Low pO2 selectively inhibits K channel activity in chemoreceptor cells of the mammalian carotid body

Producción CientíficaThe hypothesis that changes in environmental 02 tension (pOi) could affect the ionic conductances of dissociated type I cells of the carotid body was tested. Cells were subjected to whole-cell patch clamp and ionic currents were recorded in a control solution with normal pO 2 (pO~ = 150 mmHg) and 3-5 min after exposure to the same solution with a lower pO,. Na and Ca currents were unaffected by lowering pO, to 10 mmHg, however, in all cells studied (n = 42) exposure to hypoxia produced a reversible reduction of the K current. In 14 cells exposed to a pO 2 of 10 mmHg peak K current amplitude decreased to 35 +_ 8% of the control value. The effect of low pO2 was independent of the internal Ca 2+ concentration and was observed in the absence of internal exogenous nucleotides. Inhibition of K channel activity by hypoxia is a graded phenomenon and in the range between 70 and 120 mmHg, which includes normal pO, values in arterial blood, it is directly correlated with pO 2 levels. Low pO2 appeared to slow down the activation time course of the K current but deactivation kinetics seemed to be unaltered. Type I cells subjected to current clamp generate large Na- and Cadependent action potentials repetitively. Exposure to low pO~ produces a 4-10 mV increase in the action potential amplitude and a faster depolarization rate of pacemaker potentials, which leads to an increase in the firing frequency. Repolarization rate of individual action potentials is, however, unaffected, or slightly increased. The selective inhibition of K channel activity by low pO, is a phenomenon without precedents in the literature that explains the chemoreceptive properties of type I cells. The nature of the interaction of molecular O, with the K channel protein is unknown, however, it is argued that a hemoglobin-like O, sensor, perhaps coupled to a G protein, could be involved

Ionic currents in dispersed chemoreceptor cells of the mammalian carotid body

Producción CientíficaIonic currents of enzymatically dispersed type 1 and type 11 cells of the carotid body have been studied using the whole cell variant of the patch-clamp technique. Type 11 cells only have a tiny, slowly activating outward potassium cur­ rent. By contrast, in every type 1 chemoreceptor cell studied we found (a) sodium, (b) calcium, and (e) potassium currents. (a) The sodium current has a fast activation time course and an activation threshold at --40 mV. At ali voltages inactivation follows a single exponential time course. The time constant of inactivation is 0.67 ms at O mV. Half steady state inactivation occurs at a membrane potential of --50 mV. (b) The calcium current is almost totally abolished when most of the extemal calcium is replaced by magnesium. The activation threshold of this cur­ rent is at --40 mV and at O mV it reaches a peak amplitude in 6-8 ms. The calcium current inactivates very slowly and only decreases to 27% of the maximal value at the end of 300-ms pulses to 40 mV. The calcium current was about two times larger when barium ions were used as charge carriers instead of calcium ions. Barium ions also shifted 15-20 mV toward negative voltages the conductance vs. voltage curve. Deactivation kinetics of the calcium current follows a biphasic time course well fitted by the sum of two exponentials. At -80 mV the slow com­ ponent has a time constant of 1.3 ± 0.4 ms whereas the fast component, with an amplitude about 20 times larger than the slow component, has a time constant of 0.16 ± 0.03 ms. These results suggest that type 1 cells have predominantly fast deactivating calcium channels. The slow component of the tails may represent the activity of a small population of slowly deactivating calcium channels, although other possibilities are considered. (e) Potassium current seems to be mainly due to the activity of voltage-dependent potassium channels, but a small percentage of calcium-activated channels may also exist. This current activates slowly, reaches a peak amplitude in 5-1O ms, and thereafter slowly inactivates. Inactivation is almost complete in 250-300 ms. The potassium current is reversibly blocked by tetraeth­ ylammonium. Under current-clamp conditions type I cells can spontaneously fire large action potentials

Low pO2 selectively inhibits K channel activity in chemoreceptor cells of the mammalian carotid body

