Reloading of Ca(2+)-depleted sarcoplasmic reticulum during rest in guinea pig ventricular myocytes

1996 ◽  
Vol 271 (5) ◽  
pp. H1814-H1822 ◽  
Author(s):  
C. M. Terracciano ◽  
K. T. MacLeod
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Detection System ◽  
Rest Interval ◽  
Time Intervals ◽  
Rapid Cooling ◽  
Fluorescent Indicator ◽  
Resting Cell ◽  
Normal Tyrode Solution

The effects of rest on a Ca(2+)-depleted sarcoplasmic reticulum (SR) in guinea pig ventricular myocytes were investigated. Cell shortening was measured using a video edge-detection system, and cytoplasmic Ca2+ was monitored using the fluorescent indicator indo-1. Rapid cooling and rewarming in the presence of 10 mM caffeine were used to deplete the SR of Ca2+. The resting cell was then superfused for variable time intervals with a normal Tyrode solution containing 2 mM Ca2+. Another rapid cooling in caffeine was performed to assess the SR Ca2+ load at the end of rest. Rapid cooling after 1- and 2-min rest elicited an increase of indo-1 fluorescence of 51.9 +/- 7.7 (n = 17) and 72.7 +/- 6.7% of control (n = 9), respectively. This increase was not detectable when Ca2+ was absent from the superfusing solution. In contrast, the increase was larger when external Ca2+ was elevated to 4 mM. Nickel (5 mM) and nifedipine (20 microM) added to the superfusing solution during the rest interval did not alter the increase in indo-1 fluorescence. We conclude that Ca2+ is reaccumulated by a depleted SR during rest. Although this Ca2+ seems to originate from the extracellular space, its route from there to the SR is unclear.

scholarly journals Myocardial Depressant Effects of Desflurane

2007 ◽  
Vol 106 (5) ◽  
pp. 956-966 ◽  
Author(s):  
Wyun Kon Park ◽  
Myung Hee Kim ◽  
Duck Sun Ahn ◽  
Jee Eun Chae ◽  
Young Seok Jee ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Isometric Force ◽  
Peak Force ◽  
Papillary Muscles ◽  
Tyrode Solution ◽  
Rapid Cooling ◽  
K Current

Background The authors determined whether desflurane altered myocardial excitation-contraction coupling and electrophysiologic behavior in the same manner as isoflurane and sevoflurane. Methods The effects of desflurane on isometric force in guinea pig ventricular papillary muscles were studied in modified standard and in 26 mM K(+) Tyrode solution with 0.1 microm isoproterenol. Desflurane effects on sarcoplasmic reticulum Ca(2+) release were also determined by examining its actions on rat papillary muscles, guinea pig papillary muscles in low-Na(+) Tyrode solution, and rapid cooling contractures. Normal and slow action potentials were recorded using a conventional microelectrode technique. Ca(2+) and K(+) currents of guinea pig ventricular myocytes were examined. Results Desflurane (5.3% and 11.6%) decreased peak force to approximately 70% and 40% of the baseline, respectively, similar to the effects of equianesthetic isoflurane concentrations. With isoproterenol in 26 mM K(+) Tyrode solution, desflurane markedly depressed late peaking force and modestly depressed early peak force. The rested state contractions of rat myocardium or guinea pig myocardium in low-Na(+) Tyrode solution were modestly depressed, whereas rapid cooling contractures were virtually abolished after desflurane administration. Desflurane significantly prolonged the action potential duration. Desflurane reduced L-type Ca(2+) current and the delayed outward K(+) current but did not alter the inward rectifier K(+) current. Conclusions Myocardial depression by desflurane is due to decreased Ca(2+) influx, whereas depolarization-activated sarcoplasmic reticulum Ca(2+) release is modestly depressed, similar to the actions of isoflurane and sevoflurane. Desflurane depressed the delayed outward K(+) current associated with significant lengthening of cardiac action potentials.

scholarly journals Increases in diastolic [Ca2+] can contribute to positive inotropy in guinea pig ventricular myocytes in the absence of changes in amplitudes of Ca2+ transients

2006 ◽  
Vol 291 (4) ◽  
pp. H1623-H1634 ◽  
Author(s):  
Robin H. Shutt ◽  
Gregory R. Ferrier ◽  
Susan E. Howlett
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
High Resistance ◽  
Ventricular Myocytes ◽  
Edge Detector ◽  
Contraction Amplitude ◽  
Positive Inotropy ◽  
Resting Cell ◽  
Intracellular Ca ◽  
Isolated Ventricular Myocytes

