Mathematical Simulation of Slowing of Cardiac Conduction Velocity by Elevated Extracellular [K+] in a Human Atrial Strand

We have studied the dependence of conduction velocity () on extracellular potassium concentration ([K⁺]_o) in a model of one-dimensional conduction using an idealized strand of human atrial cells. Elevated [K⁺]_o in the 5–20 mM range shifts the resting potential (V _rest) in the depolarizing direction and reduces input resistance (R _in) by increasing an inwardly rectifying K⁺ conductance, I _Kl.Our results show that in this model: (1) depends on [K⁺] in a biphasic fashion. Moderate elevations of [K⁺]_o (to less than 8 mM) result in a small increase in , whereas at higher [K⁺]_o (8–16 mM) is reduced. (2) This biphasic relationship can be attributed to the competing effects of (i) the smaller depolarization needed to reach the excitation threshold (V _thresh-V _rest) and (ii) reduced availability (increased inactivation) of sodium current, I _Na, as the cell depolarizes progressively. (3) Decreasing R _in reduces due to the increased electrical load on surrounding cells. (4) The effect on of [K⁺]_o-induced changes in R _inin the atrium (as well as other high-R _in tissue, such as that of the Purkinje system or nodes) is likely to be small. This effect could be substantial, however, under conditions in which R _in is comparable in size to gap junction resistance and membrane resistance (inverse slope of the whole-cell current–voltage relationship) when sodium channels are open, which is likely to be the case in ventricular tissue. © 2000 Biomedical Engineering Society.PAC00: 8716Uv, 8719Hh, 8716Ac     

Model study of the spread of electrotonic potential in cardiac tissue

This model study describes the electrotonic response of a cable model of cardiac tissue stimulated at one point. The stimulus is applied intracellularly in the form of a 2ms pulse of current of near threshold amplitude. The attenuation of the electrotonic potential with distance and its mode of propagation along the cable are compared for equivalent passive, continuous and discontinuous cables. The three structures have the same basic physical and electrical characteristic and they differ either with respect to being active or passive or to the presence or absence of intercellular gap junctions. In the continuous cable a just subthreshold stimulus produces a local active response which propagates more slowly and is attenuated less rapidly with distance than in a passive cable. The spatial decrement of the local response in a discontinuous cable is faster than in a continuous cable of equal average resistivity. It is suggested that the larger time constant of the foot of the action potential observed in the longitudinal direction in cardiac muscle could be due in part to the electrotonic spread of the local response from the site of stimulation.     

Electrical resistance of cell membranes in Necturus kidney

Summary The two-dimensional cable analysis for flat epithelia was made suitable for the study of current and voltage distribution in cylindrical epithelia which are assumed to have low paracellular shunt resistance. Applying the solutions to the proximal tubule of the doubly perfused volume-expanded Necturus kidney, the sum of cell membrane conductances in parallel, (g+g), was determined and found to be 0.56 mmho/cm². From this figure, the theoretical upper limit for the sum of membrane conductances in series may be estimated at 0.14 mmho/cm², though a figure of 0.105 mmho/cm² appears more realistic for this limit (membrane resistance in series equal to or greater than 9500 ohm·cm²). The core resistanvity, , of the proximal cell column was 11100 ohm·cm. When the kidney was perfused with sodium benzene sulfonate, choline chloride or LiCl, the figures for (g+g) and were 0.48 mmho/cm² and 15360 ohm·cm, 0.67 mmho/cm² and 55600 ohm·cm and 0.40 mmho/cm² and 4630 ohm·cm respectively.     

Effects of dinitrophenol on active-transport processes and cell membranes in the Malpighian tubule of Formica

In Formica Malpighian tubules KCl secretion is driven by a V-type H⁺ ATPase in the luminal membrane in parallel with a H⁺/K⁺ antiporter. The effect of the protonophore dinitrophenol (DNP) was investigated on the isolated, symmetrically perfused tubule. DNP was applied in two different concentrations: 0.2 mmol/l and 1 mmol/l. The effects were fast and rapidly reversible. The equivalent short-circuit current (I _sc) was reduced significantly to respectively 25±3% Cn=4) and –3±7% (n=11) of the control value when 0.2 mmol/ l or 1 mmol/l was added to the bath. When 1 mmol/l DNP was applied the transepithelial resistance (R _te) decreased significantly to 74±11% of the control value (n=11), and the luminal over basolateral voltage divider ratio (VDR), providing an estimate of luminal over basolateral membrane resistance, decreased to 37±12% of the control (n=6). A concentration of 1 mmol/l DNP was also applied from the lumen. The decrease in I _sc was significant, but much less pronounced (74±5% of control; n=6) and no significant changes in R _te and VDR were observed. It is argued that, when the concentration in the bath is high enough, DNP may cross the cell and have a protonophoric effect not only on the mitochondria but also across the luminal cell membrane explaining the drop in transepithelial and in relative luminal membrane resistance. The diminished effectiveness of DNP, when applied from the luminal side, suggests that the luminal membrane is somehow less permeable to toxic substances, but that DNP very rapidly enters the cell via the basolateral membrane and may bring about an initial protonophoric effect across this membrane.     

tDCS possibly stimulates glial cells

Objective

Explore the possibility that transcranial direct current stimulation (tDCS) of the brain affects glial cells.

Methods

Cable theory is used to estimate roughly transmembrane potential in neurons and glial cells. tDCS is additionally compared to neuronal stimulation techniques for which the mechanisms are well known.

Results

Theoretical calculations indicated that tDCS can affect the glial transmembrane potential. The change is similar to what is physiologically observed in astrocytes during neuronal activation. In neurons, transmembrane potential changes are much weaker than the threshold for eliciting action potentials.

