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Query: UNIPROT:P06889 (Mol)
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Radiolabeled deoxyglucose (FDG) has been advocated as a marker of viability of reperfused myocardium during acute infarction. However, data for such recommendation are few. We investigated cardiac deposition of C-14 deoxyglucose (C-14 DG) and of Thallium -201 (Tl-201) in rabbits subjected to coronary occlusion (15, 30, 60 or greater than 100 min) and reperfusion (75 min and 24 h). Measured myocardial concentrations of C-14 DG and Tl-201 in macroautoradiograms were quantitatively correlated in a 24 h reperfusion group with presence of myocardial necrosis evaluated by light microscopy. The major finding in this investigation was that with 30 min or 60 min of ischemia followed by reperfusion there were myocardial regions with significant hypoperfusion (Tl-201) and histologic necrosis. However, in the same myocardial areas, the deposition of C-14 DG was not correlated with the extent of necrosis (r = 0.27). Also, the deposition of C-14 DG in acute myocardial infarction was higher than that of Tl-201 (P = 0.05 by paired T test and by nonparametric Wilcoxon's test). It was also demonstrated that when the occlusion time was varied (15-130 min) and early reperfusion was provided for 75 min or omitted altogether, the myocardial accumulation of Tl-201 was variable and that myocardial sequestration of C-14 DG was higher than perfusion in central and peripheral portions of the area-at-risk. These observations do not support a role for the use of radiolabeled deoxyglucose for the detection of myocardial viability in recently infarcted cardiac muscle.
J Mol Cell Cardiol 1991 May
PMID:Discordance between accumulation of C-14 deoxyglucose and Tl-201 in reperfused myocardium. 188 39

The effects on sarcoplasmic reticulum (SR) Ca2+ transport of solutions mimicking the important intracellular milieu changes associated with short-term hypoxia (hypoxic solutions, as described by Kammermeier et al. J. Mol. Cell. Cardiol. 14: 267, 1982) were examined. SR Ca2+ content was estimated by measuring the magnitude of the caffeine-induced contracture in saponin-skinned rat papillary muscle. SR Ca2+ uptake was inhibited by hypoxic solutions only at loading times less than or equal to 30 s. This inhibition was primarily due to the increase in Pi. The hypoxic solutions had no effect on Ca(2+)-induced Ca2+ release from the SR. We also tested the effects of ATP-free (rigor) solutions that mimic the intracellular environment during late hypoxia and ischemia. Elevating Pi or ADP alone in rigor solution had no effect on SR Ca2+ content. However, elevating Pi and ADP (+/-Mg2+) produced a 44-48% reduction in SR Ca2+ content. This reduction is most likely due to reversal of the SR Ca2+ pump. We conclude that the changes in milieu with short-term hypoxia can depress contractility in intact cardiac muscle by inhibiting SR Ca2+ uptake. During long-term hypoxia or ischemia, these milieu changes can elevate intracellular Ca2+ by reversing the SR Ca2+ pump.
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PMID:Intracellular milieu changes associated with hypoxia impair sarcoplasmic reticulum Ca2+ transport in cardiac muscle. 188 12

In a previous study we described the inhibitory action of a cytosolic protein fraction from heart muscle on ATP-dependent Ca2+ uptake by sarcoplasmic reticulum (SR); further, this inhibition was shown to be blocked by an inhibitor antagonist, also derived from the cytosol (Narayanan et al. Biochim Biophys Acta 735: 53-66, 1983). The present study investigated the ontogenetic expression of the activities of Ca2+ transport inhibitor and inhibitor antagonist in heart cytosol during fetal and postnatal development of the rat. The SR Ca2+ transport inhibitor activity was undetectable in the cytosol of fetal (15- or 20-days gestation) rat heart but was manifested in the cytosol as early as one day after birth and increased progressively thereafter to reach almost adult levels within the first two weeks of postnatal development. The activity of the SR Ca2+ transport inhibitor antagonist was barely detectable in the near-term (20 days gestation) fetus but increased substantially during early postnatal development, in parallel with the rise in activity of the inhibitor. The ontogenetic appearance and increase in the activities of the Ca2+ transport inhibitor and its antagonist correlated well with the concurrent appearance and increase in the amounts of two polypeptides of apparent molecular weights 43 kDa and 64 kDa, which we have tentatively identified as the inhibitor and inhibitor antagonist, respectively. The co-ordinated expression of both the inhibitor and inhibitor antagonist activities in the cytosol during the early postnatal period parallels the morphogenesis and functional maturation of SR in cardiac muscle suggesting likely involvement of these cytosolic proteins in the physiological regulation of SR function.
Mol Cell Biochem 1991 Jul 24
PMID:Ontogeny of cytosolic proteins capable of modulating sarcoplasmic reticulum calcium transport in heart muscle. 192 13