Increases in contraction amplitude following rest or in elevated extracellular Ca2+ concentration ([Ca2+]) have been attributed to increased sarcoplasmic reticulum (SR) Ca2+ stores and/or increased trigger Ca2+. However, either manipulation also may elevate diastolic [Ca2+]. The objective of this study was to determine whether elevation of diastolic [Ca2+] could contribute to positive inotropy in isolated ventricular myocytes. Voltage-clamp experiments were conducted with high-resistance microelectrodes in isolated myocytes at 37°C. Intracellular free [Ca2+] was measured with fura-2, and cell shortening was measured with an edge detector. SR Ca2+ stores were assessed with 10 mM caffeine (0 mM Na+, 0 mM Ca2+). Following a period of rest, cells were activated with trains of pulses, which generated contractions of increasing amplitude, called positive staircases. Positive staircases were accompanied by increasing diastolic [Ca2+] but no change in Ca2+ transient amplitudes. When extracellular [Ca2+] was elevated from 2.0 to 5.0 mM, resting intracellular [Ca2+] increased and resting cell length decreased. Amplitudes of contractions and L-type Ca2+ current increased in elevated extracellular [Ca2+], although SR Ca2+ stores, assessed by rapid application of caffeine, did not increase. Although Ca2+ transient amplitude did not increase in 5.0 mM extracellular [Ca2+], diastolic [Ca2+] continued to increase with increasing extracellular [Ca2+]. These data suggest that increased diastolic [Ca2+] contributes to positive inotropy following rest or with increasing extracellular [Ca2+] in guinea pig ventricular myocytes.

Regulation of contraction and relaxation by membrane potential in cardiac ventricular myocytes

2000 ◽  
Vol 278 (5) ◽  
pp. H1618-H1626 ◽  
Author(s):  
Gregory R. Ferrier ◽  
Isabel M. Redondo ◽  
Cindy A. Mason ◽  
Cindy Mapplebeck ◽  
Susan E. Howlett
Keyword(s):  
Membrane Potential ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Release Mechanism ◽  
Fura 2 ◽  
Regulation Of Contraction ◽  
Contraction And Relaxation ◽  
Sustained Responses

Control of contraction and relaxation by membrane potential was investigated in voltage-clamped guinea pig ventricular myocytes at 37°C. Depolarization initiated phasic contractions, followed by sustained contractions that relaxed with repolarization. Corresponding Ca2+ transients were observed with fura 2. Sustained responses were ryanodine sensitive and exhibited sigmoidal activation and deactivation relations, with half-maximal voltages near −46 mV, which is characteristic of the voltage-sensitive release mechanism (VSRM) for sarcoplasmic reticulum Ca2+. Inactivation was not detected. Sustained responses were insensitive to inactivation or block of L-type Ca2+ current ( I Ca-L). The voltage dependence of sustained responses was not affected by changes in intracellular or extracellular Na+ concentration. Furthermore, sustained responses were not inhibited by 2 mM Ni2+. Thus it is improbable that I Ca-L or Na+/Ca2+ exchange generated these sustained responses. However, rapid application of 200 μM tetracaine, which blocks the VSRM, strongly inhibited sustained contractions. Our study indicates that the VSRM includes both a phasic inactivating and a sustained noninactivating component. The sustained component contributes both to initiation and relaxation of contraction.

Rapid cooling contractures as an index of sarcoplasmic reticulum calcium content in rabbit ventricular myocytes

1989 ◽  
Vol 257 (5) ◽  
pp. H1369-H1377 ◽  
Author(s):  
L. V. Hryshko ◽  
V. Stiffel ◽  
D. M. Bers
Keyword(s):  
Electrical Stimulation ◽  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Calcium Content ◽  
Isometric Tension ◽  
Free Solution ◽  
Rapid Cooling ◽  
Rabbit Ventricular Myocytes ◽  
Sarcoplasmic Reticulum Calcium

