Diffusion and electrogenic components of the resting potential in explanted neonatal rat ventricle cells

1987 ◽  
Vol 65 (10) ◽  
pp. 2110-2116
Author(s):  
Martine LeFloch ◽  
Otto F. Schanne ◽  
Elena Ruiz-Ceretti
Keyword(s):  
Cardiac Cells ◽  
Neonatal Rat ◽  
Resting Potential ◽  
Channel Blockers ◽  
Ca Channel ◽  
High K ◽  
The Mean ◽  
The Difference ◽  
Rat Ventricle ◽  
Steady Potential

Spontaneously beating explanted neonatal rat ventricle cells stop beating and show a steady potential (the mean resting potential, −46.2 mV at 6.0 mM Ko) when exposed to 10 mM Cao or 4 mM Mn. When Ko was increased, resting potential changed only slightly between 3 and 15 mM, but the resting potential versus Ko characteristically approached the slope of a K electrode at high Ko Elimination of Cl from the medium did not alter the K dependence of the resting potential. However, a hyperpolarization of 9 mV per 10-fold change was observed when Nao was decreased from 50 to 4 mM. Ouabain (10−4 M) depolarized the membrane within 2 min to a stable level of about −30 mV in spontaneously beating cells and in those treated with Ca channel blockers. This potential was considered as the diffusion component of the membrane potential, Vdiff. Consequently the difference between resting potential and Vdiff represents the ouabain-sensitive or the electrogenic component of the resting potential. Using linearized versions of the Mullins and Noda as well as the Goldman – Hodgkin – Katz equations, we calculated that a PNa/PK between 0.25 and 0.35, a Na/K exchange ratio of 2.0, and a Ki of 160 mM adequately described the K dependence of the resting potential. We demonstrated the contribution of electrogenic Na extrusion to the resting potential of mammalian cardiac cells in culture. Therefore the existence of a composite resting potential precludes the direct comparison of potential measurements obtained under conditions liable to independently modify either the diffusion or the electrogenic component.

Effect of calcium and cAMP on Goα expression in neonatal rat cardiac myocytes

1991 ◽  
Vol 261 (4) ◽  
pp. 15-20
Author(s):  
Karen A. Foster ◽  
Janet D. Robishaw
Keyword(s):  
Cardiac Myocytes ◽  
Inhibitory Effect ◽  
Neonatal Rat ◽  
Intracellular Camp ◽  
Dibutyryl Camp ◽  
High K ◽  
Neonatal Rat Cardiac Myocytes ◽  
Intracellular Ca ◽  
The Mean ◽  
Rat Cardiac Myocytes

Culturing neonatal rat cardiac myocytes in 50 mM KCl inhibits the accumulation of Go that occurs when myocytes are placed in culture. The mechanism by which high extracellular K+ inhibits Go accumulation in myocytes was investigated by measurement of the concentration of intracellular Ca2+ ([Ca2+]) and adenosine 3',5'-cyclic monophosphate concentration ([cAMP]) of control and K+-depolarized myocytes. Although intracellular [Ca2++] in K+-depolarized myocytes was twofold higher than basal intracellular [Ca2+] in control cells, the mean intracellular [Ca2+] in contracting control myocytes was comparable to that of K+-depolarized myocytes. Furthermore, myocytes cultured in low Ca2+ plus high K+ exhibited an inhibition of Go accumulation, even though intracellular [Ca2+] was 10-fold lower than that of cells cultured in normal Ca2+ plus high K+. In addition, intracellular [cAMP] of K+-depolarized myocytes was comparable to that of control cells. Moreover, dibutyryl cAMP inhibited Go accumulation in myocytes to the same extent as high K+, even though intracellular [cAMP] differed 10-fold. Thus neither intracellular Ca2+ nor cAMP appear to mediate the inhibitory effect of high K+ on Go accumulation. However, cAMP has an inhibitory effect on Goα expression that is independent of K+. dibutyryl cAMP; fura-2; immunoblotting

Mechanoelectrical excitation by fluid jets in monolayers of cultured cardiac myocytes

2005 ◽  
Vol 98 (6) ◽  
pp. 2328-2336 ◽  
Author(s):  
Chae-Ryon Kong ◽  
Nenad Bursac ◽  
Leslie Tung
Keyword(s):  
Cell Monolayer ◽  
Cardiac Cells ◽  
Neonatal Rat ◽  
Shear Stresses ◽  
Ca Channel ◽  
Mechanical Stimuli ◽  
Ventricular Cells ◽  
Fluid Jets ◽  
Reentrant Arrhythmia ◽  
Longitudinal Stretch

