scholarly journals The effect of temperature on spontaneous action potential discharge of the isolated sinus venosus from winter and summer plaice (Pleuronectes platessa)

1995 ◽  
Vol 198 (1) ◽  
pp. 137-140 ◽  
Author(s):  
A A Harper ◽  
I P Newton ◽  
P W Watt
Keyword(s):  
Action Potential ◽  
Discharge Rate ◽  
Cardiac Pacemaker ◽  
Intrinsic Rate ◽  
Effect Of Temperature ◽  
Pacemaker Activity ◽  
Duration Of Action ◽  
Diastolic Depolarization ◽  
Significant Difference

The spontaneous cardiac pacemaker activity and conformation were recorded in vitro, using intracellular recording methods, from heart tissue of summer- and winter-caught plaice. The effects of changing temperature on the pacemaker rate, duration of action potential and diastolic depolarization were investigated by altering the temperature of the superfusing medium. The resting intrinsic rate of discharge was significantly greater in pacemaker cells from winter plaice (P=0.05), but there was no significant difference between winter and summer fish in the apparent Arrhenius activation energies for this process. However, there was a significant difference in the estimated intercept, indicating a thermal shift in the processes underlying the spontaneous pacemaker rhythm. There was no significant difference in the diastolic depolarization duration recorded from winter and summer fish over the temperature range 4­22 °C. The major effect of previous environmental temperature was on the duration of the action potential (P<0.02), indicating that the observed changes in pacemaker discharge rate were not influenced by the processes that determine the duration of the pacemaker diastolic depolarisation but were modulated by the channel events that give rise to the action potential.

Contribution of Nav1.8 Sodium Channels to Action Potential Electrogenesis in DRG Neurons

2001 ◽  
Vol 86 (2) ◽  
pp. 629-640 ◽  
Author(s):  
Muthukrishnan Renganathan ◽  
Theodore R. Cummins ◽  
Stephen G. Waxman
Keyword(s):  
Action Potential ◽  
Sodium Channels ◽  
Action Potentials ◽  
Input Resistance ◽  
Resting Membrane Potential ◽  
Drg Neurons ◽  
Significant Difference ◽  
Steady State Inactivation ◽  
Current Threshold

C-type dorsal root ganglion (DRG) neurons can generate tetrodotoxin-resistant (TTX-R) sodium-dependent action potentials. However, multiple sodium channels are expressed in these neurons, and the molecular identity of the TTX-R sodium channels that contribute to action potential production in these neurons has not been established. In this study, we used current-clamp recordings to compare action potential electrogenesis in Nav1.8 (+/+) and (−/−) small DRG neurons maintained for 2–8 h in vitro to examine the role of sodium channel Nav1.8 (α-SNS) in action potential electrogenesis. Although there was no significant difference in resting membrane potential, input resistance, current threshold, or voltage threshold in Nav1.8 (+/+) and (−/−) DRG neurons, there were significant differences in action potential electrogenesis. Most Nav1.8 (+/+) neurons generate all-or-none action potentials, whereas most of Nav1.8 (−/−) neurons produce smaller graded responses. The peak of the response was significantly reduced in Nav1.8 (−/−) neurons [31.5 ± 2.2 (SE) mV] compared with Nav1.8 (+/+) neurons (55.0 ± 4.3 mV). The maximum rise slope was 84.7 ± 11.2 mV/ms in Nav1.8 (+/+) neurons, significantly faster than in Nav1.8 (−/−) neurons where it was 47.2 ± 1.3 mV/ms. Calculations based on the action potential overshoot in Nav1.8 (+/+) and (−/−) neurons, following blockade of Ca2+ currents, indicate that Nav1.8 contributes a substantial fraction (80–90%) of the inward membrane current that flows during the rising phase of the action potential. We found that fast TTX-sensitive Na+ channels can produce all-or-none action potentials in some Nav1.8 (−/−) neurons but, presumably as a result of steady-state inactivation of these channels, electrogenesis in Nav1.8 (−/−) neurons is more sensitive to membrane depolarization than in Nav1.8 (+/+) neurons, and, in the absence of Nav1.8, is attenuated with even modest depolarization. These observations indicate that Nav1.8 contributes substantially to action potential electrogenesis in C-type DRG neurons.

scholarly journals Temperature, Leaf Wetness, and Isolate Effects on Infection of Minneola Tangelo Leaves by Alternaria sp.

