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PubMed1995

Muscle cell death during the development of head and neck muscles in the chick embryo.

Degenerating myofibers have been reported in the embryos and neonates of a number of birds and mammals, but neither the pervasiveness of the phenomenon nor the spatio-temporal patterns of degeneration has been examined in detail. Using transmission electron microscopy, we determined the patterns of muscle cell death in the chick biventer cervicis, a head extensor muscle. Cell death is most pronounced at incubation days 10 through 15, and occurs throughout the muscle. This is the period during which many myofiber clusters segregate into individual fibers, each with a separate basal lamina, and secondary myofibers become demarcated. Cells of largest diameter, presumably the primary myofibers, are preferentially affected. Degenerating cells exhibit a cohort of cytological features consistent with apoptosis, including the presence of dense, darkly-staining, hypercontracted myofibrils, misshapen nuclei with irregular chromatin condensations along the nuclear envelope, and scores of cytoplasmic vesicles and vacuoles. In cross section some large diameter muscle cells are characterized by sparse, flocculent cytoplasm that is devoid of myofibrils and organelles. Some show disintegrating cell membranes. In longitudinal section 200-300 microns long regions of hypercontracted myofibrils alternate with areas devoid of fibrils; this arrangement suggests that the myofibrils break into segments that are in register along one part of a muscle fiber and entirely absent from the adjacent length of fiber. We have observed similar patterns of muscle cell degeneration in the complexus, splenius cervicis, depressor mandibulae, and branchiomandibularis muscles. By day 18 of incubation most signs of degeneration are absent and by hatching (day 21) the muscle fibers all appear healthy. Many of these cytological changes in embryonic head muscle cells are characteristic of programmed cell death. We hypothesize that large-scale death of myocytes is a normal part of avian myogenesis and an important mechanism for affecting the transformation from embryonic to hatching muscle patterning.

Animals↗

PubMed1981

Three dimensional arrangement of mitochondria and endoplasmic reticulum in the heart muscle fiber of the rat.

The three-dimensional arrangement of mitochondria and endoplasmic reticulum was studied in thick sections of the heart left ventricle fixed in glutaraldehyde and impregnated with the Ur-Pb-Cu technique and in thin sections of glutaraldehyde-fixed tissue post-fixed in potassium ferrocyanide-reduced osmium. Squarish flattened mitochondria, approximately the size of a sarcomere, were arranged in longitudinal columns in the clefts between the myofibrils. At the periphery of the fiber, the endoplasmic reticulum took the appearance of a subsarcolemmal network of plate-like and tubular cisternae running parallel to the cell surface. Between the myofibrils, the ER network formed longitudinally oriented repetitive units whose structure varied according to their position in relation to the A- or I- bands of the myofibrils. In front of the A-band, the endoplasmic reticulum appeared as a single layered network of anastomotic tubules compressed between the adjacent myofibrils. In front of the I-band, it formed a multilayered network the three-dimensional arrangement of which was dependent upon the presence or absence of the T-tubule. In the absence of the T-tubule, the ER cisternae were loosely anastomosed and occasionally displayed bulbous terminal swellings. In the presence of T-tubules, tubular ER cisternae were seen running parallel on both sides of the T-tubules and were continuous with sheet-like cisternae sandwiched between the distended T-tubule and adjacent extremities of longitudinally arranged mitochondria. These tubular or flattened cisternae were connected to each other by numerous bridging cisternae around the T-tubules.

Animals↗

PubMed1994

Quantitative study on the relation between structural and functional properties of the hearts from three different mammals.

