The Voltage Sensor of Excitation-Contraction Coupling in Skeletal Muscle. Ion Dependence and Selectivity

Manifestations of excitation-contraction (EC) coupling of skeletal muscle were studied in the presence of metal ions of the alkaline and alkaline-earth groups in the extracellular medium. Single cut fibers of frog skeletal muscle were voltage clamped in a double Vaseline gap apparatus, and intramembrane charge movement and myoplasmic Ca2+ transients were simultaneously measured. In metal-free extracellular media both charge movement of the charge 1 type and Ca transients were suppressed. Under metal-free conditions the nonlinear charge distribution was the same in depolarized (holding potential of 0 mV) and normally polarized fibers (holding potentials between -80 and -90 mV). The manifestations of EC coupling recovered when ions of groups Ia and IIa of the periodic table were included in the extracellular solution; the extent of recovery depended on the ion species. These results are consistent with the idea that the voltage sensor of EC coupling has a binding site for metal cations--the priming site--that is essential for function. A state model of the voltage sensor in which metal ligands bind preferentially to the priming site when the sensor is in noninactivated states accounts for the results. This theory was used to derive the relative affinities of the various ions for the priming site from the magnitude of the EC coupling response. The selectivity sequence thus constructed is: Ca greater than Sr greater than Mg greater than Ba for group IIa cations and Li greater than Na greater than K greater than Rb greater than Cs for group Ia. Ca2+, the most effective of all ions tested, was 1,500-fold more effective than Na+. This selectivity sequence is qualitatively and quantitatively similar to that of the intrapore binding sites of the L-type cardiac Ca channel. This provides further evidence of molecular similarity between the voltage sensor and Ca channels

Estimation of Incoming Radiation From Extraterrestrial Radiation and Climatic Data

Average monthly values of incoming radiation, extraterrestrial radiation, sunshine, and sky cover frorn 32 climatological stations in the United States were used as a basis to develop radiation equations. Empirical relations between incoming radiation and more commonly available climatic and geographic variables, such as percent of relative sunshine, mean daily sky cover, station elevation and extraterrestrial radiation, were established using an empirical procedure used by Christiansen (1966, 1967) to compute his evaporation and evapotranspiration formulas. The reliability of the equations developed was deternlined by comparing the computed values of incoming radiation with measured values at Davis, California and for the Republic of Venezuela (Servicio de Meteorologia, 1965). For comparison, the formulas developed in this study and formulas developed by Fitzpatrick (1965), Black (1954), Glover and McCulloch (cited by Fitzpatrick, 1965) Morton (1965), and Bennett (1965) were applied to Venezuelan incoming solar radiation stations

Effect of water composition on catalytic reduction of nitrate

This work studies catalytic reduction of nitrate with bimetallic catalysts supported on γ-alumina (Pd-Sn/Al2O3 and Pd-In/Al2O3). Pd-Sn/Al2O3 yielded higher NO3− conversion and selectivity towards N2 than Pd-In/Al2O3 in synthetic water (deionized water with 100 mg/L NO3−). The Pd-Sn/Al2O3 catalyst showed highly stable behaviour, without signs of deactivation upon ten consecutive runs of 6 h each, where almost equal low selectivity to NH4+ (absence of NO2−) was maintained at high nearly constant nitrate conversion (≈ 90%). The presence of anions (Cl−, SO42− and HCO3−) in the reaction medium decreased NO3− conversion and the selectivity towards N2. Chloride showed a moderately negative effect at relatively low concentration. The effect of SO42− and HCO3− was more pronounced, being the second the most detrimental to the catalytic activity. The selectivity towards N2 was also negatively affected by the presence of those anions following the sequence HCO3− > SO42− > Cl−. However, the joint presence of Cl− or SO42− with HCO3− reduced the negative effect of the latter. The Pd-Sn/Al2O3 catalyst also showed high activity in NO3− reduction from drinking waters of weak mineralization, with a slightly increase of the selectivity towards NH4+ with respect to the obtained in deionized water with NO3− as the only anionThe authors wish to thank for the financial support the Spanish MINECO ( PID2019-108445RB-I00 ) and Comunidad de Madrid ( BIOTRES-CM , S2018/EMT-4344 ). I. Sanchis also thanks Comunidad de Madrid for award of a research grant ( PEJD-265 2017-PRE/AMB-4616

Protestas sociales en el Perú: consecuencias en la salud mental de la población

Sr. Editor, Desde mediados de diciembre del 2022 hasta parte de febrero del 2023 se desarrollaron en el Perú protestas sociales de gran magnitud que expresaron el reclamo de un sector de la población (1). Así, se registraron incidentes de violencia entre protestantes y las fuerzas del orden, bloqueo de carreteras, toma de aeropuertos, entre otros (2). Estos incidentes  produjeron la paralización de actividades económicas, sentimiento de inseguridad e incertidumbre social (1); y al 5 de febre-ro del 2023, 59 fallecidos y 1229 heridos (2). Además, millones de personas atestiguaron estos incidentes directa o indirectamente por medios de comunicación y redes sociales