and Korenbrot study Ih in salamander cones, showing that it is similar to the current in rods
[13, 78].
Meanwhile, Barnes et al studied the TEA sensitive component and called it Iχx, finding
that it is important in filtering smaller light responses, while ∕⅛ is more important in filtering
larger light responses. Akopian and Witovsky reported that Ih can be modulated by D2
domaminergic receptors [1], and Maclolm et al. show that it can be modulated by protons
(pH) [75]. Satoh and Yamada showed that Ih in rods could be blocked with the cardiac
If inhibitor ZD 7288 [94], which suggested that the origin of the two currents is the same.
Demontis et. al and Gargini et al performed a series of studies demonstrating that HCN1
channels are present in rabbit rods, and that the Ih current is important in maintaining the
retinas temporal response to light stimuli [30, 48, 49, 31]. They noted the similarity in its
kinetics to the cardiac If. Moosmang et al. perform immunohistochemical staining of the
mouse retina to show the distribution of HCN1-4 isoforms [82]. Later, Ivanova and Müller
along with Cangiano et. al studied the properties of Ih in retinal bipolar cells [83, 58, 26].
While this long list of contributions is not entirely comprehensive, it highlights the main
contributions to studies of Ih in the retina up to this point. Much has been learned about
this current since its discovery, but some questions remained that our studies addressed.
Namely: Is Ih the same in rods and cones, and if so, what is its function in each of these
cells? What is the conductance of single HCN channels in the retina? and Which HCN
isoforms are responsible for Ih in salamander rods and cones?