Although the prevailing view of mechanoelectric feedback (MEF) in the heart is in terms of longitudinal cell stretch, other mechanical forces are considerable during the cardiac cycle, including intramyocardial pressure and shear stress. Their contribution to MEF is largely unknown. In this study, mechanical stimuli in the form of localized fluid jet pulses were applied to neonatal rat ventricular cells cultured as confluent monolayers. Such pulses result in pressure and shear stresses (but not longitudinal stretch) in the monolayer at the point of impingement. The goal was to determine whether these mechanical stimuli can trigger excitation, initiate a propagated wave, and induce reentry. Cells were stained with the voltage-sensitive dye RH237, and multi-site optical mapping was used to record the spread of electrical activity in isotropic and anisotropic monolayers. Pulses (10 ms) with velocities ranging from 0.3 to 1.8 m/s were applied from a 0.4-mm diameter nozzle located 1 mm above the cell monolayer. Fluid jet pulses resulted in circular wavefronts that propagated radially from the stimulus site. The likelihood for mechanical stimulation was quantified as an average stimulus success rate (ASSR). ASSR increased with jet amplitude and time waited between stimuli and decreased with the application of gadolinium and streptomycin, blockers of stretch-activated channels, but not with nifedipine, a blocker of the L-type Ca channel. Absence of cellular injury was confirmed by smooth propagation maps and propidium iodide stains. In rare instances, the mechanical pulse resulted in the induction of reentrant activity. We conclude that mechanical stimuli other than stretch can evoke action potentials, propagated activity, and reentrant arrhythmia in two-dimensional sheets of cardiac cells.

Direct observation of radial intracellular P O 2 gradients in a single cardiomyocyte of the rat

1998 ◽  
Vol 275 (1) ◽  
pp. H225-H233 ◽  
Author(s):  
Eiji Takahashi ◽  
Keiko Sato ◽  
Hiroshi Endoh ◽  
Zhe-Long Xu ◽  
Katsuhiko Doi
Keyword(s):  
Oxygen Consumption ◽  
Cardiac Cells ◽  
Facilitated Diffusion ◽  
Single Individual ◽  
Radial Profiles ◽  
Carbonyl Cyanide ◽  
Increase Oxygen Consumption ◽  
The Mean ◽  
Rat Ventricle

The purpose of the present study was to directly visualize radial gradients of intracellular [Formula: see text] in a single individual cardiomyocyte isolated from the rat ventricle. Microspectrophotometry with the use of cytosolic myoglobin as an oxygen probe was conducted at 410 nm. When the quiescent cell was incubated with 1 μM carbonyl cyanide m-chlorophenylhydrazone to increase oxygen consumption approximately eightfold, gradual decreases in myoglobin oxygen saturation (SMb) were demonstrated toward the core of the cell, whereas these decreases disappeared when the cell was treated with 2 mM NaCN. These results highlighted the importance of diffusional oxygen transport in determining intracellular oxygenation in cardiac cells. From the measured SMb, we assessed the profile of radial changes in intracellular [Formula: see text]at the mean SMb comparable to that in vivo (∼0.5). Quite steep [Formula: see text]gradients were demonstrated in the vicinity of the sarcolemma that were rapidly attenuated toward the cell core. These radial profiles of intracellular [Formula: see text] demonstrate the significance of myoglobin-facilitated diffusion of oxygen. Furthermore, the shallow gradients of [Formula: see text] near the center of the cell might arise from partial depression of oxygen consumption near the cell core.

Effects of K-channel blockers, calcium, and verapamil suggest different pacemaker mechanisms in cultured neonatal rat and embryonic chick ventricle cells

1989 ◽  
Vol 67 (7) ◽  
pp. 795-800 ◽  
Author(s):  
Otto F. Schanne ◽  
L. Boutin ◽  
J. Derosiers
Keyword(s):  
Cardiac Cells ◽  
Neonatal Rat ◽  
K Channel ◽  
Chronotropic Effect ◽  
Inward Current ◽  
Diastolic Depolarization ◽  
K Current ◽  
Beating Rate ◽  
Rat Ventricle ◽  
Diastolic Potential

