Responses to Norepinephrine of Normal and "Ischemic" Canine Purkinje Fibers are Consistent with Activation of Different α1-Receptor Subtypes

α₁-Receptor Subtype Stimulation of Purkinje Fibers. Introduction: Previously we found that WB4101 (WB) 10^-7 M competitively blocks three α₁-adrenergic receptor-effector responses: the increase in normal automaticity occurring in Purkinje fibers (PF) at high membrane potentials: the increase in abnormal automaticity occurring in PF at depolarized membrane potentials; and the prolongation of PF action potential duration. These observations are consistent with two different hypotheses: (1) WB blocks a single α₁-receptor subtype, which subserves different effector pathways; and (2) WB blocks different receptor subtypes, eacb of which subserves an independent patbway. The aim of this study was to test both hypotheses. Methods and Results: We used standard microelectrode techniques to study the concentration-dependent actions of three α₁-adrenoreceptor blockers (WB (α_1A?α_1D], 5-methylurapidil [5-MU] [α_1A, ?α_1D], and UK52,046 [nonselective]) on norepinephrine (NK) effects in normal PF and in PF depolarized with a simulated ischemic solution ([K⁺]_o= 10 mM; pO₂ < 20 mmHg; pH 6.8; maximum diastolic potential -60 ± 1 mV). In normally polarized PF, concentration-dependent actions of all blockers on both the positive cbronotropic response and the prolongation of action potential duration completely coincide. In contrast, the response to NE of abnormal automaticity in “ischemic” PF differs from normals: there is a bigh sensitivity to WB and 5-MU and no response to UK52,046. Conclusions: (1) A single receptor subtype appears responsible for botb the α₁-induced prolongation of repolarization and the positive chronotropic effect in normal PF. (2) Two different receptor subtypes may be responsible for the α₁-induced effects on automaticity in normal and ischemic fibers. It is likely that the latter one is α_1A, and that consideration of antiarrhythmic therapy with α₁-adrenergic blockers should focus on this subtype as a potential target.     

磁耦合驱动搏动式血泵的可行性研究

目的提出一种磁耦合驱动搏动式血泵结构并验证其可行性。方法基于磁场传递往复作用力模型以及推拉互挽式结构设计磁耦合驱动搏动血泵,通过建立磁力驱动模型,计算耦合力大小,制作样机并对样机进行体外循环模拟试验,获得压力和流量实验数据。结果采用生理盐水作为循环介质,固定后负荷,增加前负荷,血泵输出量减少,没有明显线性趋势;固定前负荷,增加后负荷,血泵输出量减少,且具有一定线性趋势。设置驱动频率为75次/min时,调节前、后负荷改变范围分别为0.665~3.990 k Pa(5~30 mm Hg)和5.320~11.970 k Pa(5~30 mm Hg),可使输出量在保证线性关系条件下达到2.0~3.1 L/min。结论该搏动式血泵流体力学特性基本满足体外膜肺循环的需要,仍需进一步研究和改进;研究结果具有重要的应用前景,尤其对替代目前临床体外膜肺氧合设备的血泵装置具有重要意义。     

Influence of metabolic inhibition by NaCN on electrical and mechanical activities of frog atrial fibers: Studies using current and voltage clamp

Voltage clamp experiments have documented that after 10 min NaCN treatment: (1) there is a reduction in both action potential duration and plateau amplitude associated with a reduction in the contractile strength; (2) in Ringer tetrodotoxin there is a marked reduction in the magnitude of the slow inward current and the corresponding tension; (3) there is a negative shift in the reversal potential of the slow inward current.In previous work it was suggested that during metabolic inhibition the lack of high energy compounds leads to an increase in the intracellular free Ca²⁺ concentration, thereby decreasing the Ca²⁺ driving force. However, the present study has shown that excess Ca²⁺ in the bathing solution was unable to increase the slow inward current amplitude during NaCN treatment, although the $\text{I}\text{V}$ relationship showed a restoration of the Ca²⁺ driving force. On the other hand the application of 10^?7m adrenaline during poisoning induced a rapid increase in both the slow inward current and the phasic contraction amplitude. It is concluded that NaCN reduces the slow inward current and the corresponding tension, decreasing both Ca²⁺ driving force and slow channel conductance. The marked increase in both slow inward current and phasic component of contraction with adrenaline suggests that under these conditions cyclic AMP is made available in spite of metabolic inhibition, thereby preventing the increase of internal free Ca²⁺ concentration, and also increasing the slow channel conductance.     

A review of novel technologies and techniques associated with identification of bloodstream infection etiologies and rapid antimicrobial genotypic and quantitative phenotypic determination

Introduction: The antimicrobial aspect of management of patients with blood stream infections (BSI) and sepsis is time critical. In an era of increasing antimicrobial resistance, rapid detection and identification of bacteria with antimicrobial susceptibility is crucial to direct therapy early in the course of illness. Molecular techniques offer a potential solution to this.

