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Paving the way for designing drugs targeting TMEM16A
Full text linkThe calcium-activated chloride channel TMEM16A is involved in several physiological processes and is an important pharmacological target. Dinsdale and colleagues recently unveiled several residues in the outer pore region that constitute a critical site for the design of drugs that modulate TMEM16A channels
Temporal development of cyclic nucleotide-gated and Ca2+ -activated Cl- currents in isolated mouse olfactory sensory neurons
No full textA Ca(2+)-activated Cl(-) current constitutes a large part of the transduction current in olfactory sensory neurons. The binding of odorants to olfactory receptors in the cilia produces an increase in cAMP concentration; Ca(2+) enters into the cilia through CNG channels and activates a Cl(-) current. In intact mouse olfactory sensory neurons little is known about the kinetics of the Ca(2+)-activated Cl(-) current. Here, we directly activated CNG channels by flash photolysis of caged cAMP or 8-Br-cAMP and measured the current response with the whole cell voltage-clamp technique in mouse neurons. We measured multiphasic currents in the rising phase of the response at -50 mV. The current rising phase became monophasic in the absence of extracellular Ca(2+), at +50 mV, or when most of the intracellular Cl(-) was replaced by gluconate to shift the equilibrium potential for Cl(-) to -50 mV. These results show that the second phase of the current in mouse intact neurons is attributed to a Cl(-) current activated by Ca(2+), similarly to previous results on isolated frog cilia. The percentage of the total saturating current carried by Cl(-) was estimated in two ways: 1) by measuring the maximum secondary current and 2) by blocking the Cl(-) channel with niflumic acid. We estimated that in the presence of 1 mM extracellular Ca(2+) and in symmetrical Cl(-) concentrations the Cl(-) component can constitute up to 90% of the total current response. These data show how to unravel the CNG and Ca(2+)-activated Cl(-) component of the current rising phase
Whole-cell recordings and photolysis of caged compounds in olfactory sensory neurons isolated from the mouse
No full textThe blocking effect of l-cis-diltiazem on the light-sensitive current of isolated rods of the tiger salamander
No full textThe effect of the organic compound l-cis-diltiazem on the light-sensitive current of isolated rods of the tiger salamander was analysed by rapidly changing the extracellular medium using the method of Hodgkin et al. (1985). Addition to the extracellular medium of small amounts of l-cis-diltiazem rapidly inhibits the photocurrent. Complete suppression of the current was observed with 1 mM l-cis-diltiazem. Half blockage of the photocurrent occurred with about 150 microM l-cis-diltiazem. The blocking effect of l-cis-diltiazem was enhanced by light and by a reduction of extracellular Na. A concentration of l-cis-diltiazem of 140 microM, which suppresses one third of the photocurrent, was able to completely suppress the photocurrent carried by Ba. It is suggested that l-cis-diltiazem blocks the light-sensitive channel, possibly competing with cyclic guanosine-3'-5'-monophosphate (cGMP) for an internal regulatory site
The effect of cadmium on the light-sensitive current of isolated rods of the tiger salamander
No full textThe effect of cadmium on the light-sensitive current of isolated rods of the tiger salamander was analysed by rapidly changing the ionic medium using the technique of Hodgkin et al. (1985). Addition of millimolar amounts of cadmium to the extracellular medium caused a rapid, but transient, decrease of the photocurrent. The effect of cadmium on the movement of divalent cations, such as Ba2+ and Ca2+, differs according to the experimental protocol: when cadmium is introduced into the bathing medium at the same time as Ca2+ or Ba2+, it blocks the entry of these ions into the rod; and when the rod is exposed to cadmium first for a few seconds the entry of Ca2+ and Ba2+ is enhanced. The effect of cadmium is best explained as a dual effect: firstly, an external effect on the channel, and secondly, by metabolic changes, which are caused by a drop of intracellular Ca2+
Voltage-activated current properties of male and female mouse vomeronasal sensory neurons: sexually dichotomous?
