Recent reports revealed that the Na+/-Ca2+ exchangers and feet structures of sarcoplasmic reticulum (SR) are located in close vicinity in the specific compartment. Therefore, we investigated the possibility that the Na+/-Ca2+ exchanger may decrease the tension development by transporting the Ca2+ out of the cell right after it released from SR, on the basis of this anatomical proximity. We examined the negative force-frequency relationship of the developed tension in the electrically field stimulated left atria of postnatal developing rat (1, 3 day, 1 week and 4 week old after birth). Cyclopiazonic acid (3 X 10(-5) M) treatment decreased the developed tension further according to postnatal age. Monensin (3 X 10(-6) M) treatment did not increase the maximal tension in 4 week-old rat, preserving negative staircase, while the negative staircase in the younger rat were flattened. Ca2+ depletion in the buffer elicited more suppression of the maximal tension according to the frequency in all groups except the 4 week-old group. The % decrease of the maximal developed tension of 4 week-old group at 1 Hz to that of 0.1 Hz after Na+ and Ca2+ depletion was only a half of those of the younger groups. Taken together, it is concluded that the Na+/-Ca2+ exchange transports more Ca2+ released from SR out of the cell in proportion to the frequency, and this is responsible for the negative staircase effect of the rat heart.
Animals ; Foot ; Heart* ; Monensin ; Rats* ; Sarcoplasmic Reticulum

The effects of nifedipine, a dihydropyridine Ca2+ antagonist, on the eleetrically-evoked twitch response, train-of-four and tetanic stimulation were studied in the isolated rat hemidiaphragm preparation. Nifedipine, in concentrations ranging from 3 to 100 uM, increased the electrically-evoked (nerve stimulation, 0.1 Hz, 0.5 ms, 10 V) twitch response and train-of-four ratio in a dose-relat- ed fashion, and the potentiating effects were inhibited by d-tubocurarine preteratment. The effect of nifedipine was not affected by reducing the extracellular Ca2+ concentration from 2.5 mM to 1.25 mM. In cases of the direct(muscle, 0.1 Hz, 5 ms, 10 V) stimulation, nifedipine increased the twitch response in a dose-dependent manner, but the amplitudes were smaller than those in indirect stimulation. Nifedipine 30 uM potentiated the contractile response induced by 70 mM KC1 and caffeine(10 mM)-induced isometric contractile responses were markedly potentiated by nifedipine treatmeat. Nifedipine 70 upotentiated the effect of l mM caffeine on the electrically-evoked twitch response and the potentiating effect was also seen in reverse treatment. On the basis of these findings, the result of present study suggests that the potentiating contractile response by nifedipine is mediated by two distinctive mechanisms. One is the acetylcholine release from presynaptic nerve terminal and the other may be due to the releases of Ca2+ in sarcoplasmic reticulum.
Acetylcholine ; Animals ; Caffeine ; Nifedipine* ; Rats* ; Sarcoplasmic Reticulum ; Tubocurarine

No abstract available.
Muscle, Skeletal* ; Ryanodine Receptor Calcium Release Channel* ; Ryanodine* ; Sarcoplasmic Reticulum*

In order to elucidate the molecular mechanism of the intracellular Ca2+ overload frequently reported from diabetic heart, diabetic rats were induced by the administration of streptozotocin, the membrane vesicles of junctional SR (heavy SR, HSR) were isolated from the ventricular myocytes, and SR Ca2+ uptake and SR Ca2+ release were measured. The activity of SR Ca2+-ATPase was 562 +/- 14 nmol/min/mg protein in control heart. The activity was decreased to 413 +/- 30 nmol/min/mg protein in diabetic heart and it was partially recovered to 485 +/- 18 nmol/min/mg protein in insulin-treated diabetic heart. A similar pattern was observed in SR 45Ca2+ uptakes; the specific uptake was the highest in control heart and it was the lowest in diabetic heart. In SR 45Ca2+ release experiment, the highest release, 45% of SR 45Ca2+, was observed in control heart. The release of diabetic heart was 20% and it was 30% in insulin-treated diabetic heart. Our results showed that the activitiesof both SR Ca2+-ATPase and SR Ca2+ release channel were decreased in diabetic heart. In order to evaluate how these two factors contribute to SR Ca2+ storage, the activity of SR Ca2+-ATPase was measured in the uncoupled leaky vesicles. The uncoupling effect which is able to increase the activity of SR Ca2+-ATPase was observed in control heart; however, no significant increments of SR Ca2+-ATPase activities were measured in both diabetic and insulin-treated diabetic rats. These results represent that the Ca2+ storage in SR is significantly depressed and, therefore, Ca2+-sequestering activity of SR may be also depressed in diabetic heart.
Animals ; Heart ; Membranes ; Muscle Cells ; Rats* ; Sarcoplasmic Reticulum* ; Streptozocin

