Excitation–contraction coupling in isolated adult ventricular myocytes from the rat, dog, and rabbit: effects of various inotropic interventions in the presence of ryanodine

1986 ◽  
Vol 64 (12) ◽  
pp. 1473-1483 ◽  
Author(s):  
Magda Horackova
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Inotropic Agents ◽  
Inhibitory Effects ◽  
Pharmacological Interventions ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Ventricular Cells ◽  
Contractile Activation ◽  
Dog Myocytes

Enzymatically isolated ventricular cells from rats, dogs, and rabbits were electrically stimulated and their membrane potentials were recorded simultaneously with their contractions. Specific pharmacological interventions were used to assess the relative roles of transsarcolemmal Ca2+ entry and the Ca2+ release by the sarcoplasmic reticulum in activating contractions, in these myocytes. We used ryanodine and caffeine to influence Ca2+ release by the sarcoplasmic reticulum, BAY K 8644 and epinephrine to increase Ca2+ entry through Ca2+ channels, and veratridine, ouabain, and monensin to increase Ca2+ entry through Na+–Ca2+ exchange. Ryanodine (1 μM) completely inhibited the shortenings in rat and dog myocytes, but the contractions in rabbit myocytes were much less sensitive to this alkaloid. Similar inhibitory effects of ryanodine were observed in the presence of various inotropic agents with two exceptions: caffeine's effect on the dog myocytes was relatively insensitive to ryanodine and the long-lasting tonic contractions that veratridine triggered in the myocytes of all three species remained completely unaffected by ryanodine. The data indicate that contractile activation in rat and dog ventricular cells is strongly dependent on Ca2+ release from the sarcoplasmic reticulum, while contractility in rabbit myocytes seems to be more dependent on Ca2+ entry through the sarcolemma. The ryanodine-resistant tonic contractions triggered in the myocytes of all three species in the presence of veratridine may be activated by an increased Ca2+ entry via Na+–Ca2+ exchange.

Differential Effects of Fentanyl and Morphine on Intracellular Ca2+Transients and Contraction in Rat Ventricular Myocytes 

1998 ◽  
Vol 89 (6) ◽  
pp. 1532-1542 ◽  
Author(s):  
Noriaki Kanaya ◽  
Daniel R. Zakhary ◽  
Paul A. Murray ◽  
Derek S. Damron
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Myocardial Contractility ◽  
Ventricular Myocytes ◽  
Free Acid ◽  
Intact Cells ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Rat Ventricular Myocytes ◽  
Fura 2 ◽  
Cardiac Excitation

Background Our objective was to elucidate the direct effects of fentanyl and morphine on cardiac excitation-contraction coupling using individual, field-stimulated rat ventricular myocytes. Methods Freshly isolated myocytes were loaded with fura-2 and field stimulated (0.3 Hz) at 28 degrees C. Amplitude and timing of intracellular Ca2+ concentration (at a 340:380 ratio) and myocyte shortening (video edge detection) were monitored simultaneously in individual cells. Real time Ca2+ uptake into isolated sarcoplasmic reticulum vesicles was measured using fura-2 free acid in the extravesicular compartment. Results The authors studied 120 cells from 30 rat hearts. Fentanyl (30-1,000 nM) caused dose-dependent decreases in peak intracellular Ca2+ concentration and shortening, whereas morphine (3-100 microM) decreased shortening without a concomitant decrease in the Ca2+ transient. Fentanyl prolonged the time to peak and to 50% recovery for shortening and the Ca2+ transient, whereas morphine only prolonged the timing parameters for shortening. Morphine (100 microM), but not fentanyl (1 microM), decreased the amount of Ca2+ released from intracellular stores in response to caffeine in intact cells, and it inhibited the rate of Ca2+ uptake in isolated sarcoplasmic reticulum vesicles. Fentanyl and morphine both caused a downward shift in the dose-response curve to extracellular Ca2+ for shortening, with no concomitant effect on the Ca2+ transient. Conclusions Fentanyl and morphine directly depress cardiac excitation-contraction coupling at the cellular level. Fentanyl depresses myocardial contractility by decreasing the availability of intracellular Ca2+ and myofilament Ca2+ sensitivity. In contrast, morphine depresses myocardial contractility primarily by decreasing myofilament Ca2+ sensitivity.

scholarly journals Ca2+ cycling in cardiomyocytes from a high-performance reptile, the varanid lizard (Varanus exanthematicus)