The ultrastructural quantitative composition of left ventricular cardiac myocytes from isolated Langendorff-perfused hearts was studied in three different mammals (rabbit, guinea pig, and rat). Volume densities of mitochondria, myofibrils, and unspecified cytoplasm were determined using morphometry and were compared to functional parameters including left ventricular developed pressure (LVDP), contractility (dP/dt), heart rate, TTI (tension-time index, an index of oxygen consumption), and relative heart mass (H/B) obtained from these hearts. Each of the mammals was found to possess a very specific and characteristic quantitative composition of cardiac myocyte. Cardiac myocytes contained 26.8% mitochondria and 56.3% myofibrils in rabbits, 25.8% mitochondria and 60.9% myofibrils in guinea pigs, and 27.7% mitochondria and 58.1% myofibrils in rats. The LVDP, contractility, heart rate, and TTI were quite different among species. However, there were close correlations between the mitochondrial volume density and the LVDP (p < 0.05), and between the mitochondrial volume density and the TTI (p < 0.05), in any group of the animals. It is concluded that the mitochondrial volume density is a good indirect indicator of function of cardiac muscle related to oxidative capacity.

Animals↗

PubMed2002

In vitro generation of differentiated cardiac myofibers on micropatterned laminin surfaces.

Cardiac muscle fibers consist of highly aligned cardiomyocytes containing myofibrils oriented parallel to the fiber axis, and successive cardiomyocytes are interconnected at their ends through specialized junctional complexes (intercalated disks). Cell culture studies of cardiac myofibrils and intercalated disks are complicated by the fact that cardiomyocytes become extremely flattened and exhibit disorganized myofibrils and diffuse intercellular junctions with neighboring cells. In this study we sought to direct the organization of cultured cardiomyocytes to more closely resemble that found in vivo. Lanes of laminin 5-50 microm wide were microcontact-printed onto nonadhesive (BSA-coated) surfaces. Adherent cardiomyocytes responded to the spatial constraints by forming elongated, rod-shaped cells whose myofibrils aligned parallel to the laminin lanes. Patterned cardiomyocytes displayed a striking, bipolar localization of the junction molecules N-cadherin and connexin43 that ultrastructurally resembled intercalated disks. When laminin lanes were widely spaced, each lane of cardiomyocytes beat independently, but with narrow-spacing cells bridged between lanes, yielding aligned fields of synchronously beating cardiomyocytes. Similar cardiomyocyte patterns were achieved on the biodegradable polymer PLGA, suggesting that patterned cardiomyocytes could be used in myocardial tissue engineering. Such highly patterned cultures could be used in cell biology and physiology studies, which require accurate reproduction of native myocardial architecture.

Animals↗

PubMed1992

Modifications in myotendinous junction structure following denervation.

Changes in the structure of myotendinous junctions in response to peripheral nerve lesions are examined by transmission electron microscopy and morphometric analysis. Modifications in the folding of the plasma membrane at myotendinous junctions relative to the cross-sectional area of myofibrils terminating at the membrane are evaluated quantitatively using a morphometric analysis in which the muscle cell processes at the myotendinous junction are modeled as circular paraboloids. Denervated frog semitendinosus muscles were analyzed at 2, 4 and 8 weeks following denervation and compared to innervated, contralateral controls. No significant differences were found in relative folding of junctional plasma membranes between any two data sets, although myofibril diameter decreased over time following denervation. This shows that junctional plasma membrane and associated junctional structures, such as basement membrane, are removed from the myotendinous junction at a rate similar to that of myofibril thinning, thereby keeping constant the ratio between junction area and myofibril cross-sectional area. Electron microscopic observations indicate that 4 weeks post-denervation is the most active stage of junction remodeling of the time points sampled.

Animals↗

PubMed1978

The action of caffeine in promoting ultrastructural damage in frog skeletal muscle fibres. Evidence for the involvement of the calcium-induced release of calcium from the sarcoplasmic reticulum.

1. Caffeine at concentrations above 5 mM was shown to cause rapidly extensive ultrastructural damage to the myofibrils of frog skeletal muscle. 2. The effect was promoted at lower temperatures, whereas the myofibrils were protected by prior exposure to procaine. 3. It is argued that caffeine causes a Ca2+-induced release of Ca2+ (the CROC) from the S.R. and that the consequent rise in [Ca2+]i promotes the ultrastructural damage observed. 4. Myofibril digradation is also produced by treatment of the muscle with the divalent cation ionophore A23187; this effect is not protected by either procaine or Dantrolene sodium. 5. It is suggested that A23187 causes the release of Ca2+ from the S.R. by a mechanism that differs from both excitation and the CROC; the resultant rise in [Ca2+]i again causes myofibril degradation. 6. The ways in which a marked rise in [Ca2+]i could cause muscle damage and the possible relevance of these findings to the sequence of events in the development of myopathies of human skeletal muscle are discussed.

