Mechanosensitive Piezo Channels in the Gastrointestinal Tract.

Sensation of mechanical forces is critical for normal function of the gastrointestinal (GI) tract and abnormalities in mechanosensation are linked to GI pathologies. In the GI tract there are several mechanosensitive cell types-epithelial enterochromaffin cells, intrinsic and extrinsic enteric neurons, smooth muscle cells and interstitial cells of Cajal. These cells use mechanosensitive ion channels that respond to mechanical forces by altering transmembrane ionic currents in a process called mechanoelectrical coupling. Several mechanosensitive ionic conductances have been identified in the mechanosensory GI cells, ranging from mechanosensitive voltage-gated sodium and calcium channels to the mechanogated ion channels, such as the two-pore domain potassium channels K2P (TREK-1) and nonselective cation channels from the transient receptor potential family. The recently discovered Piezo channels are increasingly recognized as significant contributors to cellular mechanosensitivity. Piezo1 and Piezo2 are nonselective cationic ion channels that are directly activated by mechanical forces and have well-defined biophysical and pharmacologic properties. The role of Piezo channels in the GI epithelium is currently under investigation and their role in the smooth muscle syncytium and enteric neurons is still not known. In this review, we outline the current state of knowledge on mechanosensitive ion channels in the GI tract, with a focus on the known and potential functions of the Piezo channels.

The additional ACh binding site at the α4(+)/α4(-) interface of the (α4ß2)2α4 nicotinic ACh receptor contributes to desensitization.

BACKGROUND AND PURPOSE: Nicotinic ACh (α4ß2)2α4 receptors are highly prone to desensitization by prolonged exposure to low concentrations of agonist. Here, we report on the sensitivity of the three agonist sites of the (α4ß2)2α4 to desensitization induced by prolonged exposure to ACh. We present electrophysiological data that show that the agonist sites of the (α4ß2)2α4 receptor have different sensitivity to desensitization and that full receptor occupation decreases sensitivity to desensitization. EXPERIMENTAL APPROACH: Two-electrode voltage-clamp electrophysiology was used to study the desensitization of concatenated (α4ß2)2α4 receptors expressed heterologously in Xenopus oocytes. Desensitization was assessed by measuring the degree of functional inhibition caused by prolonged exposure to ACh, as measured under equilibrium conditions. We used the single-point mutation α4W182A to measure the contribution of individual agonist sites to desensitization. KEY RESULTS: (α4ß2)2α4 receptors are less sensitive to activation and desensitization by ACh than (α4ß2)2ß2 receptors. Incorporation of α4W182A into any of the agonist sites of concatenated (α4ß2)2α4 receptors decreased sensitivity to activation and desensitization but the effects were more pronounced when the mutation was introduced into the α4(+)/α4(-) interface. CONCLUSIONS AND IMPLICATIONS: The findings suggest that the agonist sites in (α4ß2)2α4 receptors are not functionally equivalent. The agonist site at the α4(+)/α4(-) interface defines the sensitivity of (α4ß2)2α4 receptors to agonist-induced activation and desensitization. Functional differences between (α4ß2)2α4 and (α4ß2)2ß2 receptors might shape the physiological and behavioural responses to nicotinic ligands when the receptors are exposed to nicotinic ligands for prolonged periods of times.

Coccidias aviares de gallineros industriales de Chile / Avian coccidia in poultry farms from Chile

Con el objeto de identificar las especies de coccidias existentes en los gallineros industriales de Chile, se analizaron 51 muestras fecales (de 50 deposiciones de pollos cada muestra) provenientes de 8 planteles avícolas ubicados en la Región Metropolitana, II, V y VI Región. A una parte de las muestras (10 por ciento) se les sometió a exámenes coprológicos de flotación para identificar preliminarmente los ooquistes de coccidias presentes. Paralelamente, a la parte restante de la muestra, se la suspendió en una solución de bicromato de potasio al 2,5 por ciento, hasta que completara la esporulación de sus ooquistes. Los ooquistes así esporulados se administraron a 6 pollitos broiler de 21 días de edad, libres de infección por coccidias, en los cuales se identificaron las especies de Eimeria, según su prepatencia, el tamaño de esquizontes, y el tipo y localización de las lesiones producidas en los intestinos. Las lesiones se estudiaron macro y microscópicamente. De las 51 muestras estudiadas se encontraron 7 especies de coccidias cuya frecuencia y porcentaje de presentación fue respectivamente la siguiente: E. maxima 24 (48 por ciento); E. praecox 31 (62 por ciento); E. mitis 34 (68 por ciento); E. tenella 7 (14 por ciento); E. necatrix 7 (14 por ciento); E. mivati 4 (8 por ciento); y E. acervulina 24 (48 por ciento). No se encontraron Eimeria brunetti y Eimeria hagani. Las infecciones mixtas fueron más frecuentes que las por una sola especie de coccidia, predominando las infecciones mixtas por 3-4 especies

Enfermedad de Lyme en Chile: estudio de prevalencia en grupos seleccionados / Lyme's disease in Chile: prevalence study in selected groups

The prevalence of Lyme disease in Chile is unknown. To study the existence and epidemiology of Lyme Disease in Chile. One hundred eighteen patients with signs or symptoms suggestive of Lyme disease were studied. Antibodies against Borrelia burgdorferi were measured using ELISA and indirect immunofluorescence screening tests. Positive cases were confirmed with ELISA using a purified antigen and Western Blot analysis. Human biological samples and ticks were cultured in BSK-H medium. Five patients, 3 with dermatological manifestations and two with facial palsy and other neurological symptoms, had antibodies against Borrelia, measured by ELISA and indirect immunofluorescence. However, the presence of IgM antibodies by ELISA using purified antigen, was confirmed in only one case. All sera and cerebrospinal fluids were negative on Western Blot analysis. No plasma, skin, CFS or thick culture yielded Borrelia. We could not confirm the existence of Lyme disease in Chile. Positive screening with negative confirmatory test suggests false positive non-specific reactivity or that local Borrelia are antigenically different compared to North American strains