The TRPM1 channel in ON-bipolar cells is gated by both the α and the βî 3 subunits of the G-protein G o

Transmission from photoreceptors to ON bipolar cells in mammalian retina is mediated by a sign-inverting cascade. Upon binding glutamate, the metabotropic glutamate receptor mGluR6 activates the heterotrimeric G-protein Gα o β3γ 313, and this leads to closure of the TRPM1 channel (melastatin). TRPM1 is thought to be constitutively open, but the mechanism that leads to its closure is unclear. We investigated this question in mouse rod bipolar cells by dialyzing reagents that modify the activity of either Gα o or Gβγ 3 and then observing their effects on the basal holding current. After opening the TRPM1 channels with light, a constitutively active mutant of Gα o closed the channel, but wild-type Gα o did not. After closing the channels by dark adaptation, phosducin or inactive Gα o (both sequester Gβγ 3) opened the channel while the active mutant of Gα o did not. Co-immunoprecipitation showed that TRPM1 interacts with Gβ3 and with the active and inactive forms of Gα o. Furthermore, bioluminescent energy transfer assays indicated that while Gα o interacts with both the N-and the C-termini of TRPM1, Gβγ 3 interacts only with the N-terminus. Our physiological and biochemical results suggest that both Gα o and Gβγ 3 bind TRPM1 channels and cooperate to close them.Fil: Xu, Ying. Jinan University; China. Nantong University; ChinaFil: Orlandi, Cesare. The Scripps Research Institute; Estados UnidosFil: Cao, Yan. The Scripps Research Institute; Estados UnidosFil: Yang, Shengyan. Jinan University; ChinaFil: Choi, Chan-Il. Research Triangle Park; Estados UnidosFil: Pagadala, Vijayakanth. Research Triangle Park; Estados UnidosFil: Birnbaumer, Lutz. Research Triangle Park; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas; ArgentinaFil: Martemyanov, Kirill A.. The Scripps Research Institute; Estados UnidosFil: Vardi, Noga. State University of Pennsylvania; Estados Unido

Functional consequences of electrical coupling

The AII amacrine cell of mammalian retina collects signals from several hundred rods and is hypothesized to transmit quantal "single-photon" signals at scotopic (starlight) intensities. One problem for this theory is that the quantal signal from one rod when summed with noise from neighboring rods would be lost if some mechanism did not exist for removing the noise. Several features of the AII might together accomplish such a noise removal operation: The AII is interconnected into a syncytial network by gap junctions, suggesting a noise-averaging function, and a quantal signal from one rod appears in five AII cells due to anatomical divergence. Furthermore, the AII contains voltage-gated Na+ and K+ channels and fires slow action potentials suggesting that it could selectively amplify quantal photon signals embedded in uncorrelated noise. To test this hypothesis, we simulated a square array of AII somas (Rm = 25,000 Ohm-cm2) interconnected by gap junctions using a compartmental model. Simulated noisy inputs to the AII produced noise (3.5 mV) uncorrelated between adjacent cells, and a gap junction conductance of 200 pS reduced the noise by a factor of 2.5, consistent with theory. Voltage-gated Na+ and K+ channels (Na+: 4 nS, K+: 0.4 nS) produced slow action potentials similar to those found in the presence of noise. For a narrow range of Na+ and coupling conductance, quantal photon events (~5-10 mV) were amplified nonlinearly by subthreshold regenerative events in the presence of noise. A lower coupling conductance produced spurious action potentials, and a greater conductance reduced amplification. Since the presence of noise in the weakly coupled circuit readily initiates action potentials that tend to spread throughout the AII network, we spe..

Molecular analysis of neural crest migration

The neural crest (NC) cells have been called the 'explorers of the embryos' because they migrate all over the embryo where they differentiate into a variety of diverse kinds of cells. In this work, we analyse the role of different molecules controlling the migration of NC cells. First, we describe the strong similarity between the process of NC migration and metastasis in tumour cells. The epithelial-mesenchymal transition process that both kinds of cells undergo is controlled by the same molecular machinery, including cadherins, connexins, Snail and Twist genes and matrix metalloproteases. Second, we analysed the molecular signals that control the patterned migration of the cephalic and trunk NC cells. Most of the factors described so far, such as Eph/ephrins, semaphorins/neuropilins and Slit/Robo, are negative signals that prohibit the migration of NC cells into target areas of the embryo. Finally, we analyse how the direction of migration is controlled by regulation of cell polarity and how the planar cell polarity or non-canonical Wnt signalling is involved in this process

Regional differences in GABA and GAD

Mammalian horizontal cells are believed to be GABAergic because, in most species, they contain both GABA and glutamic acid decarboxylase (GAD), and their terminals are presynaptic to GABA receptors. In adult rabbit, however, GABA and GAD immunoreactivity have not been consistently demonstrated in horizontal cells, casting doubts on the assumption that they too are GABAergic. Here we demonstrate that all rabbit horizontal cell terminals---dendritic terminals of type A, and both dendritic and axonal terminals of type B---immunostain for one isoform of GAD, GAD 67 . In addition, we show that type A horizontal cell somas and primary dendrites in the visual streak (identified by their immunoreactivity to calbindin) are immunoreactive for the other GAD isoform, GAD 65