TMEM16 proteins: the long awaited calcium-activated chloride channels?

Currents mediated by calcium-activated chloride channels (CaCCs), observed for the first time in Xenopus oocytes, have been recorded in many cells and tissues ranging from different types of neurons to epithelial and muscle cells. CaCCs play a role in the regulation of excitability in neurons including sensory receptors. In addition, they are crucial mediators of chloride movements in epithelial cells where their activity regulates electrolyte and fluid transport. The roles of CaCCs, particularly in epithelia, are briefly reviewed with emphasis on their function in secretory epithelia. The recent identification by three independent groups, using different strategies, of TMEM16A as the molecular counterpart of the CaCC is discussed. TMEM16A is part of a family that has 10 other members in mice. The discovery of the potential TMEM16 anion channel activity opens the way for the molecular investigation of the role of these anion channels in specific cells and in organ physiology and pathophysiology. The identification of TMEM16A protein as a CaCC chloride channel molecule represents a great triumph of scientific perseverance and ingenuity. The varied approaches used by the three independent research groups also augur well for the solidity of the discovery.

Toxicidad aguda de altas dosis de metotrexato en el tratamiento de leucemia linfoblástica aguda en niños / Acute toxicity of high close of Methotrexae in children with acute lymphoblastic leukemia

El objetivo de ese estudio fue evaluar y comparar la aparición de efectos adversos agudos luego de la infusión de metotrexato (MTX), citostático incluido en alas dosis en 2 diferentes protocolos (2g. vs. 5g/m2 por ciclo), utilizados durante la fase M del tratamiento de las leucemias linfoblásticas agudas (LLA) en el paciente pediátrico. Sesenta y seis pacientes que recibieron 264 ciclos de quimioterapia con altas dosis de MTX, fueron estudiados entre enero de 1995 y febrero de 1997. Todos ellos tenían el diagnóstico de LLA de riesgo estándar e intermedio, estaban en remisión completa y habián recibido anteriormente el protocolo I. Se anlizaron 2 tratamiento: el gurpo A) 132 ciclos con MTX a razón de 2g/m2/ciclo (n=32); grupo B 136 cilos con MTX a razón de 5g/m2/ciclo (n=34). Todos los pacientes recibieron 4 infusiones de MTX (1/10 de la dosis en 30´ y 9/10 de la dosis en el resto de las 24 hs.), con hidratación a 3000 ml/m2/día y alcalinización urinaria, en forma bimensual, junto a una punción lumbar con mediación intratecal (Profilaxis para evitar compromiso del sistema nervioso central) y 6-mercaptopurina oral diariamente durante el ciclo. No se observaron diferencias estadísticas significativas en relación a toxicidad hematológica severa: en 42 cukis (32.81 por ciento) en el grupo A y 44 cilcos (32.35 por ciento) en el grupo B; z=0.042: p=0.967. Sin embargo, la aparición de mucositis moderada y severa y valores elevados de las enzimas hepáticas se observaron con mayor frecuencia en el grupo B, mostrando una diferencia estadísticamente significativa. En nuestro estudio, no se observaron valores anormales de creatinina sérica. No hubo impacto sobre variaciones en el peso corporal en ambos protocolos. Concluimos que la dosis de MTX no influyó sobre la aparición de toxicidad hematológica, pero si sobre la aparición de efectos adversos en el tracto gastrointestinal y la función hepática.

Histopathological analysis of rat mesentery as a method for evaluating neutrophil migration: differential effects of dexamethasone and pertussis toxin

In the present study, histopathological analysis of rat mesentery was used to quantify the effect of two anti-inflammatory agents, dexamethasone (Dex) and pertussis toxin (Ptx), on leukocyte migration. The intravenous injection of Dex (1 mg/kg) and Ptx (1,200 ng) 1 h prior to the intraperitoneal injection of the inflammatory stimuli lipopolysaccharide (LPS) or formyl-methionyl-leucyl-phenylalanine (fMLP) significantly reduced the neutrophil diapedesis (LPS: Ptx = 0.86 ñ 0.19 and Dex = 0.35 ñ 0.13 vs saline (S) = 2.85 ñ 0.59; fMLP: Ptx = 0.43 ñ 0.09 and Dex 0.01 ñ 0.01 vs S = 1.08 ñ 0.15 neutrophil diapedesis/field) and infiltration (LPS: Ptx = 6.29 ñ 1.4 and Dex = 3.06 ñ 0.76 vs S = 15.94 ñ 3.97; fMLP: Ptx = 3.85 ñ 0.56 and Dex = 0.40 ñ 0.16 vs S = 7.15 ñ 1.17 neutrophils/field) induced by the two agonists in the rat mesentery. The inhibitory effect of Dex and Ptx was clearly visible in the fields nearest the venule (up to 200 µm), demonstrating that these anti-inflammatory agents act preferentially in the transmigration of neutrophils from the vascular lumen into the interstitial space, but not in cell movement in response to a haptotactic gradient. The mesentery of rats pretreated with Dex showed a decreased number of neutrophils within the venules (LPS: Dex = 1.50 ñ 0.38 vs S = 4.20 ñ 1.01; fMLP: Dex = 0.25 ñ 0.11 vs S = 2.20 ñ 0.34 neutrophils in the lumen/field), suggesting that this inhibitor may be acting at a step that precedes neutrophil arrival in the inflamed tissue. In contrast to that observed with Dex treatment, the number of neutrophils found in mesenteric venules was significantly elevated in animals pretreated with Ptx (LPS: Ptx = 9.85 ñ 2.25 vs S = 4.20 ñ 1.01; fMLP: Ptx = 4.66 ñ 1.24 vs S = 2.20 ñ 0.34 neutrophils in the lumen/field). This discrepancy shows that Ptx and Dex act via different mechanisms and suggests that Ptx prevents locomotion of neutrophils from the vascular lumen to the interstitial space. In conclusion, the method described here is useful for quantifying the inflammatory and anti-inflammatory effect of different substances. The advantage of this histopathological approach is that it provides additional information about the steps involved in leucocyte migration.

The Blue infarct: a simple method for the quantification of myocardial damage in the rat

Evans blue dye was injected in vitro rats 24 h before left coronary occlusion (CO) and the dye content extracted with formamide was estimated after various time intervals in the 1) right ventricle, 2) left ventricle above the ligature and 3) the rest of the left ventricle. There was no difference between portion 1 and 2 but portion 3 showed a progressive increase in dye content (2 to 3 fold) up to 24 h after CO. This result indicates that either the infarcted area possesses collateral circulation or a continuous blood backflow occurred. Dexamethasone (0.5 mg/kg) but not indomethacin (2 mg/kg) or BW755C (10 mg/kg) abolished extravasation of the dye