Plant Disease ◽  
1999 ◽  
Vol 83 (5) ◽  
pp. 429-433 ◽  
Author(s):  
Y. Canihos ◽  
T. L. Peever ◽  
L. W. Timmer
Keyword(s):  
Polynomial Equation ◽  
Brown Spot ◽  
Effect Of Temperature ◽  
Leaf Wetness ◽  
Significant Difference ◽  
Alternaria Brown Spot ◽  
Detached Leaves ◽  
Alternaria Sp ◽  
Response To Temperature

Alternaria brown spot causes necrotic lesions on immature leaves, twigs, and fruit of tangerines and their hybrids, reducing yield and fruit quality. The effect of temperature, leaf wetness, and isolate was evaluated in an in vitro system using immature detached leaves of Minneola tangelo Infection was greatest at 27°C, decreased gradually as the temperature declined to 24, 20, and 17°C, and dropped sharply at 32°C. Levels of infection were low at 4 and 8 h of leaf wetness and continued to increase with longer wetting periods up to 36 h. A polynomial equation was developed that provided a good fit for the data (adjusted R2 = 0.93). Isolates differed in aggressiveness, but there was no significant difference among isolates in their response to temperature and leaf wetness duration.

PDE4B and PDE4D differentially regulate cardiac pacemaker activity

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
WPV Pereira De Vasconcelos ◽  
AMG Gomez ◽  
RF Fischmeister ◽  
GV Vandecasteele ◽  
DM Mika
Keyword(s):  
Ventricular Myocytes ◽  
Cardiac Pacemaker ◽  
Hydrolytic Activity ◽  
Pde4 Inhibitor ◽  
Pacemaker Activity ◽  
National Budget ◽  
Beating Rate ◽  
Public Grant

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Agence Nationale de la Recherche (ANR) Background Heart rate (HR) is generated by spontaneous electrical activity in the sinoatrial node (SAN) and is modulated by the autonomic nervous system. During sympathetic stimulation, the activation of β-adrenergic receptors (βAR) increases cAMP levels, leading to positive chronotropic effect. Among the 6 cardiac cAMP-PDE families, PDE4 is critical for controlling excitation-contraction coupling (ECC) during β-stimulation in atrial and ventricular myocytes. PDE4 may also be important for automaticity. 3 genes encode for PDE4 in the heart (pde4a, 4b, 4d). We propose to investigate their respective contribution to the regulation of pacemaker activity.  Methods Total PDE activity in mouse SAN was determined as the cAMP-hydrolytic activity measured in the absence of PDE inhibitor and the fraction corresponding to PDE4 activity was assessed by including the PDE4 inhibitor Ro-20-1724. The in vitro pacemaker activity was assessed by measuring spontaneous Ca2+ transients in Fluo4-loaded-SAN tissue from wild-type (WT) and PDE4KO mice. Images were obtained using confocal microscopy. Telemetry EKG was recorded in conscious mice in control (CTRL) conditions, after pharmacological denervation with atropine (1 mg/kg) and propranolol (2 mg/kg) and after β-stimulation with isoproterenol (ISO, 1.5 mg/kg). HR variability was evaluated by calculating the SDNN (standard deviation of RR intervals) parameter. Results Ro-20-1724 (10 µM) increased beating rate of intact SAN and increased PKA-phosphorylation of key ECC actors (ryanodine receptor, phospholamban and contractile proteins). PDE4 activity was found to account for 60% of total cAMP-PDE activity in SAN. PDE4A, 4B and 4D isoforms were found to be expressed in mouse SAN. In PDE4BKO SAN, the effect of ISO on SAN beating rate was higher than in WT. Ablation of PDE4D induced decreased beating rate in CTRL and ISO conditions and increased Ca2+ spark frequency compared to WT SAN. In vivo, PDE4BKO and PDE4DKO mice displayed increased resting HR during day and night. HR variability was decreased in PDE4BKO, but not in PDE4DKO mice during the day, and decreased in both genotypes at night compared to WT mice. After atropine + propranolol denervation, the rhythmic phenotype was only maintained in PDE4BKO but not in PDE4DKO mice. The response to β-AR stimulation with ISO was higher in PDE4BKO than in PDE4DKO. In addition, under ISO we observed an increased number of premature beats and atrioventricular blocks in PDE4DKO, but not in PDE4BKO mice. Conclusion PDE4B and PDE4D differentially regulate cardiac pacemaker activity. While PDE4B clearly controls intrinsic SAN automaticity, PDE4D might be important for ANS-mediated regulation of HR and conduction.