2009 ◽  
Vol 297 (6) ◽  
pp. R1636-R1644 ◽  
Author(s):  
Gina L. J. Galli ◽  
Daniel E. Warren ◽  
Holly A. Shiels
Keyword(s):  
Sarcoplasmic Reticulum ◽  
High Performance ◽  
Time Course ◽  
Ventricular Myocytes ◽  
Volume Ratio ◽  
Voltage Sensitivity ◽  
Excitation Contraction Coupling ◽  
Electrophysiological Properties ◽  
Contraction Coupling ◽  
Cardiovascular Performance

The varanid lizard possesses one of the largest aerobic capacities among reptiles with maximum rates of oxygen consumption that are twice that of other lizards of comparable sizes at the same temperature. To support this aerobic capacity, the varanid heart possesses morphological adaptations that allow the generation of high heart rates and blood pressures. Specializations in excitation-contraction coupling may also contribute to the varanids superior cardiovascular performance. Therefore, we investigated the electrophysiological properties of the l-type Ca2+ channel and the Na+/Ca2+ exchanger (NCX) and the contribution of the sarcoplasmic reticulum to the intracellular Ca2+ transient (Δ[Ca2+]i) in varanid lizard ventricular myocytes. Additionally, we used confocal microscopy to visualize myocytes and make morphological measurements. Lizard ventricular myocytes were found to be spindle-shaped, lack T-tubules, and were ∼190 μm in length and 5–7 μm in width and depth. Cardiomyocytes had a small cell volume (∼2 pL), leading to a large surface area-to-volume ratio (18.5), typical of ectothermic vertebrates. The voltage sensitivity of the l-type Ca2+ channel current ( ICa), steady-state activation and inactivation curves, and the time taken for recovery from inactivation were also similar to those measured in other reptiles and teleosts. However, transsarcolemmal Ca2+ influx via reverse mode Na+/Ca2+ exchange current was fourfold higher than most other ectotherms. Moreover, pharmacological inhibition of the sarcoplasmic reticulum led to a 40% reduction in the Δ[Ca2+]i amplitude, and slowed the time course of decay. In aggregate, our results suggest varanids have an enhanced capacity to transport Ca2+ through the Na+/Ca2+ exchanger, and sarcoplasmic reticulum suggesting specializations in excitation-contraction coupling may provide a means to support high cardiovascular performance.

Frog ventricle: participation of SR in excitation-contraction coupling

1989 ◽  
Vol 256 (5) ◽  
pp. H1432-H1439
Author(s):  
M. E. Anderson ◽  
I. J. Fox ◽  
C. R. Swayze ◽  
S. K. Donaldson
Keyword(s):  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Inhibitory Effects ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Resting Tension ◽  
Mammalian Myocardium ◽  
Frog Myocardium ◽  
Frog Ventricle ◽  
Important Site

Activation of the first beat (B1) following a 60-s pause is diminished in isometrically contracting frog ventricular strips, in contrast to the augmentation documented for sarcoplasmic reticulum (SR)-dependent mammalian myocardium. However, treatment of frog ventricular strips with ouabain, an indirect inhibitor of the sarcolemmal Na+-Ca2+ exchanger, selectively enhanced postpause beats suggesting that in the absence of ouabain significant extrusion of cellular Ca2+ occurred during the pause. Because resting tension did not increase during the pause in ouabain-treated strips, the nonextruded Ca2+ must have been sequestered into a compartment such as SR. Steady-state beats were not affected by ouabain; its actions appeared to be separate from its known positive inotropism. Caffeine, a direct SR stimulus, initially enhanced B1 and subsequently decreased activation of all beats, which was consistent with initial augmentation of SR Ca2+ release and subsequent depletion of SR Ca2+ stores. Ouabain both potentiated the stimulatory effects and blocked the inhibitory effects of caffeine, suggesting that ouabain increased Ca2+ stores in the same intracellular Ca2+ pool as that acted on by caffeine, the SR. Ryanodine, an inhibitor of SR in mammalian myocardium, did not affect activation of frog myocardium. SR may be an important site for activator Ca2+ cycling in frog myocardium under control conditions as well as after long diastolic intervals in the presence of ouabain.