We compared the determinants of spontaneous activity in explanted neonatal (2-day-old) rat ventricle cells and in reaggregates derived from 15-day-old chick embryos. We studied the beating rate with an optical recording method and the underlying electrical activity with glass microelectrodes using the K current blockers cesium (Cs) and tetraethylammonium, varied Ca concentrations, and the Ca antagonist verapamil. In the rat (i) Cs increased the beating rate that was mediated by an increase in the slope of the diastolic potential, (ii) Ca increased the beating rate dramatically at low and medium concentrations to decrease it again at 8 mM Cao.2This increase in the beating rate was mediated by an increase of the slope of the diastolic depolarization. (iii) The beating rate decreased with verapamil at concentrations between 0.5 and 2.0 μM. The effects of Cs and Ca suggest that an increase in net inward current (block of IK1) underlies the positive chronotropic effect of Cs and that the pacemaker mechanism is determined by a Ca inward current or an IT1 type current modulated by variations of Cai. In the chick reaggregates (i) Cs and tetraethylammonium decreased the beating rate that was mainly brought about by a decrease in the slope of diastolic depolarization. (ii) Ca increased the beating rate but to a lesser degree than in the rat and there was no decrease of the beating rate at higher concentrations. (iii) The increase in the beating rate was not mediated by an increase in the slope of the diastolic potential but mainly by a depolarization of the maximum diastolic potential. (iv) Verapamil inhibited electrogenesis before any change in the diastolic potential was evident. The negative chronotropic effect of Cs and tetraethylammonium is compatible with the notion that a voltage- and time-dependent K current was inhibited and that this current determines the pacemaker. Moreover, the Ca component of the pacemaker mechanism in explanted rat ventricle cells resembles either that of the sinoatrial node or represents triggered activity.Key words: pacemaker mechanism, cultured cardiac cells, K-channel blocker, calcium, verapamil.

scholarly journals Photoinduced removal of nifedipine reveals mechanisms of calcium antagonist action on single heart cells.

1985 ◽  
Vol 86 (3) ◽  
pp. 353-379 ◽  
Author(s):  
A M Gurney ◽  
J M Nerbonne ◽  
H A Lester
Keyword(s):  
Calcium Channels ◽  
Dissociation Constants ◽  
Light Flash ◽  
Cardiac Cells ◽  
Current Amplitude ◽  
Neonatal Rat ◽  
Resting Potential ◽  
Open Channels ◽  
Heart Cell ◽  
Heart Cells

The currents through voltage-activated calcium channels in heart cell membranes are suppressed by dihydropyridine calcium antagonists such as nifedipine. Nifedipine is photolabile, and the reduction of current amplitude by this drug can be reversed within a few milliseconds after a 1-ms light flash. The blockade by nifedipine and its removal by flashes were studied in isolated myocytes from neonatal rat heart using the whole-cell clamp method. The results suggest that nifedipine interacts with closed, open, and inactivated calcium channels. It is likely that at the normal resting potential of cardiac cells, the suppression of current amplitude arises because nifedipine binds to and stabilizes channels in the resting, closed state. Inhibition is enhanced at depolarized membrane potentials, where interaction with inactivated channels may also become important. Additional block of open channels is suggested when currents are carried by Ba2+ but is not indicated with Ca2+ currents. Numerical simulations reproduce the experimental observations with molecular dissociation constants on the order of 10(-7) M for closed and open channels and 10(-8) M for inactivated channels.

Modulation of Ca by agents affecting voltage-sensitive Ca channels in mesangial cells

1989 ◽  
Vol 257 (6) ◽  
pp. F1094-F1099 ◽  
Author(s):  
Y. M. Yu ◽  
F. Lermioglu ◽  
A. Hassid
Keyword(s):  
Mesangial Cells ◽  
Mechanisms Of Action ◽  
Bay K 8644 ◽  
Channel Blockers ◽  
Ca Channel ◽  
Ca Channels ◽  
High K ◽  
Ca Channel Blockers ◽  
Lanthanum Ion ◽  
Channel Activator

The purpose of this study was to investigate the effects of depolarizing media and of Ca-channel activators and blockers on cytosolic free Ca in cultured rat mesangial cells. Membrane depolarizing media, containing 10–100 mM K+, dose dependently increased cytosolic Ca, and this effect was sustained and reversible. Nifedipine and lanthanum ion inhibited this increase, whereas verapamil was ineffective. A Ca-channel activator, BAY K 8644, dose dependently increased resting Ca levels, and nifedipine inhibited this effect. Moreover, the increase of Ca induced by maximally effective high K+ and BAY K 8644 was additive, suggesting differential mechanisms of action for the two channel activators. Nifedipine and verapamil decreased resting Ca levels by up to 35–40%. The results support the idea that mesangial cells have spontaneously active Ca channels that can be further activated by membrane depolarization or by the Ca-channel activator, BAY K 8644, and inhibited by the Ca-channel blockers, nifedipine or verapamil. Voltage-sensitive Ca channels in mesangial cells may play a role in the regulation of the glomerular filtration rate.