Effect of temperature and Zn2+ on isometric contractile properties and electrical phenomena of frog (Rana) and Xenopus skeletal muscle fibers

1984 ◽  
Vol 62 (12) ◽  
pp. 1511-1517 ◽  
Author(s):  
Toshiharu Oba ◽  
Yumiko Takagi ◽  
Ken Hotta
Keyword(s):  
Action Potential ◽  
Rana Catesbeiana ◽  
Muscle Fibers ◽  
Contractile Properties ◽  
Effect Of Temperature ◽  
Duration Of Action ◽  
Time To Peak ◽  
Effects Of Temperature ◽  
Maximum Rate Of Rise ◽  
Tubular Morphology

Effects of temperature and Zn2+ on the isometric contractile properties of toe muscle fibers of Rana catesbeiana and Xenopus laevis were studied. The maximum twitch tension almost doubled when the temperature was lowered from 20 to 4 °C in Rana muscles but not in Xenopus muscles, although the duration of action potential in Xenopus muscle was increased slightly more than that seen in the Rana species. The maximum rate of rise of tension was greater in Xenopus muscle than in the Rana muscle, at 20 °C. The prolongation of the time-to-peak tension following exposure to low temperature (4 °C) was more pronounced in Rana than in Xenopus muscles. These results suggest that the speed of release and reuptake of Ca2+ by the sarcoplasmic reticulum (SR) differs in Rana and Xenopus muscles and that these factors may be related to differences in the SR and the T-tubular morphology. In Rana muscles, Zn2+ prolonged the falling phase of the action potential and potentiated the twitch tension. In Xenopus muscles, Zn2+ marginally prolonged the duration of action potential and the twitch tension was not markedly potentiated. These results indicate that Zn2+ potentiates the twitch tension by prolonging the action potential and that Rana muscles are more sensitive to the effects of Zn2+.

COMPARISON OF THE ANTITHROMBOTIC, ANTICLOTTING AND ANTIPLATELET AGGREGATORY ACTIVITIES OFLOW MOLECULAR WEIGHT RD HEPARIN WITH HEPARIN

1987 ◽  
Author(s):  
R L Fenichel ◽  
W Carmint ◽  
B Small ◽  
J Willis
Keyword(s):  
Human Platelet ◽  
Ex Vivo ◽  
Platelet Rich Plasma ◽  
Subcutaneous Administration ◽  
Factor Xa ◽  
Duration Of Action ◽  
Antithrombotic Activity ◽  
Significant Difference ◽  
Initial Comparison

An initial comparison of in vitro plasma anti-factor Xa (anti Xa) and activated partial thromboplastin time (APTT) values of RD heparin with heparin based upon USP units shows increased anti Xa and decreased APTT activity of RD heparin. An ex vivo experiment in rabbits in which 100 USP units/kg of RD heparinand 200 USP units/kg of heparin, when given by the subcutaneous route, reflects the significantly increased anti Xa activity generated by RD heparin as wellas its longer duration of action. No significant difference in APTT activity was observed for the two heparins, but an increased anti Xa/APTT ratio (greaterthan two) was observed for the RD heparin. Heparin (10 yg/ml), but not RD heparin, potentiated adenosinediphosphate (ADP) induced platelet aggregation in human platelet rich plasma. Subcutaneous administration of RD heparin or heparin to rabbits over the dosage range of 0.75 to 1.75 mg/kg gives similar mean dose response lines for these heparins in the thrombosis-stasis model as measured by the extent of jugular vein clotting. Administration of these heparins to rabbits on a USP unitage basis shows a significantly greater antithrombotic effect for RD heparin at 120 and 160 USP units/kg. Moreover, this experiment indicates that if the optimum dosage of 120 USP units/kgfor RD heparin is exceeded then we begin to see an indication of loss of antithrombotic activity.