The underlying mechanism commonly applicable for both the positive and negative force-frequency relationships (FFR) was pursued in left atria (LA) of rat and rabbit. The species differences in the roles of Na+/Ca2+ exchanger and sarcoplasmic reticulum (SR), which are major intracellular Ca2+ regulatory mechanisms in the heart, were examined in the amplitude accommodation to the frequency that changed from 3 Hz to the variable test frequencies for 5 minutes in the electrically field stimulated left atria (LA) of rat and rabbit. Norepinephrine strongly increased the frequency-related amplitude accommodation in both of rat and rabbit LA, while monensin, oubain or the reduced Na+ and 0 mM Ca2+ containing Tyrode solution increased the frequency-related amplitude accommodation only in the rabbit LA. Monenisn was also able to increase the frequency-related amplitude accommodation only in 1-day old rat LA but not in 4-week old rat LA that had 75% less Na+/Ca2+ exchanger with 97% higher SR than 1-day old rat LA. Taken together, it is concluded that the differences in the prevalence between myocardial Na+/Ca2+ exchanger and SR in the amplitude accommodation to the frequency-change determine the difference in the FFR between rat and rabbit heart.
Animals ; Heart ; Monensin ; Norepinephrine ; Prevalence ; Rats* ; Sarcoplasmic Reticulum

This study is to investigate the mechanism of inhibitory effect of imipramine on the calcium utilization in single cells isolated from canine detrusor. 2 mm thick smooth muscle chops were incubated in 0.12% collagenase solution at 36degreeC, and aerated with 95% O2/5% CO2, and then cell suspension was examined Acetylcholine (ACh) evoked a concentration-dependent contraction of the isolated detrusor cells in normal physiologic salt solution (PSS), and the ACh-induced contraction was significantly inhibited by imipramine. In Ca2+-free PSS, ACh-induced contraction was less than those in normal PSS and it was not affected by the pretreatment with imipramine. Ca2+-induced contraction in Ca2+-free PSS was supressed by imipramine, but addition of A 23187, a calcium ionophore, overcomed the inhibitory effect of imipramine. High potassium-depolarization (40 mM KCl) evoked cell contraction, which was inhibited by imipramine. Caffeine, a releasing agent of the stored Ca2+ from sarcoplasmic reticulum, evoked a contraction of the cells that was not blocked by the pretreatment with imipramine. These results suggest that imipramine inhibits the influx of calcium in the detrusor cells through both the receptor-operated- and voltage-gated-calcium channels, but does not affect the release of calcium from intracellular storage site.
Acetylcholine ; Caffeine ; Calcimycin ; Calcium* ; Collagenases ; Imipramine* ; Muscle, Smooth ; Sarcoplasmic Reticulum

Using lipid bilayer reconstitution technique, we investigated the oxidation effect of t-butyl hydrogen peroxide (tBHP) on the single channel activity of the sarcoplasmic reticulum (SR) calcium release channels isolated from canine latissimus dorsi muscles. When 0.7% tBHP was added in the cytosolic side, the channel activity became suppressed (n = 7), and it was recovered by changing the solution to the control solution. The suppression was due to the change in the gating mode of the channel: before tBHP the channel opened to four sub-conductance levels, but it opened to only one level after tBHP. These effects by tBHP were different from the previous finding using hydrogen peroxide (H2O2), which may be explained by different oxidation patterns between the two oxidants.
Animal ; Calcium Channels/drug effects* ; Dogs ; Hydrogen Peroxide/pharmacology ; Peroxides/pharmacology* ; Sarcoplasmic Reticulum/metabolism ; Sarcoplasmic Reticulum/drug effects* ; tert-Butylhydroperoxide