Photoperiod-dependent modulation of cardiac excitation contraction coupling in the Siberian hamster

2005 ◽  
Vol 288 (3) ◽  
pp. R607-R614 ◽  
Author(s):  
K. M. Dibb ◽  
C. L. Hagarty ◽  
A. S. I. Loudon ◽  
A. W. Trafford
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Prolonged Exposure ◽  
Ventricular Myocytes ◽  
Short Photoperiod ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Excitation Contraction Coupling ◽  
Siberian Hamster ◽  
Contraction Coupling ◽  
Single Ventricular Myocytes ◽  
Cardiac Excitation

In mammals, changes in photoperiod regulate a diverse array of physiological and behavioral processes, an example of which in the Siberian hamster ( Phodopus sungorus) is the expression of bouts of daily torpor following prolonged exposure to a short photoperiod. During torpor, body temperature drops dramatically; however, unlike in nonhibernating or nontorpid species, the myocardium retains the ability to contract and is resistant to the development of arrhythmias. In the present study, we sought to determine whether exposure to a short photoperiod results in alterations to cardiac excitation-contraction coupling, thus potentially enabling the heart to survive periods of low temperature during torpor. Experiments were performed on single ventricular myocytes freshly isolated from the hearts of Siberian hamsters that had been exposed to either 12 wk of short-day lengths (SD) or 12 wk of long-day lengths (LD). In SD-acclimated animals, the amplitude of the systolic Ca2+ transient was increased (e.g., from 142 ± 17 nmol/l in LD to 229 ± 31 nmol/l in SD at 4 Hz; P < 0.001). The increased Ca2+ transient amplitude in the SD-acclimated animals was not associated with any change in the shape or duration of the action potential. However, sarcoplasmic reticulum Ca2+ content measured after current-clamp stimulation was increased in the SD-acclimated animals (at 4 Hz, 110 ± 5 vs. 141 ± 15 μmol/l, P < 0.05). We propose that short photoperiods reprogram the function of the cardiac sarcoplasmic reticulum, resulting in an increased Ca2+ content, and that this may be a necessary precursor for maintenance of cardiac function during winter torpor.

scholarly journals High [Na+]i in cardiomyocytes from rainbow trout

2007 ◽  
Vol 293 (2) ◽  
pp. R861-R866 ◽  
Author(s):  
Rikke Birkedal ◽  
Holly A. Shiels
Keyword(s):  
Rainbow Trout ◽  
Ventricular Myocytes ◽  
Resting Cells ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Contraction Frequency ◽  
Reverse Mode ◽  
Whole Cell Patch Clamp ◽  
Ventricular Cells

Intracellular Na+-concentration, [Na+]i modulates excitation-contraction coupling of cardiac myocytes via the Na+/Ca2+ exchanger (NCX). In cardiomyocytes from rainbow trout ( Oncorhyncus mykiss), whole cell patch-clamp studies have shown that Ca2+ influx via reverse-mode NCX contributes significantly to contraction when [Na+]i is 16 mM but not 10 mM. However, physiological [Na+]i has never been measured. We recorded [Na+]i using the fluorescent indicator sodium-binding benzofuran isophthalate in freshly isolated atrial and ventricular myocytes from rainbow trout. We examined [Na+]i at rest and during increases in contraction frequency across three temperatures that span those trout experience in nature (7, 14, and 21°C). Surprisingly, we found that [Na+]i was not different between atrial and ventricular cells. Furthermore, acute temperature changes did not affect [Na+]i in resting cells. Thus, we report a resting in vivo [Na+]i of 13.4 mM for rainbow trout cardiomyocytes. [Na+]i increased from rest with increases in contraction frequency by 3.2, 4.7, and 6.5% at 0.2, 0.5, and 0.8 Hz, respectively. This corresponds to an increase of 0.4, 0.6, and 0.9 mM at 0.2, 0.5, and 0.8 Hz, respectively. Acute temperature change did not significantly affect the contraction-induced increase in [Na+]i. Our results provide the first measurement of [Na+]i in rainbow trout cardiomyocytes. This surprisingly high [Na+]i is likely to result in physiologically significant Ca2+ influx via reverse-mode NCX during excitation-contraction coupling. We calculate that this Ca2+-source will decrease with the action potential duration as temperature and contraction frequency increases.

Overexpression of human β2-adrenergic receptors increases gain of excitation-contraction coupling in mouse ventricular myocytes

2004 ◽  
Vol 287 (3) ◽  
pp. H1029-H1038 ◽  
Author(s):  
Scott A. Grandy ◽  
Eileen M. Denovan-Wright ◽  
Gregory R. Ferrier ◽  
Susan E. Howlett
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Action Potential ◽  
Adrenergic Receptors ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Wild Type ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Cardiac Excitation ◽  
Action Potential Configuration