A mathematical model of a bullfrog cardiac pacemaker cell

1990 ◽  
Vol 259 (2) ◽  
pp. H352-H369 ◽  
Author(s):  
R. L. Rasmusson ◽  
J. W. Clark ◽  
W. R. Giles ◽  
E. F. Shibata ◽  
D. L. Campbell
Keyword(s):  
Action Potential ◽  
Voltage Clamp ◽  
Binding Proteins ◽  
Single Cells ◽  
Cardiac Pacemaker ◽  
Ionic Currents ◽  
Tissue Type ◽  
Delayed Rectifier ◽  
Single Action ◽  
Diastolic Depolarization

Previous models of cardiac cellular electrophysiology have been based largely on voltage-clamp measurements obtained from multicellular preparations and often combined data from different regions of the heart and a variety of species. We have developed a model of cardiac pacemaking based on a comprehensive set of voltage-clamp measurements obtained from single cells isolated from one specific tissue type, the bullfrog sinus venosus (SV). Consequently, sarcolemmal current densities and kinetics are not influenced by secondary phenomena associated with multicellular preparations, allowing us to realistically simulate processes thought to be important in pacemaking, including the Na(+)-K+ pump and Na(+)-Ca2+ exchanger. The membrane is surrounded extracellularly by a diffusion-limited space and intracellularly by a limited myoplasmic volume containing Ca2(+)-binding proteins (calmodulin, troponin). The model makes several predictions regarding mechanisms involved in pacing. 1) Primary pacemaking cannot be attributed to any single current but arises from both the lack of a background K+ current and a complex interaction between Ca2+, delayed-rectifier K+, and background leak currents. 2) Ca2+ current displays complex behavior and is important during repolarization. 3) Because of Ca2+ buffering by myoplasmic proteins, the Na(+)-Ca2+ exchanger current is small and has little influence on action potential repolarization but may modulate the maximum diastolic potential. 4) The Na(+)-K+ pump current does not play an active role in repolarization but is of sufficient size to modulate the rate of diastolic depolarization. 5) K+ accumulation and Ca2+ depletion may occur in the extracellular spaces but play no role in either the diastolic depolarization or repolarization of a single action potential. This model illustrates the importance of basing simulations on quantitative measurements of ionic currents in myocytes and of including both electrogenic transporter mechanisms and Ca2+ buffering by myoplasmic Ca2(+)-binding proteins.

P2558PDE4 regulates cardiac pacemaker function

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
D Mika ◽  
A M Gomez ◽  
R Fischmeister ◽  
G Vandecasteele
Keyword(s):  
Cardiac Pacemaker ◽  
Hydrolytic Activity ◽  
Pde4 Inhibitor ◽  
Pacemaker Activity ◽  
Ventricular Cells ◽  
Pacemaker Function ◽  
S 100 ◽  
Beating Rate ◽  
Respective Contribution

Abstract Background Numerous epidemiological and clinical studies have revealed a positive correlation between heart rate (HR) and cardiovascular morbimortality. The autonomic nervous system is the major extracardiac determinant of HR. During sympathetic stimulation, the activation of β-adrenergic receptors (βAR) induces an increase in cAMP levels, leading to positive chronotropic effect. Among the 5 cardiac cAMP-PDE families, PDE4 is critical for controlling excitation-contraction coupling (ECC) during βAR stimulation in atrial and ventricular cells. PDE4 may also be important for automaticity. 3 genes encode for PDE4s: pde4a, pde4b, pde4d. Their respective contribution to the regulation of pacemaker activity remains ill-defined. Purpose Define the role of PDE4 isoforms in the regulation of cardiac pacemaker activity Methods Total PDE activity was determined in mouse sinoatrial node (SAN) tissue as the cAMP-hydrolytic activity measured in the absence of PDE inhibitor and the fraction corresponding to PDE4 activity was assessed by including the PDE4 inhibitor Ro-20-1724. The in vitro pacemaker activity was assessed by measuring spontaneous Ca2+ transients in Fluo4-loaded-SAN tissue. Images were obtained using confocal microscopy. Results Ro-20-1724 increased beating rate of intact SAN and increased PKA-phosphorylation of key ECC actors (ryanodine receptor, phospholamban and contractile proteins). PDE4 activity was found to account for 60% of the total cAMP-PDE activity in SAN (n=3 independent experiments). PDE4A, PDE4B and PDE4D isoforms were found to be expressed in mouse SAN (n=5 independent experiments). In PDE4D-, but not in PDE4B-deficient mice, Ca2+ homeostasis was altered in control conditions (ctrl) and after βAR stimulation with isoprenaline (iso). Indeed, ablation of PDE4D induced decreased beating rate (ctrl: 1.00±0.08 s–1 vs 1.57±0.05 s–1; iso: 1.71±0.17 s–1 vs 2.39±0.08 s–1, p<0.0001) and increased Ca2+ spark frequency (ctrl: 15.9±5.2 sparks/s/100 μm vs 1.9±0.4 sparks/s/100 μm; iso: 22.9±7.1 sparks/s/100 μm vs 0.6±0.2 sparks/s/100 μm, p<0.0001) (Figure). Calcium Homeostasis in SAN cells Conclusion PDE4 controls pacemaker function in mice and PDE4D ablation strongly perturbs normal SAN activity. Acknowledgement/Funding ANR, Fondation Lefoulon Delalande, CORDDIM