Areas covered: In the present review the authors have discussed a number of novel solutions utilizing a variety of molecular techniques for pathogen detection, identification and antimicrobial susceptibility. The review is not designed to be an exhaustive literature review covering all diagnostic solutions ever developed, instead the authors have focused on what they have had experience using, evaluating or currently view as new and exciting with potential to revolutionize BSI diagnosis.

The authors searched PubMed (Medline) and Google Scholar with terms: BSI, Bacteraemia, Candidaemia, Diagnostics, AST, Rapid, AMR, Novel and Blood Culture. The authors attended recent clinical microbiology technology congresses.

Expert commentary: There are multiple exciting novel technologies at differing stages of development with potential to revolutionize diagnosis of BSI. More work is needed as well as a standardized assessment of different platforms in order to better understand the clinical and financial impacts these will have in clinical microbiology laboratories.     

Electromechanical time course in frog ventricle: Manipulation of calcium level during voltage clamp

Extracellular calcium concentration was rapidly altered in the “diastolic” interval between two contractions, and also during the time course of a single 10 s clamp pulse. The results strongly suggest that contraction of frog ventricular muscle is largely determined by a continuous, voltage-dependent influx of calcium into the cell, with little or no contribution from mechanisms involving release of calcium from intracellular stores. In addition, contraction can be graded, as a rapid response to alterations in extracellular calcium concentration.     

T-type Ca2+ current contribution to Ca2+-induced Ca2+ release in developing myocardium

In normal adult-ventricular myocardium, Ca2+-induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR) is activated via Ca2+ entry through L-type Ca2+ channels. However, embryonic-ventricular myocytes have a prominent T-type Ca2+ current (ICa,T). In this study, the contribution of ICa,T to CICR was determined in chick-ventricular development. Electrically stimulated Ca2+ transients were examined in myocytes loaded with fura-2 and Ca2+ currents with perforated patch-clamp. The results show that the magnitudes of the Ca2+ transient, L-type Ca2+ current (ICa,L) and ICa,T, decline with development with the majority of the decline of transients and ICa,L occurring between embryonic day (ED) 5 and 11. Compared to controls, the magnitude of the Ca2+ transient in the presence of nifedipine was reduced by 41% at ED5, 77% at ED11, and 78% at ED15. These results demonstrated that the overall contribution of ICa,T to the transient was greatest at ED5, while ICa,L was predominate at ED11 and 15. This indicated a decline in the contribution of ICa,T to the Ca2+ transient with development. Nifedipine plus caffeine was added to deplete the SR of Ca2+ and eliminate the occurrence of CICR due to ICa,T. Under these conditions, the transients were further reduced at all three developmental ages, which indicated that a portion of the Ca2+ transients present after just nifedipine addition was due to CICR stimulated by ICa,T. These results indicate that Ca2+ entry via T-type channels plays a significant role in excitation-contraction coupling in the developing heart that includes stimulation of CICR.     

Circadian urinary 6-sulphatoxymelatonin, cortisol excretion and locomotor activity in airline pilots during transmeridian flights

Airline pilots divided into two groups of age (over and under 50 years) were studied before, during and after westbound (Madrid-Mexico City-Madrid, n = 12) and eastbound (Madrid-Tokyo-Madrid, n = 21) flights. A group of 10 age-matched people staying in Madrid were submitted to the same tests and served as a control group. Changes in urinary 6-sulphatoxymelatonin (6-aMTs) and free cortisol excretion (determined in 6-hr intervals) were measured by radioimmunoassay. Using wrist actigraphy, the circadian locomotor activity rhythm (LAR) was also monitored. Maximal baseline excretion of 6-aMTs occurred between 00:00 and 12:00 hr and maximal excretion of cortisol took place between 6:00 and 12:00 hr in the control group. Analysed globally, older pilots exhibited significantly lower values of 6-aMTs than younger ones. In both flight directions, pilots maintained the pattern of excretion of 6-aMTs, corresponding to baseline. The return flight to Madrid from Mexico and Tokyo coincided with a maximum in 6-aMTs excretion. Pilots kept the cortisol pattern found in the control group, with those over 50 years of age exhibiting significantly lower cortisol values than the younger ones. A 7-hr delay in acrophase of LAR after 2 days in Mexico City was found after cosinor analysis, and similar pre-flight values were found after returning to Madrid. An 8-9-hr acrophase advance of LAR was observed after arriving in Tokyo, with acrophase on the post-return flight day still being advanced 3 4 hr as compared to pre-flight values. Decreases in the amplitude of LAR in older pilots were found at Mexico City, as well as at Tokyo stopover and on post-flight day. Data confirm the occurrence of internal desynchronization in airline crewmembers after transmeridian flights.     

