Calcium-osmolality Interaction In The Inotropic Response Of Isolated Rat Atria To Increased Sodium Concentration.

The effects of osmolality (300 and 450 mOsm/l) and external calcium concentration ([Ca2+]o: 0.87, 1.13, 1.47 and 1.92 mM) on the inotropic response of isolated rat left atria to an increase of 97.8 mM in extracellular sodium concentration ([Na+]o) were studied. The evoked tensions developed during 30 min after the exposure to increased [Na+]o increased with increasing [Ca2+]o. In iso-osmotic solutions, tension was lower than in hyperosmotic solutions when [Ca2+]o was 0.87 and 1.13 mM, but not for higher [Ca2+]o, revealing a Ca2(+)-osmolality interaction in the determination of the inotropic response.22680781

Effect Of Hyperosmolality On The Sensitivity Of Right And Left Atria Of The Rat To Noradrenaline.

This study analyzes the effects of hyperosmotic solutions on the sensitivity of the rat isolated right and left atria to the chronotropic and inotropic effects of noradrenaline (NA), respectively. Hyperosmotic NaCl solution caused subsensitivity to both effects of NA (pD2 values for NA, right atria: control 7.42 +/- 0.06, NaCl 6.83 +/- 0.18, P less than 0.05; left atria: control 7.67 +/- 0.22, NaCl 6.61 +/- 0.18, P less than 0.05). Hyperosmotic sucrose solution produced a similar effect in right atria (pD2 NA: 6.96 +/- 0.17, P less than 0.05), whereas in left atria it depressed the maximum inotropic response to NA by about 80%. All changes, except that of maximum inotropic response, were abolished following combined pretreatment with 6-hydroxydopamine, phenoxybenzamine, atropine and imipramine. These data suggest that the noradrenergic subsensitivity induced in atrial tissue by hyperosmolality is probably not due to changes of beta-adrenoceptor function and/or coupling of these receptors to the effector mechanisms.2281005100

Determination Of The Vectorelectrogram In Isolated Rat Atria: Application To The Study Of Arrhythmias.

Atrial tachyarrhythmias, the most frequent type of cardiac arrhythmia, are associated with increased stroke risk. Reentry and focal activity are considered as the main mechanisms underlying this dysfunction. In this study, we describe determination of the vectorelectrogram in isolated rat atria as a means to distinguish different patterns of electrical propagation. In all studied right atria beating at sinus rhythm, the mean electric vector (MEV) trajectory was clockwise, and each cycle was preceded by electric diastole (null MEV), either in the absence or presence of muscarinic cholinergic or beta-adrenergic receptor stimulation. During cholinergic tachyarrhythmia (induced by high-rate electric stimulation in both atria, plus exposure to carbachol in left atria), vector loops were ellipsoidal and stable, with variable direction, and did not cross the origin, which is consistent with reentrant activation and with findings obtained in vivo by other authors. In contrast, during spontaneous activity induced by rapid pacing in isoproterenol-exposed left atria, vector loops were similar to those in right atria at sinus rhythm, thus suggestive of focal activity. It is concluded that the vectorelectrogram approach allows discrimination of different patterns of propagation during arrhythmia in isolated atria and may be useful for high-output tests of pro- and anti-arrhythmic compounds.30111281129

Influence Of The Kcl Concentration On Rat Sinus Node Recovery Time In Vitro.

The influence of changes in the KCl concentration of the bath fluid ([KCl]o) on the corrected sinus node recovery time (CSNRT) was studied using the continuous pacing method (M1) and the method of stimulation with premature pulses (M2). M1 and M2 were compared in Krebs-Henseleit solution containing normal (4.6 mM), low (3.1 mM, LoKCl) and high (6.1 mM, HiKCl) [KCl]o. The results revealed that HiKCl increased CSNRT (P less than 0.01) and changed the prematurity-CSNRT relationship (P less than 0.01), whereas LoKCl did not change CSNRT. M1 and M2 were different (P less than 0.01) regardless of [KCl]o, except for pacing intervals near the spontaneous cycle length.22680380

Influence Of Stimulatory Parameters On Sinus Node Recovery Time: An In Vitro Study.

The effects of pacing frequency, overdrive duration and stimulus amplitude on the sinus node recovery time (SNRT) were studied in the isolated right atrium of the rat. A positive relationship between pacing frequency and the SNRT was observed, whereas overdrive duration and stimulus amplitude did not affect SNRT. There was no significant interaction among the factors studied. The effect of frequency upon SNRT probably does not involve neurotransmitter release due to stimulation, since in vitro pretreatment with atropine plus propranolol does change the SNRT-frequency relation.2151079108

Rupture of blood clots: Mechanics and pathophysiology

© 2020 The Authors. Fibrin is the three-dimensional mechanical scaffold of protective blood clots that stop bleeding and pathological thrombi that obstruct blood vessels. Fibrin must be mechanically tough to withstand rupture, after which life-threatening pieces (thrombotic emboli) are carried downstream by blood flow. Despite multiple studies on fibrin viscoelasticity, mechanisms of fibrin rupture remain unknown. Here, we examined mechanically and structurally the strain-driven rupture of human blood plasma-derived fibrin clots where clotting was triggered with tissue factor. Toughness, i.e., resistance to rupture, quantified by the critical energy release rate (a measure of the propensity for clot embolization) of physiologically relevant fibrin gels was determined to be 7.6 ± 0.45 J/m2. Finite element (FE) simulations using fibrin material models that account for forced protein unfolding independently supported this measured toughness and showed that breaking of fibers ahead the crack at a critical stretch is the mechanism of rupture of blood clots, including thrombotic embolization