause oscillations, but instead help shape the potentials
that encode light stimuli. Evidence suggests HCN channels are necessary for the retinas
temporal response to light stimuli [49, 48, 50]. The 7⅛ current, along with another ionic
conductance dubbed Iχx, have been shown to create a bandpass filter effect in rod photore-
ceptors [5, 17, 34, 87, 103, 30, 19]. It is not clear, however, how the electrical properties of
HCN channels contribute to the dynamics of rod and cone signaling, or whether these pro-
cesses differ in the two types of photoreceptors. In this study, we use frequency chirped and
gaussian white noise (GWN) modulated current and light stimuli to directly demonstrate
how HCN channels speed up the voltage response of rods and cones. Our results show that
HCN channels contribute to photoreceptor dynamics not only in response to bright flashes,
where signal clipping is a factor, but also under physiologic light levels, and have varying
degrees of effect in rods and cones at different adaptational conditions.

<<   29   30   31   32   33   34   35   >>

More intriguing information