Rapid cooling contractures (RCCs) were used to assess changes in sarcoplasmic reticulum (SR) Ca content in both isolated rabbit ventricular myocytes and multicellular preparations. The main difference observed between these preparations was the magnitude of RCCs relative to twitches, apparently due to differences in measured parameters, i.e., unloaded shortening vs. isometric tension. When multicellular preparations were unloaded, RCC shortening was similar to that observed in myocytes. RCC magnitude decreased as the time between the last electrical stimulation and the RCC was increased (rest decay). RCC rest decay closely paralleled that of postrest twitches, suggesting that SR Ca loss is responsible for this process. Paired RCC experiments were used to investigate RCC relaxation and rest decay. When a second RCC (RCC2) was induced immediately after the first (RCC1), a large contracture was still observed (RCC2/RCC1 x 100 = 77.8 +/- 7.3%, mean +/- SD), indicating that the SR resequestered the majority of Ca on rewarming. This fraction was increased (to 92.9 +/- 5.5%) if Na and Ca-free solution was used during RCCs and rewarming, indicating that Na-Ca exchange also contributes to RCC relaxation. Increasing the interval between paired RCCs led to a decrease in RCC2, analogous to rest decay. This rest decay was abolished by inhibiting Na-Ca exchange, indicating that SR Ca loss during rest is mediated primarily by this process. RCCs were abolished by 10 mM caffeine. Ryanodine (1 microM) greatly accelerated RCC rest decay but had less effect on RCCs generated immediately after a train of stimulation. This accelerated rest decay was also dependent on Na-Ca exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Myocardial Depressant Effects of Sevoflurane

1996 ◽  
Vol 84 (5) ◽  
pp. 1166-1176 ◽  
Author(s):  
Wyun Kon Park ◽  
Joseph J. Pancrazio ◽  
Chang Kook Suh ◽  
Carl III Lynch
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Action Potential ◽  
Papillary Muscle ◽  
Action Potential Duration ◽  
Action Potentials ◽  
Peak Force ◽  
Rapid Cooling ◽  
K Current ◽  
Slow Action Potentials

Background The effects of anesthetic concentrations of sevoflurane were studied in isolated myocardial tissue to delineate the mechanisms by which cardiac function is altered. Methods Isometric force of isolated guinea pig ventricular papillary muscle was studied at 37 degrees C in normal and 26 mM K+ Tyrode's solution at various stimulation rates. Normal and slow action potentials were evaluated using conventional microelectrodes. Effects of sevoflurane on sarcoplasmic reticulum function in situ were also evaluated by its effect on rapid cooling contractures, which are known to activate Ca2+ release from the sarcoplasmic reticulum, and on concentrations of rat papillary muscle. Finally, Ca2+ and K+ currents of isolated guinea pig ventricular myocytes were examined using the whole-cell patch clamp technique. Results Sevoflurane equivalent to 1.4% and 2.8% depressed guinea pig myocardial contractions to approximately 85 and approximately 65% of control, respectively, although the maximum rate of force development at 2 or 3 Hz and force in rat myocardium after rest showed less depression. In the partially depolarized, beta-adrenergically stimulated myocardium, sevoflurane selectively depressed late peak force without changing early peak force, whereas it virtually abolished rapid cooling contractures. Sevoflurane did not alter the peak amplitude or maximum depolarization rate of normal and slow action potentials, but action potential duration was significantly prolonged. In isolated guinea pig myocytes at room temperature, 0.7 mM sevoflurane (equivalent to 3.4%) depressed peak Ca2+ current by approximately 25% and increased the apparent rate of inactivation. The delayed outward K+ current was markedly depressed, but the inwardly rectifying K+ current was only slightly affected by 0.35 mM sevoflurane. Conclusions These results suggest that the direct myocardial depressant effects of sevoflurane are similar to those previously described for isoflurane. The rapid initial release of Ca2+ from the sarcoplasmic reticulum is not markedly decreased, although certain release pathway, specifically those induced by rapid cooling, appear to be depressed. Contractile depression may be partly related to the depression of Ca2+ influx through the cardiac membrane. The major electrophysiologic effect of sevoflurane seems to be a depression of the delayed outward K+ current, which appears to underlie the increased action potential duration.