The voltage-dependent slow channels in the myocardial cell membrane are the major pathway by which Ca2+ ions enter the cell during excitation for initiation and regulation of the force of contraction of cardiac muscle. The slow channels have some special properties, including functional dependence on metabolic energy, selective blockade by acidosis, and regulation by the intracellular cyclic nucleotide levels. Because of these special properties of the slow channels, Ca2+ influx into the myocardial cell can be controlled by extrinsic factors (such as autonomic nerve stimulation or circulating hormones) and by intrinsic factors (such as cellular pH or ATP level). The slow Ca2+ channels of the heart are regulated by cAMP in a stimulatory fashion. Elevation of cAMP produces a very rapid increase in number of slow channels available for voltage activation during excitation. The probability of a slow channel opening and the mean open time of the channel are increased. Therefore, any agent that increases the cAMP level of the myocardial cell will tend to potentiate ISi, Ca2+ influx, and contraction. The myocardial slow Ca2+ channels are also regulated by cGMP, in a manner that is opposite to that of cAMP. The effect of cGMP is presumably mediated by means of phosphorylation of a protein, as for example, a regulatory protein (inhibitory-type) associated with the slow channel. Preliminary data suggest that calmodulin also may play a role in regulation of the myocardial slow Ca2+ channels, possibly mediated by the Ca2(+)-calmodulin-protein kinase and phosphorylation of some regulatory-type of protein. Thus, it appears that the slow Ca2+ channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of extrinsic and intrinsic factors. VSM cells contain two types of Ca2+ channels: slow (L-type) Ca2+ channels and fast (T-type) Ca2+ channels. Although regulation of voltage-dependent Ca2+ slow channels of VSM cells have not been fully clarified yet, we have made some progress towards answering this question. Slow (L-type, high-threshold) Ca2+ channels may be modified by phosphorylation of the channel protein or an associated regulatory protein. In contrast to cardiac muscle where cAMP and cGMP have antagonistic effects on Ca2+ slow channel activity, in VSM, cAMP and cGMP have similar effects, namely inhibition of the Ca2+ slow channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Cell Biochem 1990 Dec 20
PMID:Properties of calcium channels in cardiac muscle and vascular smooth muscle. 196 48

Physiological expression of the cardiac muscle myosin light-chain 2 (MLC-2) gene in chickens is restricted to cardiac muscle tissue only, at least during the late embryonic to adult stages of development. The mechanism by which cardiac MLC-2 gene expression is repressed in differentiated noncardiac muscle tissues is unknown. Using sequential 5'-deletion mutants of the cardiac MLC-2 promoter introduced into primary skeletal muscle cells in culture, we have demonstrated that a 89-bp region, designated the cardiac-specific sequence (CSS), is essential for repression of cardiac MLC-2 expression in skeletal muscle. Removal of the CSS sequence alone allows transcription in skeletal muscle cells without affecting the transcriptional activity of the promoter in cardiac muscle cells. DNase I footprinting and gel shift assays indicate that protein binding to sequences in the CSS domain occurs readily in nuclear extracts obtained from skeletal muscle but not in extracts isolated under identical conditions from cardiac muscle. Thus, it appears that a negative regulatory mechanism accounts for the lack of expression of the cardiac MLC-2 gene in skeletal muscle and that the CSS element and its binding proteins are important functional components of the regulatory apparatus which ensures the developmental program for cardiac tissue-specific gene expression.
Mol Cell Biol 1991 Mar
PMID:Tissue-specific transcription of the cardiac myosin light-chain 2 gene is regulated by an upstream repressor element. 199 16

Monoclonal and polyclonal antibodies to the major sarcoplasmic reticulum proteins of rabbit skeletal and canine cardiac muscle have been used to identify and characterize the corresponding components of human cardiac sarcoplasmic reticulum. The Ca2(+)-transporting ATPase of human cardiac sarcoplasmic reticulum was identified as a 105,000-Da protein antigenically distinct from its rabbit skeletal muscle counterpart. Human cardiac sarcoplasmic reticulum also contained 53,000- 155,000- and 165,000-Da glycoproteins antigenically related to the low and high molecular weight glycoproteins of canine cardiac and rabbit skeletal muscle sarcoplasmic reticulum. The ryanodine-sensitive Ca2+ channel of human cardiac sarcoplasmic reticulum was identified as a 400,000-Da protein antigenically related to its counterparts in canine cardiac and rabbit skeletal muscle. Human cardiac calsequestrin was identified as a 52,000-Da protein. Human phospholamban was identified as a 29,000-Da substrate for phosphorylation by cAMP-dependent protein kinase. Immunoblots of sarcoplasmic reticulum from the normal left ventricles of four unmatched organ donors and the excised failing left ventricles of nine patients with idiopathic dilated cardiomyopathy were compared in search of qualitative differences in the protein patterns of the failing hearts. No such differences were found with respect to the Ca2+ ATPase, the 53,000-Da glycoprotein, the ryanodine-sensitive Ca2+ channel, calsequestrin or phospholamban. In contrast, the 165,000-Da glycoprotein band, present in all four preparations from nonfailing hearts, was absent from three of nine preparations from failing hearts, and staining of the 155,000-Da glycoprotein in these three preparations appeared to be relatively increased. The absence of the 165,000-Da glycoprotein band may identify or reflect a pathogenetic mechanism in a subset of patients with idiopathic dilated cardiomyopathy.
J Mol Cell Cardiol 1990 Dec
PMID:Identification and characterization of proteins in sarcoplasmic reticulum from normal and failing human left ventricles. 208 60