Modulation of ureteric Ca signaling and contractility in humans and rats by uropathogenic E. coli

2010 ◽  
Vol 298 (4) ◽  
pp. F900-F908 ◽  
Author(s):  
Rachel V. Floyd ◽  
Craig Winstanley ◽  
Ali Bakran ◽  
Susan Wray ◽  
Theodor V. Burdyga
Keyword(s):  
K Channel ◽  
Channel Blockers ◽  
Ca Channel ◽  
Dependent Manner ◽  
E Coli ◽  
High K ◽  
Significant Impairment ◽  
Ca Signaling ◽  
Tract Infections ◽  
Increased Activity

Ascending urinary tract infections, a significant cause of kidney damage, are predominantly caused by uropathogenic Escherichia coli (UPEC). However, the role and mechanism of changes in ureteric function during infection are poorly understood. We therefore investigated the effects of UPEC on Ca signaling and contractions in rat ( n = 17) and human ( n = 6) ureters. Ca transients and force were measured and effects of UPEC on the urothelium were monitored in live tissues. In both species, luminal exposure of ureters to UPEC strains J96 and 536 caused significant time-dependent decreases in phasic and high K depolarization-induced contractility, associated with decreases in the amplitude and duration of the Ca transients. These changes were significant after 3–5 h and irreversible over the next 5 h. The infection causes increased activity of K channels, causing inhibition of voltage-gated Ca entry, and K channel blockers could reverse the effects of UPEC on ureteric function. A smaller direct effect on Ca entry also occurs. Nonpathogenic E. coli (TG2) or abluminal application of UPEC did not produce changes in Ca signaling or contractility. UPEC exposure also caused significant impairment of urothelial barrier function; luminal application of the Ca channel blocker nifedipine caused a reduction in contractions as it entered the tissue, an effect not observed in untreated ureters. Thus, UPEC impairs ureteric contractility in a Ca-dependent manner, largely caused by stimulation of potassium channels and this mechanism is dependent on host-urothelium interaction.

scholarly journals Myofilament-generated tension oscillations during partial calcium activation and activation dependence of the sarcomere length-tension relation of skinned cardiac cells.

1978 ◽  
Vol 72 (5) ◽  
pp. 667-699 ◽  
Author(s):  
A Fabiato ◽  
F Fabiato
Keyword(s):  
Sarcomere Length ◽  
Rapid Decrease ◽  
Cardiac Cells ◽  
Maximal Velocity ◽  
Active Tension ◽  
Velocity Of Shortening ◽  
Rigor Tension ◽  
The Mean ◽  
Rat Ventricle ◽  
Full Activation

During partial Ca2+ activation, skinned cardiac cells with sarcoplasmic reticulum destroyed by detergent developed spontaneous tension oscillations consisting of cycles (0.1-1 Hz) of rapid decrease of tension corresponding to the yield of some sarcomeres and slow redevelopment of tension corresponding to the reshortening of these sarcomeres. Such myofilament-generated tension oscillations were never observed during the full activation induced by a saturating [free Ca2+] or during the rigor tension induced by decreasing [MgATP] in the absence of free Ca2+ or when the mean sarcomere length (SL) of the preparation was greater than 3.10 microm during partial Ca2+ activation. A stiff parallel elastic element borne by a structure that could be digested by elastase hindered the study of the SL--active tension diagram in 8-13-microm-wide skinned cells from the rat ventricle, but this study was possible in 2-7-microm-wide myofibril bundles from the frog or dog ventricle. During rigor the tension decreased linearly when SL was increased from 2.35 to 3.80 microm. During full Ca2+ activation the tension decreased by less than 20% when SL was increased from 2.35 to approximately 3.10 microm. During partial Ca2+ activation the tension increased when SL was increased from 2.35 to 3.00 microm. From this observation of an apparent increase in the sensitivity of the myofilaments to Ca2+ induced by increasing SL during partial Ca2+ activation, a model was proposed that describes the tension oscillations and permits the derivation of the maximal velocity of shortening (Vmax). Vmax was increased by increasing [free Ca2+] or decreasing [free Mg2+] but not by increasing SL.

The Effect of Vocabulary Intervention on Text Comprehension: Who Benefits?