Conclusions

Based on simplified cable theory, tDCS may affect glial cells’ transmembrane potential and thereby the balance of neurotransmitters. No physiological evidence or proof is available, however.

Significance

It is an exciting possibility that tDCS could manipulate glial cells because they are active participants in brain function, and have multiple essential roles in the human brain. This approach may change greatly the therapeutic potential of tDCS, and also affects the safety considerations.     

An inter-laboratory comparison study on transfer,persistence and recovery of DNA from cable ties

To address questions on the activity that led to the deposition of biological traces in a particular case, general information on the probabilities of transfer, persistence and recovery of cellular material in relevant scenarios is necessary. These figures may be derived from experimental data described in forensic literature when conditions relevant to the case were included. The experimental methodology regarding sampling, DNA extraction, DNA typing and profile interpretation that were used to generate these published data may differ from those applied in the case and thus the applicability of the literature data may be questioned. To assess the level of variability that different laboratories obtain when similar exhibits are analysed, we performed an inter-laboratory study between four partner laboratories. Five sets of 20 cable ties bound by different volunteers were distributed to the participating laboratories and sampled and processed according to the in-house protocols. Differences were found for the amount of retrieved DNA, as well as for the reportability and composition of the DNA profiles. These differences also resulted in different probabilities of transfer, persistence and recovery for each laboratory. Nevertheless, when applied to a case example, these differences resulted in similar assignments of weight of evidence given activity-level propositions.     

微创Cable-Pin系统和改良张力带内固定治疗髌骨横形骨折的疗效比较

目的比较微创Cable-Pin系统和改良张力带内固定治疗闭合性髌骨横形骨折的疗效。方法采用微创CablePin系统内固定治疗髌骨横形骨折30例(微创组),采用切开复位改良张力带内固定治疗髌骨横形骨折30例(张力带组)。比较2组手术时间、骨折愈合时间、术后VAS评分、膝关节屈曲度、膝关节功能Bostman评分、并发症。结果微创组手术时间(54.3±9.8)min,较张力带组(48.5±6.1)min长,但差异无统计学意义(t=1.990,P=0.100)。微创组骨折愈合时间(6.8±2.7)周,较张力带组(11.5±1.2)周明显缩短,差异有统计学意义(t=9.350,P=0.001)。微创组术后前3个月的VAS评分明显高于张力带组,差异有统计学意义(P0.05);术后6个月2组差异无统计学意义(P0.05)。微创组术后1、2、3、6、12、18个月膝关节功能屈曲度都大于张力带组,差异有统计学意义(P0.05)。术后3、6、12、18个月微创组膝关节功能Bostman评分明显优于张力带组,差异有统计学意义(P0.05)。结论微创Cable-Pin系统治疗髌骨骨折在术后疼痛、骨折愈合时间、膝关节屈曲度、膝关节功能评分和并发症方面要优于切开复位改良张力带内固定。     

两种线缆不同内固定方法治疗髌骨骨折疗效比较

目的探讨采用带尾孔针缆及线缆固定两种不同方法治疗髌骨骨折的临床疗效。方法选取40例髌骨骨折,其中18例行带尾孔针缆系统治疗(针缆组),22例行线缆环扎固定治疗(线缆组)。参照Bostman标准评价两组的临床疗效。结果针缆组手术时间为40.15~56.52 min,与线缆组的42.22~53.21 min比较差异无统计学意义(P>0.05);针缆组骨折愈合时间(10±2)周短于线缆组(14±2)周,差异有统计学意义(P<0.05);针缆组获随访(12.00±4.34)个月,Bostman评分优良率100.0%;线缆组随访(16.46±2.82)个月,Bostman评分优良率90.9%,两组优良率比较差异有统计学意义(P<0.05),两组术后无一例发生感染。结论采用带尾孔针缆系统治疗髌骨骨折具有固定牢固、并发症少、术后骨折愈合时间短、患膝功能恢复好等优点,值得推广应用。     

长Gamma钉结合有限切开复位钛缆环扎固定治疗ScinsheimerⅢ～Ⅴ型股骨粗隆下骨折

目的探讨长Gamma钉结合有限切开复位钛缆环扎固定治疗ScinsheimerⅢ～Ⅴ型股骨粗隆下骨折的临床疗效和手术技巧。方法 2012年7月至2017年6月治疗ScinsheimerⅢ～Ⅴ型股骨粗隆下骨折共31例,其中,男24例,女7例,平均年龄(46.4±8.7)岁。术前按Scinsheimer分类:ⅢA型11例,ⅢB型9例,Ⅳ型6例,Ⅴ型5例。手术先用牵引床初步复位,然后有限切开,综合采用多种微创方法复位骨折块,钛缆环扎固定骨折块,再自大粗隆顶点顺行插入长Gamma钉进行固定。临床疗效评定采用Harris髋关节功能评分标准及影像学评价。结果患者均获得随访,时间12～24个月。骨折均愈合,骨折愈合时间平均17.6(12～34)周,无感染、内固定物松动断裂、骨不连、肢体短缩、髋内翻、畸形愈合等并发症。末次随访髋关节功能Harris评分结果:优24例,良5例,可2例,优良率为93.5%。结论长Gamma钉结合有限切开复位钛缆环扎固定治疗ScinsheimerⅢ～Ⅴ型股骨粗隆下骨折具有创伤小、内固定牢靠及术后并发症少等优点,值得临床推广。     

股骨假体周围骨折治疗的对策

目的探讨髋关节置换术后股骨假体周围骨折的治疗对策。方法对2000～2006年11例临床病例应用钢板钢缆系统行内固定植骨融合术，对结果进行评价。结果11例假体均稳定，骨折愈合，行走步态良好。结论钢板钢缆系统是治疗髋关节置换术后股骨假体周围骨折的有效方法。