The hypothesis that changes in environmental O2 tension (pO2) could affect the ionic conductances of dissociated type I cells of the carotid body was tested. Cells were subjected to whole-cell patch clamp and ionic currents were recorded in a control solution with normal pO2 (pO2 = 150 mmHg) and 3-5 min after exposure to the same solution with a lower pO2. Na and Ca currents were unaffected by lowering pO2 to 10 mmHg, however, in all cells studied (n = 42) exposure to hypoxia produced a reversible reduction of the K current. In 14 cells exposed to a pO2 of 10 mmHg peak K current amplitude decreased to 35 +/- 8% of the control value. The effect of low pO2 was independent of the internal Ca2+ concentration and was observed in the absence of internal exogenous nucleotides. Inhibition of K channel activity by hypoxia is a graded phenomenon and in the range between 70 and 120 mmHg, which includes normal pO2 values in arterial blood, it is directly correlated with pO2 levels. Low pO2 appeared to slow down the activation time course of the K current but deactivation kinetics seemed to be unaltered. Type I cells subjected to current clamp generate large Na- and Ca-dependent action potentials repetitively. Exposure to low pO2 produces a 4-10 mV increase in the action potential amplitude and a faster depolarization rate of pacemaker potentials, which leads to an increase in the firing frequency. Repolarization rate of individual action potentials is, however, unaffected, or slightly increased. The selective inhibition of K channel activity by low pO2 is a phenomenon without precedents in the literature that explains the chemoreceptive properties of type I cells. The nature of the interaction of molecular O2 with the K channel protein is unknown, however, it is argued that a hemoglobin-like O2 sensor, perhaps coupled to a G protein, could be involved

Ionic currents in dispersed chemoreceptor cells of the mammalian carotid body

Ionic currents of enzymatically dispersed type I and type II cells of the carotid body have been studied using the whole cell variant of the patch-clamp technique. Type II cells only have a tiny, slowly activating outward potassium current. By contrast, in every type I chemoreceptor cell studied we found (a) sodium, (b) calcium, and (c) potassium currents. (a) The sodium current has a fast activation time course and an activation threshold at approximately -40 mV. At all voltages inactivation follows a single exponential time course. The time constant of inactivation is 0.67 ms at 0 mV. Half steady state inactivation occurs at a membrane potential of approximately -50 mV. (b) The calcium current is almost totally abolished when most of the external calcium is replaced by magnesium. The activation threshold of this current is at approximately -40 mV and at 0 mV it reaches a peak amplitude in 6-8 ms. The calcium current inactivates very slowly and only decreases to 27% of the maximal value at the end of 300-ms pulses to 40 mV. The calcium current was about two times larger when barium ions were used as charge carriers instead of calcium ions. Barium ions also shifted 15-20 mV toward negative voltages the conductance vs. voltage curve. Deactivation kinetics of the calcium current follows a biphasic time course well fitted by the sum of two exponentials. At -80 mV the slow component has a time constant of 1.3 +/- 0.4 ms whereas the fast component, with an amplitude about 20 times larger than the slow component, has a time constant of 0.16 +/- 0.03 ms. These results suggest that type I cells have predominantly fast deactivating calcium channels. The slow component of the tails may represent the activity of a small population of slowly deactivating calcium channels, although other possibilities are considered. (c) Potassium current seems to be mainly due to the activity of voltage-dependent potassium channels, but a small percentage of calcium-activated channels may also exist. This current activates slowly, reaches a peak amplitude in 5-10 ms, and thereafter slowly inactivates. Inactivation is almost complete in 250-300 ms. The potassium current is reversibly blocked by tetraethylammonium. Under current-clamp conditions type I cells can spontaneously fire large action potentials. These results indicate that type I cells are excitable and have a variety of ionic conductances. We suggest a possible participation of these conductances in chemoreception