Treatment of experimental meconium aspiration syndrome with surfactant lung lavage and conventional vs. asymmetric high-frequency jet ventilation

Respiratory failure caused by meconium aspiration requires combined strategies. We hypothesized that surfactant lung lavage with asymmetric high-frequency jet ventilation (AHFJV) can increase the removal of meconium and improve lung function. During conventional ventilation (CV), a suspension of human meconium (25 mg/ml, 4 ml/kg) was instilled into the tracheal tube of anesthetized rabbits to cause respiratory failure. Animals were then divided into four groups: saline lavage + CV (Sal-CV), surfactant lavage + CV (Surf-CV), saline lavage + HFJV (Sal-HFJV), and surfactant lavage + HFJV (Surf-HFJV). Lung lavage (10 ml/kg in 3 portions) was performed with diluted surfactant (Curosurf, 100 mg of phospholipids/kg) or saline during CV (frequency (f), 30/min; inspiration time (Ti), 50%) or AHFJV (f, 300/min; Ti, 70%). Animals were ventilated for an additional hour with either CV or HFJV (Ti, 50%). Surfactant lavage with both CV and AHFJV removed more meconium than saline lavage. However, the highest removal was found in the Surf-HFJV group vs. all other groups (P < 0.05). The oxygenation index decreased after surfactant lavage in both groups compared to controls (P < 0.001), and more prominently in the Surf-CV group. Elimination of CO(2) was significantly higher in the Surf-HFJV group vs. all other groups (P < 0.05). The ventilation efficiency index increased after lavage in both surfactant groups vs. saline controls (P < 0.05). Dynamic lung-thorax compliance gradually increased, and right-to-left pulmonary shunts decreased in both surfactant groups vs. saline controls after lavage (P < 0.05). Combination of surfactant lavage with both CV and AHFJV was beneficial in rabbits with meconium aspiration syndrome. While AHFJV was more effective in the removal of meconium, CV had a more favorable effect on lung function in the postlavage period.     

Opposed hemodynamic responses following increased excitation and parvalbumin-based inhibition

Understanding cellular contributions to hemodynamic activity is essential for interpreting blood-based brain mapping signals. Optogenetic studies examining cell-specific influences on local hemodynamics have reported that excitatory activity results in cerebral perfusion and blood volume increase, while inhibitory activity contributes to both vasodilation and vasoconstriction. How specific subpopulations of interneurons regulate the brain’s blood supply is less examined. Parvalbumin interneurons are the largest subpopulation of GABAergic neurons in the brain, critical for brain development, plasticity, and long-distance excitatory neurotransmission. Despite their essential role in brain function, the contribution of parvalbumin neurons to neurovascular coupling has been relatively unexamined. Using optical intrinsic signal imaging and laser speckle contrast imaging, we photostimulated awake and anesthetized transgenic mice expressing channelrhodopsin under a parvalbumin promoter. Increased parvalbumin activity reduced local oxygenation, cerebral blood volume, and cerebral blood flow. These “negative” hemodynamic responses were consistent within and across mice and reproducible across a broad range of photostimulus parameters. However, the sign and magnitude of the hemodynamic response resulting from increased parvalbumin activity depended on the type and level of anesthesia used. Opposed hemodynamic responses following increased excitation or parvalbumin-based inhibition suggest unique contributions from different cell populations to neurovascular coupling.     

Altered coupling of cerebral blood flow and functional connectivity strength in visual and higher order cognitive cortices in primary open angle glaucoma

Primary open-angle glaucoma (POAG) has been suggested to be a neurodegenerative disease associated with altered cerebral vascular hemodynamics and widespread disruption of neuronal activity within the visual, working memory, attention and executive networks. We hypothesized that disturbed neurovascular coupling in visual and higher order cognitive cortices exists in POAG patients and correlates with glaucoma stage and visual field defects. Through multimodal magnetic resonance imaging, we evaluated the cerebral blood flow (CBF)-functional connectivity strength (FCS) correlations of the whole gray matter and CBF/FCS ratio per voxel for all subjects. Compared with normal controls, POAG patients showed reduced global CBF-FCS coupling and altered CBF/FCS ratios, predominantly in regions in the visual cortex, salience network, default mode network, and dorsal attentional network. The CBF/FCS ratio was negatively correlated with glaucoma stage, and positively correlated with visual field defects in the lingual gyrus in POAG patients. Moreover, early brain changes were detected in early POAG. These findings indicate neurovascular coupling dysfunction might exist in the visual and higher order cognitive cortices in POAG patients and its clinical relevance. The results may contribute to the monitoring of POAG progression and provide insight into the pathophysiology of the neurodegenerative process in POAG.