RP triggers permanent loss of bipolar cell glutamate receptor expression, though spontaneous iGluR-mediated signaling by amacrine and ganglion cells implies that such truncated bipolar cells still release glutamate in response to some nonglutamatergic depolarization. Focal cone-sparing can preserve iGluR display by nearby bipolar cells, which may facilitate late RP photoreceptor transplantation attempts. An instance of human RP provides evidence that rod bipolar cell dendrite switching likely triggers new gene expression patterns and may impair cone pathway function.

Background We used in vivo corneal confocal microscopy to investigate structural differences in the sub-basal corneal nerve plexus in chronic migraine patients and a normal population. We used a validated questionnaire and tests of lacrimal function to determine the prevalence of dry eye in the same group of chronic migraine patients. Activation of the trigeminal system is involved in migraine. Corneal nociceptive sensation is mediated by trigeminal axons that synapse in the gasserian ganglion and the brainstem, and serve nociceptive, protective, and trophic functions. Noninvasive imaging of the corneal sub-basal nerve plexus is possible with in vivo corneal confocal microscopy. Methods For this case–control study, we recruited chronic migraine patients and compared them with a sex- and age-similar group of control subjects. Patients with peripheral neuropathy, a disease known to be associated with a peripheral neuropathy, or prior corneal or intraocular surgery were excluded. Participants underwent in vivo corneal confocal microscopy using a Heidelberg Retinal Tomography III confocal microscope with a Rostock Cornea Module. Nerve fiber length, nerve branch density, nerve fiber density, and tortuosity coefficient were measured using established methodologies. Migraine participants underwent testing of basal tear production with proparacaine, corneal sensitivity assessment with a cotton-tip applicator, measurement of tear break-up time, and completion of a validated dry eye questionnaire. Results A total of 19 chronic migraine patients and 30 control participants completed the study. There were no significant differences in age or sex. Nerve fiber density was significantly lower in migraine patients compared with controls (48.4 ± 23.5 vs 71.0 ± 15.0 fibers/mm2, P < .001). Nerve fiber length was decreased in the chronic migraine group compared with the control group, but this difference was not statistically significant (21.5 ± 11.8 vs 26.8 ± 5.9 mm/mm2, P < .084). Nerve branch density was similar in the two groups (114.0 ± 92.4 vs 118.1 ± 55.9 branches/mm2, P < .864). Tortuosity coefficient and log tortuosity coefficient also were similar in the chronic migraine and control groups. All migraine subjects had symptoms consistent with a diagnosis of dry eye syndrome. Conclusions We found that in the sample used in this study, the presence of structural changes in nociceptive corneal axons lends further support to the hypothesis that the trigeminal system plays a critical role in the pathogenesis of migraine. In vivo corneal confocal microscopy holds promise as a biomarker for future migraine research as well as for studies examining alterations of corneal innervation. Dry eye symptoms appear to be extremely prevalent in this population. The interrelationships between migraine, corneal nerve architecture, and dry eye will be the subject of future investigations.

Hyperpolarization-activated, cyclic nucleotide-modulated (HCN) channels mediate rhythmic electrical activity of neural and cardiac pacemaker cells. Drugs that block these channels slow the beating rate of the heart and are used to treat angina. Here, we characterized the effect of the HCN channel blocker, ZD7288 [4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride] on HCN2 channels that were heterologously expressed in Xenopus oocytes. A site-directed mutagenesis approach was used to identify specific residues of the mouse HCN2 channel pore that interact with ZD7288. Two residues (Ala425 and Ile432) located in the S6 transmembrane domain were found to be the primary determinants for block of HCN2 channels by ZD7288. I432A mutant HCN2 channels were ϳ100-fold less sensitive to block by ZD7288. Substitution of Ile432 with more hydrophobic residues (Phe, Leu, or Val) caused only modest shifts in the IC 50 for the drug. HCN1 channels have a Val (Val390) in the equivalent position of Ile432 and are less sensitive to block by ZD7288. Accordingly, mutation of this Val390 to Ile in HCN1 increased the sensitivity of these channels to drug block. Mutation of Ala425 and Ile432 also attenuated the block of HCN2 by the more potent blocker cilobradine. An HCN2 homology model based on the bacterial KcsA K ϩ channel predicts that the phenyl ring of ZD7288 occupies a hydrophobic cavity formed by Ala425 and Ile432 and that the charged ring aligns with the axis of the inner pore closely corresponding to the localization of K ϩ ions observed in the KcsA crystal structure.Pacemaker channels are activated by membrane hyperpolarization and conduct an inward cation current that contributes to spontaneous activity of specialized pacemaker cells in the heart (Baruscotti et al., 2005) and synaptic integration and network rhythmicity of central neurons (Biel et al

Cd2+ slows the rate of activation, accelerates the rate of deactivation and shifts the half-points of voltage-dependent activation (V 0.5,act ) and inactivation (V 0.5,inact ) of human ether-à-go-go-related gene (hERG) K + channels. To identify specific Cd 2+ -binding sites on the hERG channel, we mutated potential Cd 2+ -coordination residues located in the transmembrane domains or extracellular loops linking these domains, including five Cys, three His, nine Asp and eight Glu residues. Each residue was individually substituted with Ala and the resulting mutant channels heterologously expressed in Xenopus oocytes and their biophysical properties determined with standard two-microelectrode voltage-clamp technique. Cd 2+ at 0.5 mM caused a +36 mV shift of V 0.5,act and a +18 mV shift of V 0.5,inact in wild-type channels. Most mutant channels had a similar sensitivity to 0.5 mM Cd Human ether-à-go-go-related gene (hERG) channel is a member of the ether-à-go-go (EAG) family of voltage-gated K + channels (Warmke & Ganetzky, 1994) and is expressed in many cell types, including cardiac myocytes, neurones and tumour cells. In cardiomyocytes, hERG channel subunits co-assemble to form homotetrameric channels that conduct the rapid delayed rectifier K + current I Kr (Sanguinetti et al. 1995; Trudeau et al. 1995). I Kr is an important component of the outward currents that mediate repolarization of the cardiac action potential. Inherited loss-of-function mutations in HERG or block of hERG channels by specific drugs prolongs the duration of action potentials and causes long QT syndrome, a disorder of ventricular repolarization that increases the risk of life-threatening arrhythmias (Keating & Sanguinetti, 2001).Divalent cations can modify ion channel gating by screening non-specific negative surface charges located on membrane lipids and proteins (McLaughlin, 1989) or by binding to specific residues of channel proteins (Gilly & Armstrong, 1982). Recent studies have attempted to localize the binding sites using site-directed mutagenesis. Several acidic residues in the S5-P linker of Kv1-Kv4 channels were proposed to account for the majority of negative surface charges that were screened by divalent cations (Elinder et al. 1996(Elinder et al. , 1998. In Drosophila EAG (dEAG) channels, Mg 2+ , Mn 2+ and Ni 2+ slow gating by binding to an extracellular site formed by two acidic residues: D278 in S2 and D327 in S3 (Silverman et al. 2000). Charge pair interactions between these Asp residues and specific basic residues in S4 have been proposed to facilitate activation of dEAG channels and protein folding and activation of Shaker channels (Papazian et al. 1995;Seoh et al. 1996; Tiwari-Woodruff et al. 1997Silverman et al. 2000Silverman et al. , 2003Silverman et al. , 2004. Specific charge pairings may be disrupted and replaced by others as the S4 helix slides past the relatively immobile S2 and S3 domains. In this scheme, divalent cations bind to the Asp residues in S2 or S3 and prevent interaction with S4, causing a slowing of EAG...