2019 ◽  
Vol 50 (4) ◽  
pp. 562-578 ◽  
Author(s):  
Dawna Duff
Keyword(s):  
Middle School ◽  
Reading Comprehension ◽  
Text Comprehension ◽  
Classroom Instruction ◽  
Vocabulary Instruction ◽  
Clinical Intervention ◽  
Vocabulary Knowledge ◽  
Vocabulary Intervention ◽  
The Mean ◽  
The Difference

Purpose Vocabulary intervention can improve comprehension of texts containing taught words, but it is unclear if all middle school readers get this benefit. This study tests 2 hypotheses about variables that predict response to vocabulary treatment on text comprehension: gains in vocabulary knowledge due to treatment and pretreatment reading comprehension scores. Method Students in Grade 6 ( N = 23) completed a 5-session intervention based on robust vocabulary instruction (RVI). Knowledge of the semantics of taught words was measured pre- and posttreatment. Participants then read 2 matched texts, 1 containing taught words (treated) and 1 not (untreated). Treated texts and taught word lists were counterbalanced across participants. The difference between text comprehension scores in treated and untreated conditions was taken as a measure of the effect of RVI on text comprehension. Results RVI resulted in significant gains in knowledge of taught words ( d RM = 2.26) and text comprehension ( d RM = 0.31). The extent of gains in vocabulary knowledge after vocabulary treatment did not predict the effect of RVI on comprehension of texts. However, untreated reading comprehension scores moderated the effect of the vocabulary treatment on text comprehension: Lower reading comprehension was associated with greater gains in text comprehension. Readers with comprehension scores below the mean experienced large gains in comprehension, but those with average/above average reading comprehension scores did not. Conclusion Vocabulary instruction had a larger effect on text comprehension for readers in Grade 6 who had lower untreated reading comprehension scores. In contrast, the amount that children learned about taught vocabulary did not predict the effect of vocabulary instruction on text comprehension. This has implications for the identification of 6th-grade students who would benefit from classroom instruction or clinical intervention targeting vocabulary knowledge.

Efficacy and Safety of Oral Ivermectin and Topical Permethrin in the Treatment of Scabies

2020 ◽  
Vol 33 (1) ◽  
pp. 41-47
Author(s):  
Mohsena Akhter ◽  
Ishrat Bhuiyan ◽  
Zulfiqer Hossain Khan ◽  
Mahfuza Akhter ◽  
Gulam Kazem Ali Ahmad ◽  
...  
Keyword(s):  
Skin Diseases ◽  
Close Contact ◽  
Randomized Study ◽  
Sarcoptes Scabiei ◽  
Efficacy And Safety ◽  
Common Skin ◽  
Group A ◽  
The Mean ◽  
The Difference ◽  
Group B

Background: Scabies is one of the most common skin diseases in our country. It is caused by the mite Sarcoptes scabiei var hominis, which is an ecto-parasite infesting the epidermis. Scabies is highly contagious. Prevalence is high in congested or densely populated areas. Individuals with close contact with an affected person should be treated with scabicidal which is available in both oral and topical formulations. The only oral but highly effective scabicidal known to date is Ivermectin. Amongst topical preparations, Permethrin 5 % cream is the treatment of choice. Objective: To evaluate the efficacy & safety of oral Ivermectin compared to topical Permethrin in the treatment of scabies. Methodology: This prospective, non-randomized study was conducted at the out-patient department of Dermatology and Venereology of Shaheed Suhrawardy Medical College & Hospital over a period of 6 months, from August 2016 to January 2017. The study population consisted of one hundred patients having scabies, enrolled according to inclusion criteria. They were divided into two groups. group A was subjected to oral Ivermectin and the group B to Permethrin 5% cream. Patients were followed up on day 7 and 14 for assessment of efficacy and safety. Result: The mean scoring with SD in group A (Ivermectin) and group B (Permethrin) were 8.26 ± 2.22 and 7.59 ± 2.01 respectively at the time of observation. The difference between the mean score of the two group is not significant (p=0.117) the mean scoring with SD in group A and group B were 4.54 ± 2.05 and 1.64 ± 1.84 respectively at 7thdays. The difference between the mean score of the two group is significant (p<0.001). The mean scoring with SD in group A and group B were 2.68± 2.35 and .36± 1.10 respectively at 14th day difference between the mean score of the group is significant (p<0.001). Conclusion: Topical application of permethrin 5% cream is more effective and safer than oral Ivermectin in the treatment of scabies. TAJ 2020; 33(1): 41-47

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