A cyclic nucleotide-dependent chloride conductance in olfactory receptor neurons

Cryogenic "Iodide-Tagging" Photoelectron Spectroscopy: A Sensitive Probe for Specific Binding Sites of Amino Acids

This work showcases cryogenic and temperature-dependent "iodide-tagging" photoelectron spectroscopy to probe specific binding sites of amino acids using the glycine-iodide complex (Gly·I^-) as a case study. Multiple Gly·I^- isomers were generated from ambient electrospray ionization and kinetically isolated in a cryogenic ion trap. These structures were characterized with temperature-dependent "iodide-tagging" negative ion photoelectron spectroscopy (NIPES), where iodide was used as the "messenger" to interpret electronic energetics and structural information of various Gly·I^- isomers. Accompanied by theoretical computations and Franck-Condon simulations, a total of five cluster structures have been identified along with their various binding motifs. This work demonstrates that "iodide-tagging" NIPES is a powerful general means for probing specific binding interactions in biological molecules of interest.

Natriuretic peptides and their receptors in the central nervous system

Natriuretic peptides (NPs), including atrial, brain and C-type NPs, are a family of structurally related but genetically distinct peptides. These peptides, along with their receptors (NPRs), are long known to be involved in the regulation of various physiological functions, such as diuresis, natriuresis, and blood flow. Recently, abundant evidence shows that NPs and NPRs are widely distributed in the central nervous system (CNS), suggesting possible roles of NPs in modulating physiological functions of the CNS. This review starts with a brief summary of relevant background information, such as molecular structures of NPs and NPRs and general intracellular mechanisms after activation of NPRs. We then provide a detailed description of the expression profiles of NPs and NPRs in the CNS and an in-depth discussion of how NPs are involved in neural development, neurotransmitter release, synaptic transmission and neuroprotection through activation of NPRs.

Calcium-activated chloride channels

Calcium-activated chloride channels (CaCCs) play important roles in cellular physiology, including epithelial secretion of electrolytes and water, sensory transduction, regulation of neuronal and cardiac excitability, and regulation of vascular tone. This review discusses the physiological roles of these channels, their mechanisms of regulation and activation, and the mechanisms of anion selectivity and conduction. Despite the fact that CaCCs are so broadly expressed in cells and play such important functions, understanding these channels has been limited by the absence of specific blockers and the fact that the molecular identities of CaCCs remains in question. Recent status of the pharmacology and molecular identification of CaCCs is evaluated.

Atrial natriuretic peptide induces natriuretic peptide receptor-cGMP-dependent protein kinase interaction

Circulating natriuretic peptides such as atrial natriuretic peptide (ANP) counterbalance the effects of hypertension and inhibit cardiac hypertrophy by activating cGMP-dependent protein kinase (PKG). Natriuretic peptide binding to type I receptors (NPRA and NPRB) activates their intrinsic guanylyl cyclase activity, resulting in a rapid increase in cytosolic cGMP that subsequently activates PKG. Phosphorylation of the receptor by an unknown serine/threonine kinase is required before ligand binding can activate the cyclase. While searching for downstream PKG partners using a yeast two-hybrid screen of a human heart cDNA library, we unexpectedly found an upstream association with NPRA. PKG is a serine/threonine kinase capable of phosphorylating NPRA in vitro; however, regulation of NPRA by PKG has not been previously reported. Here we show that PKG is recruited to the plasma membrane following ANP treatment, an effect that can be blocked by pharmacological inhibition of PKG activation. Furthermore, PKG participates in a ligand-dependent gain-of-function loop that significantly increases the intrinsic cyclase activity of the receptor. PKG translocation is ANP-dependent but not nitric oxide-dependent. Our results suggest that anchoring of PKG to NPRA is a key event after ligand binding that determines distal effects. As such, the NPRA-PKG association may represent a novel mechanism for compartmentation of cGMP-mediated signaling and regulation of receptor sensitivity.

Natriuretic peptide signalling: molecular and cellular pathways to growth regulation

The natriuretic peptides (NPs) constitute a family of polypeptide hormones that regulate mammalian blood volume and blood pressure. The ability of the NPs to modulate cardiac hypertrophy and cell proliferation as well is now beginning to be recognized. The NPs interact with three membrane-bound receptors, all of which contain a well-characterized extracellular ligand-binding domain. The R1 subclass of NP receptors (NPR-A and NPR-B) contains a C-terminal guanylyl cyclase domain and is responsible for most of the NPs downstream actions through their ability to generate cGMP. The R2 subclass lacks an obvious catalytic domain and functions primarily as a clearance receptor. This review focuses on the signal transduction pathways initiated by ligand binding and other factors that help to determine signalling specificities, including allosteric factors modulating cGMP generation, receptor desensitization, the activation and function of cGMP-dependent protein kinase (PKG), and identification of potential nuclear or cytoplasmic targets such as the mitogen-activated protein kinase signalling (MAPK) cascade. The inhibition of cardiac growth and hypertrophy may be an important but underappreciated action of the NP signalling system.