No full textThe vomeronasal organ, the chemosensory organ of the vomeronasal system, is vital in determining sexual and gender-specific behavior in mice. Here, whole-cell voltage-activated currents of individual mouse vomeronasal sensory neurons of two strains (BALB/c and CBA) were measured and correlated to sex in each strain. The average resting membrane potentials, maximal outward current magnitudes, and kinetics of activation and inactivation, were found to be independent of sex. Maximal inward current magnitudes differed significantly across gender in CBA, whereas they did not significantly differ in male and female BALB/c mice: BALB/c males -347 +/- 45 pA (n = 51), and females -430 +/- 56 pA (n = 27); CBA males -308 +/- 36 pA (n = 56) and females -155 +/- 118 pA (n = 28). These results suggest that some voltage-activated properties may differ slightly according to gender and to strain
Anion Selectivity and Blockers of the Calcium-Activated Chloride Current in Mouse Olfactory Sensory Neurons
No full textAnoctamin 2/TMEM16B: A calcium-activated chloride channel in olfactory transduction
Full text linkIn vertebrate olfactory transduction, a Ca2+-dependent Cl- efflux greatly amplifies the odorant response. The binding of odorants to receptors in the cilia of olfactory sensory neurons activates a transduction cascade that involves the opening of cyclic nucleotide-gated channels and the entry of Ca2+ into the cilia. The Ca2+ activates a Cl- current that, in the presence of a maintained elevated intracellular Cl- concentration, produces an efflux of Cl- ions and amplifies the depolarization. In this review, we summarize evidence supporting the hypothesis that anoctamin 2/TMEM16B is the main, or perhaps the only, constituent of the Ca2+-activated Cl- channels involved in olfactory transduction. Indeed, studies from several laboratories have shown that anoctamin 2/TMEM16B is expressed in the ciliary layer of the olfactory epithelium, that there are remarkable functional similarities between currents in olfactory sensory neurons and in HEK 293 cells transfected with anoctamin 2/TMEM16B, and that knockout mice for anoctamin 2/TMEM16B did not show any detectable Ca2+-activated Cl- current. Finally, we discuss the involvement of Ca2+-activated Cl- channels in the transduction process of vomeronasal sensory neurons and the physiological role of these channels in olfaction. © 2011 The Authors. Experimental Physiology © 2012 The Physiological Society
Signal transduction in vertebrate olfactory Cilia
No full textThe initial steps of olfaction occur in primary sensory neurons located in the olfactory epithelium of the nasal cavity of vertebrates. These neurons are responsible for the detection of odorant molecules present in the surrounding environment and the generation of the neural signal that is transmitted to the brain. The morphology of the primary sensory neurons was described by Max Schultze in the second half of the nineteenth century (for review, see Zippel 1993), but only about 100 years later the first reviews describing some functional properties of these neurons were published (Getchell 1986; Lancet 1986). Primary sensory neurons of the olfactory epithelium, often indicated by various names: olfactory receptor cells (ORCs), olfactory sensory neurons (OSNs), or olfactory receptor neurons (ORNs), are bipolar neurons with a single dendrite that terminates with a knob, from which several tiny cilia protrude, where the transduction of the olfactory signal takes place. Odorant molecules bind to odorant receptors, and this interaction triggers an increase in the intraciliary concentration of cyclic adenosine monophosphate (cAMP) through the activation of the receptor-coupled G-protein and adenylyl cyclase (AC). Cyclic nucleotide-gated (CNG) channels located in the ciliary membrane are directly activated by cytoplasmic cAMP, causing a depolarizing influx of Na+ and Ca+ ions. The odorant-induced inward transduction current has been shown to be composed not only of a cation influx through CNG channels, but also of a Cl efflux through Cl channels activated by Ca2+ (Cl(Ca) channels). This chapter will review the molecular mechanisms underlying the functional role of vertebrate olfactory cilia
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