scholarly journals In Vitro Effect of Temperature on Dentin Bond Strength of Universal Adhesive Systems

2019 ◽  
pp. 253-261
Author(s):  
Serdar Akarsu DDS, PhD ◽  
Sultan Aktuğ Karademir DDS
Keyword(s):  
Bond Strength ◽  
Adhesive System ◽  
Effect Of Temperature ◽  
Single Bond ◽  
Adhesive Systems ◽  
Universal Adhesive ◽  
Significant Difference ◽  
Universal Adhesives ◽  
Vitro Effect

The aim of this study was to evaluate the shear bond strength (SBS) of two universal adhesives (Universal Single Bond and All Bond Universal) and a two-step self-etch adhesive system (Clearfil SE Bond) to dentine at various temperatures. Materials and Methods: One hundred and twenty dentin specimens were divided randomly to 12 groups, according to adhesive systems (Universal Single Bond and All Bond Universal, Clearfil SE Bond)  and temperature  ( 4ºC, 20 ºC, 36ºC, 55ºC) used. Dentin specimens were prepared (n :10, adhesives were applied, and composite cylinders were polymerized. Statistical analysis of the SBS data was performed using Two-way analysis of variance (ANOVA) and Tukey’s Honestly Significant Differences post-hoc test. Results: The Clearfil SE Bond was shown to have higher SBS than the universal adhesives at all temperatures; however, there was no statistically significant difference (P>0.05). In both groups, the lowest SBS values were observed in the samples at 4°C while the highest SBS values were observed in the samples at 55°C. In this case, there was a statistically significant difference (P<0.05). Conclusions: The results suggest that the effectiveness of an adhesive may increase if it is preheated at 36°C or above before use instead of being used immediately after removal from the refrigerator or at room temperature.

The development of dormancy in bulblets of Lilium speciosum generated in vitro. II. The effect of temperature

1990 ◽  
Vol 80 (3) ◽  
pp. 431-436 ◽  
Author(s):  
Isabelle Delvallee ◽  
Annie Paffen ◽  
Geert-Jan De Klerk
Keyword(s):  
Effect Of Temperature ◽  
Lilium Speciosum

Effect of Temperature on ADP-Induced Platelet Aggregation

1973 ◽  
Vol 29 (01) ◽  
pp. 183-189
Author(s):  
C. A Praga ◽  
E. M Pogliani
Keyword(s):  
Platelet Aggregation ◽  
Incubation Period ◽  
Room Temperature ◽  
Important Variable ◽  
Practical Significance ◽  
Effect Of Temperature ◽  
Induce Platelet Aggregation ◽  
Cuvette Holder ◽  
Exact Temperature

SummaryTemperature represents a very important variable in ADP-induced platelet aggregation.When low doses of ADP ( < 1 (μM) are used to induce platelet aggregation, the length of the incubation period of PRP in the cuvette holder of the aggregometer, thermostatted at 37° C, is very critical. Samples of the same PRP previously kept at room temperature, were incubated for increasing periods of time in the cuvette of the aggregometer before adding ADP, and a significant decrease of aggregation, proportional to the length of incubation, was observed. Stirring of the PRP during the incubation period made these changes more evident.To measure the exact temperature of the PRP during incubation in the aggre- gometer, a thermocouple device was used. While the temperature of the cuvette holder was stable at 37° C, the PRP temperature itself increased exponentially, taking about ten minutes from the beginning of the incubation to reach the value of 37° C. The above results have a practical significance in the reproducibility of the platelet aggregation test in vitro and acquire particular value when the effect of inhibitors of ADP induced platelet aggregation is studied.Experiments carried out with three anti-aggregating agents (acetyl salicyclic acid, dipyridamole and metergoline) have shown that the incubation conditions which influence both the effect of the drugs on platelets and the ADP breakdown in plasma must be strictly controlled.

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