Direct Myocardial Depressant Effect of Methylmethacrylate Monomer

2003 ◽  
Vol 98 (5) ◽  
pp. 1186-1194 ◽  
Author(s):  
Ki Jun Kim ◽  
Da Guang Chen ◽  
Namsik Chung ◽  
Carl Lynch ◽  
Wyun Kon Park
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Patch Clamp ◽  
Guinea Pig ◽  
Papillary Muscle ◽  
Peak Force ◽  
Maximal Rate ◽  
Tyrode Solution ◽  
Depressant Effect ◽  
Rapid Cooling ◽  
Force Development

Background The present study explored the mechanism of direct myocardial depression by methylmethacrylate monomer (MMA). Methods Isometric contraction of isolated guinea pig right ventricular papillary muscle was measured in modified normal and 26 mm K+ Tyrode solutions at various stimulation rates. Normal and slow action potentials were evaluated by conventional microelectrode technique. MMA effects on various aspects of sarcoplasmic reticulum function were evaluated by its effect on rapid-cooling contractures, rested-state contraction in rat papillary muscle in modified normal Tyrode solution, and in guinea pig papillary muscle under low Na+ (25 mm) Tyrode solution. Whole cell patch clamp techniques were applied to measure the inward Ca2+ currents (I(Ca)). Results MMA (0.5, 1.5, and 4.7 mm) caused concentration-dependent depression of peak force and maximal rate of force development to approximately 70, 50, and 20% of baseline from rested state to 3 Hz stimulation rates, respectively. Depression of peak force and maximal rate of force development by MMA was dependent on stimulation frequency, with less depression at higher stimulation rates. In low Na+ Tyrode solution, 1.5 mm MMA depressed peak force of rat and guinea pig myocardium by 20-30%. In 26 mm K+ Tyrode solution, 0.5 and 1.5 mm MMA caused selective and marked concentration-dependent depression of late force development (0.5 mm: approximately 60% of baseline, 1.5 mm: approximately 30% of baseline) with no alteration in early force development. MMA (1.5 mm) depressed rapid-cooling contracture to 53 +/- 10% of baseline, accompanied by approximately 63% prolongation of time to peak contracture. In patch clamp studies, MMA reduced I(Ca) in a concentration-dependent manner. Conclusions The direct myocardial depressant effect of MMA seems to be caused in part by depression of Ca2+ influx through cardiac membrane, while depolarization-activated sarcoplasmic reticulum Ca2+ release appears modestly depressed.

Na-independent Cl(-)-HCO3- exchange mediates recovery of pHi from alkalosis in guinea pig ventricular myocytes

1994 ◽  
Vol 267 (1) ◽  
pp. H85-H91 ◽  
Author(s):  
P. Xu ◽  
K. W. Spitzer
Keyword(s):  
Guinea Pig ◽  
Intracellular Ph ◽  
Ventricular Myocytes ◽  
Initial Rate ◽  
Ph Sensitive ◽  
Disulfonic Acid ◽  
Weak Base ◽  
External Application ◽  
Fluorescent Indicator ◽  
Ethanesulfonic Acid

The pH-sensitive fluorescent indicator, carboxy-seminaphthorhodafluor 1 (SNARF 1) was used to assess the contribution of forward Na-independent Cl(-)-HCO3- exchange (1 external Cl- exchanged for 1 internal HCO3-) to intracellular pH (pHi) recovery from alkalosis in adult ventricular myocytes (guinea pig). Intracellular alkalosis was elicited by external application of the weak base, trimethylamine. In the absence of CO2-HCO3- (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solution) the initial rate of pHi recovery from alkalosis (pHi = 7.25-7.75) was slow and independent of pHi, yielding an apparent net HCO3- efflux of 0.36 +/- 0.11 mM/min. In CO2-HCO3(-)-buffered solution, the initial rate of pHi recovery and net HCO3- efflux were much faster and markedly increased by raising pHi. At pHi approximately 7.25, net HCO3- efflux was approximately 2 mM/min and rose to 9 mM/min at pHi approximately 7.6. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (0.4 mM) decreased net HCO3- efflux by 78.1 +/- 8.9% in CO2-HCO3(-)-buffered solution. Reduction in extracellular Cl- concentration from 135 to 20 mM markedly slowed the rate of pHi recovery from alkalosis and reduced net HCO3- efflux. pHi recovery from alkalosis was unaffected by removal of external sodium or exposure to 1 mM amiloride. These results indicate that forward Na-independent Cl(-)-HCO3- exchange mediates pHi recovery from alkalosis in guinea pig ventricular myocytes.

Sign in / Sign up

Export Citation Format

Share Document