Physiological characteristics of libero and central volleyball players

The aim of this study is to determine the intensity of effort in competition of the libero and central players by measuring heart rate and blood lactate. A sample of 30 players from 10 teams was used. Heart rate was measured by telemetry during the matches. Blood samples were obtained when there were substitutions for the players and about 300 samples were taken. Significant differences were observed in mean and maximal heart rate values between the central players and the libero (p<0.01). Mean and maximal heart rate values tended to decrease in the last sets in all the positions analysed. Higher levels have been observed in the libero when the set is lost than when it is won. (p<0.01). With regard to blood lactate, significant differences were found in mean values between the two central players and the libero (p<0.01). It was observed that 40.9% of all the blood lactate concentrations, regardless of the position, corresponded to values higher than 4 mmol•l-1, and 2.8% were above 8 mmol•l-1. These values are far higher than those found in earlier studies

Study about game continuity in children´s volleyball

El propósito del estudio fue apoyar con resultados el debate por la necesidad de adaptar el reglamento en las categorías menores. El único cambio dado actualmente en el ámbito español, con respecto a las normas internacionales, es la supresión del líbero en la categoría estudiada. Se analizaron datos del único campeonato de España en el que se permitió su participación. Los resultados no se muestran positivos desde una de las variables consideradas con más valor formativo: la continuidad. Del mismo modo, el ataque de primer tiempo, acción crítica debatida por su especialización temprana, da una relación positiva con el criterio focal estudiado. Resultados similares se encontraron en factores contextuales como el set y la fase de juego (saque o recepción).The aim of this study was to give information for debate about the needs to adaptation the game rules in children´s volleyball. Only there is one change between international and children´s rules in Spain. We analysed data from the only championship played in Spain when it was allowed to play with “libero”. Results don´t show a positive dependence with one of the most important factors in the player’s development: continuity. First tempo is other critical factor in the debate about early specialitation. There´s no a lot presence in this case, but it also show a positive dependence with continuity. Other contextual factors like set match playing or the different match phase (serve or reception), are in relationship with continuity

Volleyball spanish child. Study level of participation in the game

El objetivo del estudio fue determinar qué factores inciden sobre el nivel de participación de los jugadores de equipos infantiles de voleibol masculino. Se analizaron número de transiciones hacia el campo contrario, la continuidad, forma de culminación del punto y resultado de éste. El estudió se centró en el Campeonato de España Escolar masculino del año 2002, en torno a las edades de 12- 14 años, mediante un diseño de investigación sincrónico simétrico y multidimensional. El número de transiciones hacia el campo contrario y la continuidad mostraron relación directa con el criterio focal del estudio no produciéndose, sin embargo, significación estadística entre un incremento de la participación con una mayor probabilidad de culminar los puntos en remate ni con una consecución de mayor cantidad de puntos. Podemos concluir que en esta categoría predomina un estilo de juego especializado y jerarquizado donde los mejores jugadores tienen mayor participación en el juego.The aim of this study was to establish the factors which affect the level of participation among players of different youth male volleyball teams. Number of transitions, continuity, point finalization and its result, were analyzed. The study was focused on the 2002 Male under 14 Scholar Spanish Championship, through a synchronic, symmetric and multidimensional investigation design. The Number of transitions to the other court and continuity had a straight relation with the focus of the research; however, there is no statistical signification between the increased participation with more likely of completing finish points and achieving a most points. We concluded that it can be considered that this volleyball category is characterized by the existence of a specialized and hierarchical game style, in which the best players show a highest level of involvement during the game

Non-volatile analysis in fruits by laser resonant ionization spectrometry: application to resveratrol (3,5,4 -trihydroxystilbene) in grapes

Applied Physics B Lasers and Optics, vol.71A laser desorption (LD) coupled with resonanceenhanced multiphoton ionisation (REMPI) and time-of-flight mass spectrometry (TOFMS) technique for non-volatile trace analysis compounds is presented. Essential features are: (a)an enhanced desorption yield due to the mixing of metal powder with the analyte in the sample preparation, (b) a high resolution, great sensitivity and low detection limit due to laser resonant ionisation and mass spectrometry detection. Application to resveratrol content in grapes demonstrated the capability of the analytical method with a sensitivity of 0.2 pg per single laser shot and a detection limit of 5 ppb