Autonomic nervous system regulation of the sinoatrial cell depolarization rate: Unifying computational models

In the last years different computational models have been proposed to simulate the sinoatrial node cell (SANC) action potential. Also, there has been a great effort to model the heart regulation mechanism by the autonomic nervous system (ANS) through the sympathetic and parasympathetic pathways. Both computational models have tried to fit the rabbit and/or the guinea-pig experimental heart rate data with an increasing success. Thus, the aim of this work was to unify the available models that have been reported to study the heart rate behavior when the SANC is stimulated by using different frequency patterns. Our results contribute to the unification of part of the Scepanovic's model [1] (involved with second messengers dynamics and its influence over specific SANC ionic channels), and the SANC ionic channels computational model proposed by Severi et al. [2] in 2012. In this model unification we did refit some parameters, particularly, those related to the Hill functions in the dynamic modeling of phosphokinase and its effect on the ionic channels currents If and ICaL, and over the Pup, parameter that is related to the Ca(++) uptake by the sarcoplasmic reticulum. Also, we eliminated the neurotransmitter effect over the ionic current IKr that is not presented in the Severi's model. These modifications were enough to successfully reproduce the heart rate experimental recordings under acetylcholine (Ach) or norepinephrine (NE) for independent stimulation: Ach 10 nM stimulation showed a 21.54% action potential shift compared with the 20% reported for experimental recordings; Isoprenaline 1 μM, also displayed a depolarization increased rate of 29.3%, compared with the experimental data of 28.2%. Furthermore, we were able to reproduce the guinea-pig experimental heart rate recordings, when the SANC model was vagal stimulated by using a 2 Hz, 10 Hz and 20 Hz frequency for 10 seconds and the experimental heart rate data for a sympathetic stimulation of 10 Hz frequency for 10 seconds.

Effect of sodium deprivation on contraction and charge movement in frog skeletal muscle fibres

Measurements of isometric tension were performed in single twitch skeletal muscle fibres and the effect of extracellular Na+ removal on contraction was investigated. Na+ withdrawal brought about an increase in the amplitude of K+ contractures and their time course became faster. The potentiation of K+ contractures depended strongly on extracellular Ca2+ and developed slowly following an exponential time course with a time constant of approximately 8 min. Removal of extracellular Na+ greatly increased the amplitude of caffeine contractures and lowered its threshold: caffeine (0.5 mM) had no effect on resting tension in Ringer's but produced contractures in Na(+)-free solutions. Intramembrane charge movement (charge 1) was monitored in contracting voltage-clamped segments of frog skeletal muscle fibres using the triple-Vaseline-gap technique. Movement of charge 1 did not depend on the presence of extracellular Na+. However, the mechanical threshold decreased by approximately 10 mV at several pulse durations and the charge which produced just detectable contractions decreased by approximately 5 nC microF-1 in the absence of extracellular Na+. Intracellular heparin (40 mg ml-1) increased the mechanical threshold by approximately 20 mV without affecting the movement of charge 1. The effect of Na(+)-free solutions on the mechanical threshold was additive to that of heparin. It is concluded that the effects of Na(+)-withdrawal on contraction take place at a location beyond the voltage sensor of excitation-contraction coupling.

[Agreement among observers in the classification of acute leukemias]

This study was carried out to establish the level of concordance between two observers from two different health institutions in Mexico City, in the diagnosis of acute leukemias and their different varieties. We studied 73 consecutive cases of adults with these diseases. Each one of the two observers established their diagnosis on two occasions at least 15 days apart. They first made their diagnosis taking as a base the neoplastic cells morphology in bone marrow smears, and after that, with morphology plus specific cytochemistry. The outcomes of the two observers were also compared with the official diagnosis. Kappa test was performed to know interobserver and intraobserver concordance. The kappa values for the diagnosis myeloid/lymphoid were found among the highest (51 to 91). Weighted kappa was also applied to know the level of concordance in the diagnosis of the different varieties of acute leukemia, myeloid and lymphoid. In these cases the weighted kappa values were lower compared with the previous values (lymphoid, from 47 to 82; myeloid, from 30 to 66). Cytochemistry paradoxically was a confusing factor when it was used: in these cases the kappa values were lower (32 to 84) than morphology alone (39 to 91). The outcomes showed the subjective level in the diagnosis of the myeloid subtypes was more important in them than in the lymphoid subtypes.