It has been shown that mitochondria not only control their own Ca(2+) concentration ([Ca(2+)]), but also exert an influence over Ca(2+) signaling of the entire cell, including the endoplasmic reticulum or the sarcoplasmic reticulum, the plasma membrane, and the nucleus. That is to say, mitochondria couple cellular metabolic state with Ca(2+) transport processes. This review focuses on the ways in which the mitochondrial Ca(2+) handling system provides integrity and modulation for the cell to cope with the complex actions throughout its life cycle, enumerates some indeterminate aspects about it, and finally, prospects directions of future research.
Biological Transport ; Calcium Signaling ; Cell Membrane ; physiology ; Endoplasmic Reticulum ; physiology ; Mitochondria ; physiology ; Sarcoplasmic Reticulum ; physiology

Ischemia-reperfusion injury (IRI) has been recognized as a serious problem for therapy of cardiovascular diseases. Calcium regulation appears to be an important issue in the study of IRI. This article reviews calcium regulation in myocardial and vascular IRI, including the calcium overload and calcium sensitivity in IRI. This review is focused on the key players in Ca(2+) handling in IRI, including membrane damage resulting in increase in Ca(2+) influx, reverse-mode of Na(+)-Ca(2+) exchangers leading to increased Ca(2+) entry, the decreased activity of sarcoplasmic reticulum (SR) Ca(2+)-ATPase causing SR Ca(2+) uptake dysfunction, and increased activity of Rho kinase. These key players in Ca(2+) homeostasis will provide promising strategies and potential targets for therapy of cardiovascular IRI.
Animals ; Calcium ; metabolism ; Heart ; physiopathology ; Homeostasis ; Humans ; Myocardial Reperfusion Injury ; metabolism ; Myocardium ; Sarcoplasmic Reticulum ; metabolism ; Sarcoplasmic Reticulum Calcium-Transporting ATPases ; metabolism ; Sodium-Calcium Exchanger ; metabolism

The purpose of the present study was to investigate whether interleukin-2 (IL-2) changes the activity of sarcoplasmic reticulum (SR) Ca(2+) ATPase, sarcolemmal Ca(2+)ATPase and Na(+)/K(+) ATPase by measuring the Pi liberated from ATP hydrolysis with colorimetrical methods. It was shown that the activity of Ca(2+)ATPase in SR from IL-2-perfused (10, 40, 200, 800 U/ml) rat heart increased dose-dependently. After incubation of the SR with ATP (0.1 approximately 4 mmol/L), the activity of SR Ca(2+)ATPase increased dose-dependently in the control group. In the SR from 200 U/ml IL-2-perfused hearts, the activity of Ca(2+)ATPase was much higher than that in the control group. On the other hand, incubation of the SR with Ca(2+) (1 approximately 40 micromol/L) increased the activity of SR Ca(2+) ATPase in the control group. The activity of SR Ca(2+)ATPase of IL-2-perfused hearts was inhibited as the function to Ca(2+). Pretreatment with specific kappa-opioid receptor antagonist nor-BNI (10 nmol/L) for 5 min attenuated the effect of IL-2 (200 U/ml) on the activity of SR Ca(2+) ATPase. After pretreatment with pertussis toxin (PTX, 5 mg/L) or U73122 (5 micromol/L), IL-2 failed to increase SR Ca(2+)ATPase activity. The activity of SR Ca(2+)ATPase was not changed by incubation of SR isolated from normal hearts with IL-2. Perfusion of rat heart with IL-2 did not affect the activity of sarcolemmal Ca(2+)ATPase and Na(+)/K(+)ATPase. It is concluded that perfusion of rat heart with IL-2 increases the activity of SR Ca(2+)ATPase dose-dependently, which is mainly mediated by cardiac kappa-opioid receptor pathway including a PTX sensitive Gi-protein and phospholipase C. IL-2 increases the activity of SR Ca(2+)ATPase as the function to ATP, but inhibits the activity of SR Ca(2+)ATPase as the function to Ca(2+). IL-2 has no effect on the activity of sarcolemmal Ca(2+)ATPase and Na(+)/K(+)ATPase.
Animals ; Interleukin-2 ; pharmacology ; Male ; Myocardium ; enzymology ; Rats ; Rats, Sprague-Dawley ; Sarcolemma ; enzymology ; Sarcoplasmic Reticulum ; enzymology ; Sarcoplasmic Reticulum Calcium-Transporting ATPases ; metabolism ; Sodium-Potassium-Exchanging ATPase ; metabolism