The activity of poly (ADP-ribose) polymerase (ADPRP) and the content of 2',5'-oligodenylates core (2',5'An; n = 2,3 and 4) were measured in homogenates of the uterus and of the liver of immature rats immediately before (time 0) or at different times after injection of estradiol-valerate. ADPRP activity increased gradually, starting 6 hours after estrogen injection, for about 4 days. Instead, the content of 2',5'An decreased by about 50% within 6 hours, and thereafter more slowly for 4 days to about 20% of starting values. Estrogen increased ADPRP activity and decreased 2',5'An concentration also in the kidney and in the cardiac muscle of the same animals, but not in the skeletal muscle, where neither of the two parameters was affected. Injection of vehicle only (sesame oil) had no effect on ADPRP activity nor on 2',5'An content of immature rat tissues.
Mol Cell Biochem 1990 Dec 03
PMID:Inverse relationship between poly (ADP-ribose) polymerase activity and 2',5'-oligoadenylates core level in estrogen-treated immature rat. 212 38

The formation of human myotubes in culture is accompanied by the induction of developmentally regulated, muscle-specific genes. We have studied the expression of human myosin light chain proteins and mRNAs during myogenesis in culture, in particular the skeletal embryonic myosin light chain 1 (MC1emb), which is indistinguishable from MLC1 of adult atrial cardiac muscle (MLC1A) as has been shown for rodent and bovine MLC1emb. We have identified distinct MLC1emb/MLC1A mRNAs in cultured human skeletal muscle cells that differ in their 5' and 3' untranslated regions but contain identical protein-coding regions. The alternative 3' untranslated region is detectable also in RNA of human atria. The different MLC1emb RNAs are likely to be encoded by one gene. It appears that the two MLC1emb 5' untranslated regions of the human gene are specific for man. In the mouse, only one 5' untranslated region of the MLC1emb gene has been detected.
J Mol Biol 1990 Feb 05
PMID:Heterogenic mRNAs with an identical protein-coding region of the human embryonic myosin alkali light chain in skeletal muscle cells. 230 63

In an effort to clarify the regulation of contractions in cardiac muscle, we performed ultracentrifugation studies on the interactions between cardiac troponin and tropomyosin-actin complex in the presence of Ca2+ or Sr2+. When troponin C and troponin I were centrifuged with tropomyosin-actin complex, troponin I was not removed from tropomyosin-actin complex in the presence of bivalent-cation. Troponin C was observed to bind very weakly to troponin T-tropomyosin-actin complex in either the presence of absence of bivalent-cation. When troponin C was replaced by calmodulin, troponin I was not removed from tropomyosin-actin complex in the presence of bivalent-cation. Calmodulin bound to the troponin I-troponin T-tropomyosin-actin complex only in the presence of bivalent-cation. These results suggest that the inhibitory action of troponin I is neutralized by troponin C or calmodulin upon binding of bivalent-cation while troponin I binds to tropomyosin-actin complex in cardiac muscle. Therefore cardiac muscle seems to differ from skeletal muscle in regard to regulation of its contraction.
J Mol Cell Cardiol 1990 Mar
PMID:Ultracentrifugation study on interactions among calmodulin, cardiac troponin and tropomyosin-actin complex. 235 96

To characterize the myocardial cross-bridge dynamics in catecholamine-induced positive inotropic state, we studied the effects of adrenaline (6 X 10(-6) M) on the transient central segment length (SL) response to step decrease in tension in rat right ventricular papillary muscle in barium contracture. The time course of this response is thought to reflect the kinetics of actin-myosin interaction. The muscle was released stepwise from the steady contracture tension (Tc) to new steady tension levels (Tr) of varying magnitudes at 22 degrees C. When the tension decrease was less than 0.7 Tc, the SL transient responses comprised, in most cases, four phases. The first phase was a rapid and minute shortening during tension reduction; the second was a slow further shortening; the third, a slow lengthening; and the fourth, an extremely slow shortening toward a new steady length under the new tension. Adrenaline showed almost no effect on Tc and the amplitude of SL transients, but markedly reduced the duration of the second (D2) and third (D3) phases of SL transient regardless of the amplitude of tension reduction. The reduction of duration was 14 +/- 3% in D2 and 26 +/- 5% in D3 at Tr/Tc of 0.84 +/- 0.03 on the average (mean +/- S.D.) in nine preparations. The velocity measured from the quasi-steady SL shortening in the second phase increased with the addition of adrenaline, regardless of the amplitude of tension reduction. The increase in the shortening velocity was 16 +/- 6% (mean +/- S.D., n = 9) at Tr/Tc of 0.18 +/- 0.04. These results suggest that adrenaline increases the rate of cross-bridge cycling in cardiac muscle independent of activation level.
J Mol Cell Cardiol 1990 Apr
PMID:Adrenaline increases the rate of cross-bridge cycling in rat cardiac muscle. 238 78


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