Animals↗

PubMed1980

Double-immunofluorescent staining of isolated smooth muscle cells. I. preparation of anti-chicken gizzard alpha-actinin and its use with anti-chicken gizzard myosin for co-localization of alpha-actinin and myosin in chicken gizzard cells.

Contractile proteins have been co-localized by double-immunofluorescent staining in several types of cultured cells. Since freshly isolated smooth muscle cells are more representative of the organization within smooth muscle cells in the intact tissue than cultured cells, the present study was undertaken to determine the feasibility of using double-staining techniques in freshly isolated cells. A new method of purifying alpha-actinin from chicken gizzards was used to provide antigen for raising anti-alpha-actinin. Fluorescein isothiocyanate-labelled anti-alpha-actinin (FAalphaA) was used in conjunction with tetramethyl rhodamine isothiocyanate-labelled anti-myosin (TRAM) Ouchterlongy gels against myosin, tropomyosin, actin, and alpha-actinin showed that antimyosin reacted only with myosin, anti-alpha-actinin only with alpha-actinin. Anti-alpha-actinin stained only the Z-line of isolated chicken skeletal muscle myofibrils. FAalphaA stained bright, discrete patches or strips on the plasma membrane, while TRAM was excluded from these areas. FAalphaA stained myofibrils faintly in a striated pattern, while TRAM stained myofibrils heavily with less evident striations. Evidence for extramyofibrillar localization of alpha-actinin within the cytoplasm was inconclusive. Although antibodies were quite specific in their labelling, resolution with double-staining was subject to the same limitations described for single labelling of whole cells (Bagby and Pepe 1978). Double-staining of whole cells is just as feasible as single-staining. Indeed, having a definite marker for myofibrils (TRAM) makes the localization of alpha-actinin much easier to interpret.

Actinin↗

PubMed1985

Inhibition of tension development and actomyosin ATPase activity in barnacle muscle by the Ca2+-indicator dye antipyrylazo III.

We have investigated the effects of the Ca2+-indicator dye antipyrylazo III on: (1) tension development in myofibrillar preparations from barnacle depressor muscle; and (2) actomyosin ATPase activity in myofibrils/native actomyosin isolated from barnacle muscle and in actomyosin hybrids prepared from pure (unregulated) rabbit F-actin and purified barnacle myosin. In all solutions, pCa was either heavily buffered with suitable [CaEGTA]/[EGTA] and/or measured with a calcium-electrode so as to offset the appreciable Ca2+-buffering effects of the dyes. Antipyrylazo III produced a rapid, reversible and concentration-dependent inhibition of: (1) tension development by isolated barnacle myofibrils; (2) calcium-regulated ATPase activity in barnacle myofibrils and native actomyosin; and (3) calcium-independent actin-activated ATPase activity in hybrid actomyosins prepared from purified barnacle myosin and rabbit actin. This latter observation indicated that the inhibitory effect of the dye on calcium-regulated tension and ATPase in intact myofibrils is due to specific repression of active crossbridge formation rather than modification of calcium-regulatory mechanisms. The hypothesis that antipyrylazo III specifically represses active crossbridge formation was supported by the observation that the dye had no effect on rigor tension development. Specific and saturable binding of the dye to these myofibrils was characterized by a maximum capacity of 1.3 mumol dye g-1 myofibrillar protein, consistent with a calculated 1 dye: 1 myosin stoichiometry. These various biological effects were observed with both commercially available antipyrylazo III and highly purified dye preparations. Preliminary studies using myofibrillar preparations from rabbit psoas muscle, guinea-pig portal vein smooth muscle, and scallop adductor muscle have indicated that contractile function in these muscle types does not appear to be inhibited by antipyrylazo III.