Cellular and molecular constituents of olfactory sensation in vertebrates

Since the discovery of odorant-activated adenylate cyclase in the olfactory receptor cilia, research into the olfactory perception of vertebrates has rapidly expanded. Recent studies have shown how the odor discrimination starts at the receptor level: each of 700-1000 types of the olfactory neurons in the neural olfactory epithelium contains a single type of odor receptor protein. Although the receptors have relatively low specific affinities for odorants, excitation of different types of receptors forms an excitation pattern specific to each odorant in the glomerular layer of the olfactory bulb. It was demonstrated that adenosine 3',5'-cyclic monophosphate (cAMP) is very likely the sole second messenger for olfactory transduction. It was also demonstrated that the affinity of the cyclic nucleotide-gated channel for cAMP regulated by Ca(2+)/calmodulin is solely responsible for the adaptation of the cell. However, many other regulatory components were found in the transduction cascade. Regulated by Ca(2+) and/or the protein-phosphorylation, many of them may serve for the adaptation of the cell, probably on a longer time scale. It may be important to consider the resensitization as a part of this adaptation, as well as to collect kinetic data of each reaction to gain further insight into the olfactory mechanism.

Neuronal Ca2+ -activated Cl- channels--homing in on an elusive channel species

Ca2+ -activated Cl- channels control electrical excitability in various peripheral and central populations of neurons. Ca2+ influx through voltage-gated or ligand-operated channels, as well as Ca2+ release from intracellular stores, have been shown to induce substantial Cl- conductances that determine the response to synaptic input, spike rate, and the receptor current of various kinds of neurons. In some neurons, Ca2+ -activated Cl- channels are localized in the dendritic membrane, and their contribution to signal processing depends on the local Cl- equilibrium potential which may differ considerably from those at the membranes of somata and axons. In olfactory sensory neurons, the channels are expressed in ciliary processes of dendritic endings where they serve to amplify the odor-induced receptor current. Recent biophysical studies of signal transduction in olfactory sensory neurons have yielded some insight into the functional properties of Ca2+ -activated Cl- channels expressed in the chemosensory membrane of these cells. Ion selectivity, channel conductance, and Ca2+ sensitivity have been investigated, and the role of the channels in the generation of receptor currents is well understood. However, further investigation of neuronal Ca2+ -activated Cl- channels will require information about the molecular structure of the channel protein, the regulation of channel activity by cellular signaling pathways, as well as the distribution of channels in different compartments of the neuron. To understand the physiological role of these channels it is also important to know the Cl- equilibrium potential in cells or in distinct cell compartments that express Ca2+ -activated Cl- channels. The state of knowledge about most of these aspects is considerably more advanced in non-neuronal cells, in particular in epithelia and smooth muscle. This review, therefore, collects results both from neuronal and from non-neuronal cells with the intent of facilitating research into Ca2+ -activated Cl- channels and their physiological functions in neurons.

Lysophosphatidic acid stimulates neurotransmitter-like conductance changes that precede GABA and L-glutamate in early, presumptive cortical neuroblasts

During neurogenesis in the embryonic cerebral cortex, the classical neurotransmitters GABA and L-glutamate stimulate ionic conductance changes in ventricular zone (VZ) neuroblasts. Lysophosphatidic acid (LPA) is a bioactive phospholipid producing myriad effects on cells including alterations in membrane conductances (for review, see Moolenaar et al., 1995). Developmental expression patterns of its first cloned receptor gene, lpA1/vzg-1 (Hecht et al., 1996; Fukushima et al., 1998) in the VZ suggested that functional LPA receptors were synthesized at these early times, and thus, LPA could be an earlier stimulus to VZ cells than the neurotransmitters GABA and L-glutamate. To address this possibility, primary cultures of electrically coupled, presumptive cortical neuroblast clusters were identified by age, morphology, electrophysiological profile, BrdU incorporation, and nestin immunostaining. Single cells from cortical neuroblast cell lines were also examined. Whole-cell variation of the patch-clamp technique was used to record from nestin-immunoreactive cells after stimulation by local administration of ligands. After initial plating at embryonic day 11 (E11), cells responded only to LPA but not to GABA or L-glutamate. Continued growth in culture for up to 12 hr produced more LPA-responsive cells, but also a growing population of GABA- or L-glutamate-responsive cells. Cultures from E12 embryos showed LPA as well as GABA and L-glutamate responses, with LPA-responsive cells still representing a majority. Overall, >50% of cells responded to LPA with depolarization mediated by either chloride or nonselective cation conductances. These data implicate LPA as the earliest reported extracellular stimulus of ionic conductance changes for cortical neuroblasts and provide evidence for LPA as a novel, physiological component in CNS development.