This study investigated cardiac excitation-contraction coupling at 37°C in transgenic mice with cardiac-specific overexpression of human β2-adrenergic receptors (TG4 mice). In field-stimulated myocytes, contraction was significantly greater in TG4 compared with wild-type (WT) ventricular myocytes. In contrast, when duration of depolarization was controlled with rectangular voltage clamp steps, contraction amplitudes initiated by test steps were the same in WT and TG4 myocytes. When cells were voltage clamped with action potentials simulating TG4 and WT action potential configurations, contractions were greater with long TG4 action potentials and smaller with shorter WT action potentials, which suggests an important role for action potential configuration. Interestingly, peak amplitude of L-type Ca2+ current ( ICa-L) initiated by rectangular test steps was reduced, although the voltage dependencies of contractions and currents were not altered. To explore the basis for the altered relation between contraction and ICa-L, Ca2+ concentrations were measured in myocytes loaded with fura 2. Diastolic concentrations of free Ca2+ and amplitudes of Ca2+ transients were similar in voltage-clamped myocytes from WT and TG4 mice. However, sarcoplasmic reticulum (SR) Ca2+ content assessed with the rapid application of caffeine was elevated in TG4 cells. Increased SR Ca2+ was accompanied by increased frequency and amplitudes of spontaneous Ca2+ sparks measured at 37°C with fluo 3. These observations suggest that the gain of Ca2+-induced Ca2+ release is increased in TG4 myocytes. Increased gain counteracts the effects of decreased amplitude of ICa-L in voltage-clamped myocytes and likely contributes to increased contraction amplitudes in field-stimulated TG4 myocytes.

Thiopental Alters Contraction, Intracellular Ca2+, and pH in Rat Ventricular Myocytes 

1998 ◽  
Vol 89 (1) ◽  
pp. 202-214 ◽  
Author(s):  
Noriaki Kanaya ◽  
Daniel R. Zakhary ◽  
Paul A. Murray ◽  
Derek S. Damron
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Intracellular Ph ◽  
Ventricular Myocytes ◽  
Negative Inotropic Effect ◽  
Inotropic Effect ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Rat Ventricular Myocytes ◽  
Fura 2 ◽  
Cardiac Excitation

Background Myocardial contractility is regulated by intracellular concentration of free Ca2+ ([Ca2'],) and myofilament Ca2+ sensitivity. The objective of this study was to elucidate the direct effects of thiopental on cardiac excitation-contraction coupling using individual, field-stimulated ventricular myocytes. Methods Freshly isolated rat ventricular myocytes were loaded with the Ca2+ indicator, fura-2, and placed on the stage of an inverted fluorescence microscope in a temperature-regulated bath. [Ca2+], (340/380 ratio) and myocyte shortening (video-edge detection) were monitored simultaneously in individual cells field-stimulated at 0.3 Hz. Amplitude and timing of myocyte shortening and [Ca2+l, were compared before and after addition of thiopental. Intracellular pH was measured with the pH indicator, BCECF (500/440 ratio). Real-time uptake of Ca2+ into isolated sarcoplasmic reticulum vesicles was measured using fura-2 free acid in the extravesicular compartment. One hundred thirty-two cells were studied. Results Field stimulation increased [Ca2+]i from 85 + 10 nM to 355 + 22 nM (mean + SEM). Myocytes shortened by 10% of resting cell length (127 + 5 tlm). Times to peak [Ca2+], and shortening were 139 + 6 and 173 + 7 msec, respectively. Times to 50% recovery for [Ca2+], and shortening were 296 + 6 and 290 + 6 ms, respectively. Addition of thiopental (30-1,000 /lM) resulted in dose-dependent decreases in peak [Ca2+]i and myocyte shortening. Thiopental altered time to peak and time to 50% recovery for [Ca2+], and myocyte shortening and inhibited the rate of uptake of Ca2+ into isolated sarcoplasmic reticulum vesicles. Thiopental did not, however, alter the amount of Ca2+ released in response to caffeine in sarcoplasmic reticulum vesicles or intact cells. Thiopental (100 uM) increased intracellular pH and caused an upward shift in the dose-response curve to extracellular Ca2+ for shortening, with no concomitant effect on peak [Ca2+],. These effects were abolished by ethylisopropyl amiloride, an inhibitor of Na+-H+ exchange. Conclusion Thiopental has a direct negative inotropic effect on cardiac excitation-contraction coupling at the cellular level, which is mediated by a decrease in [Ca2+],. Thiopental also increases myofilament Ca2+ sensitivity via alkalinization of the cell, which may partially offset its negative inotropic effect.

Cellular Basis for the Acute Inhibitory Effects of IL-6 and TNF- α on Excitation-contraction Coupling

1999 ◽  
Vol 31 (8) ◽  
pp. 1457-1467 ◽  
Author(s):  
Kazuro Sugishita ◽  
Koh-ichiro Kinugawa ◽  
Tatsuya Shimizu ◽  
Kazumasa Harada ◽  
Hiroshi Matsui ◽  
...  
Keyword(s):  
Inhibitory Effects ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Cellular Basis ◽  
Tnf Α
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