Actins↗

PubMed1992

Spatial relationship of nebulin relative to other myofibrillar proteins during myogenesis in embryonic chick skeletal muscle cells in vitro.

The developmental expression of nebulin was studied in embryonic chick skeletal muscle cells in vitro by means of immunofluorescence microscopy. Initially nebulin appeared homogeneously or in a punctate form in the cytoplasm, and then it was assembled into I-Z-I-like complexes containing actin and alpha-actinin but not myosin and connectin (titin). Striated patterns of nebulin ('singlets') in myofibrils appeared simultaneously with those of alpha-actinin (Z-bands), myosin (A-bands) and connectin ('doublets'), but earlier than those of actin. After actin striations were formed as myofibrils matured, each nebulin band started to exhibit 'droplets'. The delayed development of nebulin compared to the I-Z-I brush formation and the myofibril maturation seems to indicate that this giant myofibrillar protein is unnecessary for both the initial (formation of I-Z-I-like structures) and the subsequent (regular alignment of myofibrils) phases of myofibrillogenesis.

Animals↗

PubMed1991

Cell-free incorporation of newly synthesized myosin subunits into thick myofilaments.

Although a substantial literature exists on the in vitro polymerization of purified myosin, little is known about native thick filament assembly, remodeling or turnover. We have recently described a cell-free system (Bouche et al., 1988) to examine the interactions between thick filaments and soluble, newly synthesized myofibrillar proteins. In the present manuscript we describe our studies on myosin heavy (MHC) and light chain (LC) incorporation into myofibrils or native and synthetic thick filaments. 35S-labeled myofibrillar proteins or myosin subunits were synthesized in a reticulocyte lysate translation system after which myofibrils or myofilaments were added and incubated with these proteins in the lysate. The added filaments were then sedimented and analyzed by SDS-PAGE and fluorography to establish which of the labeled protein subunits were co-pelleted. Operationally, this co-sedimentation of labeled proteins with myofilaments has been termed 'protein incorporation'. We observed that newly synthesized MHC, LCs 1, 2 and 3 all incorporated into the thick filaments. However, the quantity and specificity of LC incorporation depended upon the structure or composition of the filaments. LCs 1 and 3 were preferentially incorporated into myofibrils and native thick filaments, whereas LC2 was selectively taken up by synthetic filaments prepared from purified myosin. These results suggest that soluble MHCs and LCs interact independently with myofilaments. This hypothesis is supported by the observation that selective removal of soluble MHCs, or of a single LC, did not alter the incorporation of the remaining myosin subunits. Similarly, MHCs synthesized in the absence of LCs also incorporated into myofilaments or myofibrils. We propose that myosin subunits are capable of independent incorporation into and exchange from myofilaments.

Actin Cytoskeleton↗

PubMed1998

Cardiac hypertrophy in copper-deficient rats is owing to increased mitochondria.

Dietary copper depletion results in cardiac hypertrophy and ultrastructural alterations. The objective of this study was to determine the components that contribute to cardiac enlargement. Two groups (n = 4) of male, weaning, Sprague-Dawley rats were fed ad libitum with copper-adequate or copper-deficient diets for five weeks. Cross sectional transmission electron micrographs from both groups were evaluated using image analysis to quantify absolute area occupied by myocyte, mitochondria, myofibril, and other intracellular material. Copper-deficient rats had larger myocytes, increased area of mitochondria, and increased ratio of mitochondria:myofibril as well as mitochondria:myocyte. Copper deficiency did not change the absolute area occupied by myofibrils. These data suggested that increase in the absolute mitochondria area is the major contributory factor to the cardiac hypertrophy in copper deficiency. Under the conditions used, myofibril has minimal role toward contributing to the hypertrophic state. The pathology reported resembles human forms of genetic mitochondrial cardiomyopathies. The copper-deficient rat may be a useful model to investigate the underlying biochemical or molecular responses when peptides of enzymes are deleted.

Animals↗

PubMed1994

Histomorphometric features predict 1-year outcome of patients with idiopathic dilated cardiomyopathy considered to be at low priority for cardiac transplantation.

Cardiac transplantation for patients with idiopathic dilated cardiomyopathy (IDC) and poor left ventricular function usually is postponed until symptoms have become intolerable. However, the short-term prognosis of this subset of patients has been defined poorly. Accordingly, the 1-year outcome was investigated in 30 patients with IDC with an ejection fraction < or = 25% who showed a stabilized clinical condition at assessment for transplantation and were therefore considered at low priority for surgery. During follow-up, 10 patients (group A) showed a poor outcome: 2 died suddenly, and 8 had hemodynamic failure (4 of whom underwent transplantation and 4 of whom died from heart failure while on the waiting list). The remaining 20 patients (group B) had a benign outcome. At assessment for cardiac transplantation, clinical and electrocardiographic features, left ventricular dimension, and ejection fraction were similar between the two groups. However, group A patients had higher left ventricular end-diastolic pressure (p < 0.03) and lower cardiac index (p < 0.02) and stroke volume index (p < 0.03) with respect to group B patients. In addition, the former had a lower myofibril volume fraction (p < 0.001) and a higher nuclear area (p < 0.001) compared with the latter. Multivariate analysis selected myofibril volume fraction (p < 0.001) and nuclear area (p < 0.005) as the only independent predictors of a poor 1-year outcome. The combination of myofibril volume fraction < or = 89% and nuclear area > 50 microns 2 was found in all group A patients (sensitivity 100%) but in only 2 group B patients (specificity 90%). It is concluded that in patients with IDC considered at low priority for cardiac transplantation: (1) the 1-year freedom from a cardiac event is lower than that currently expected with surgery; (2) histomorphometric features, that is, the concurrency of low myofibril volume fraction and increased nuclear area, predict short-term outcome; and (3) endomyocardial biopsy at assessment for cardiac transplantation might improve the rationalization of the timing of the procedure.

Adult↗

PubMed1981

Adult mammalian cardiac muscle cells in culture.

Adult rat cardiac muscle cells were isolated from the ventricle by a retrograde perfusion technique through the aorta (Nag and Zak, 1979). These single, isolated cardiac muscle cells were cultured for 4 weeks. Throughout the culture period, a small number of muscle cells retained their cylindrical shape, while the rest exhibited alterations in shape and size assuming a flattened body of irregular shape with pseudopodia-like processes and thereby resembling embryonic/neonatal cardiac muscle cells in culture. Transmission electron microscopy revealed that the cylindrical muscle cells contained compactly arranged myofibrils and cellular organelles, similar to those of freshly isolated and in vivo cells. A few irregularly shaped cardiac muscle cells were similar to the cylindrical cells in their internal structural organization. Most of the irregular cells exhibited less myofibrillar content than that of the freshly dissociated and in vivo cells. Myofibrils in the irregular cells were widely spaced and myofilament of some of the myofibrils were loosely bunched. In addition, scattered patches of myofibrils and free myofilaments were observed in many of these cells. The internal structural organization of these irregularly shaped cardiac muscle cells closely resembled the embryonic and neonatal cardiac muscle cells in vitro and in vivo. Most of the muscle cells in culture continued to contract spontaneously, and electron microscope studies clearly indicated that they underwent dedifferentiation. Autoradiography studies demonstrated that the cylindrical and irregularly shaped cardiac muscle cells underwent DNA synthesis and cell division in culture.

Animals↗

PubMed1990

Role of phosphocreatine in energy transport in skeletal muscle of bullfrog studied by 31P-NMR.

To evaluate the energy-shuttle hypothesis of the phosphocreatine/creatine kinase system, diffusion rates for ATP, phosphocreatine and flux through the creatine kinase reaction were determined by 31P-NMR in resting bullfrog biceps muscle. The diffusion coefficient of phosphocreatine measured by 31P-pulsed gradient NMR was 1.4-times larger than ATP in the muscle, indicating the advantage of phosphocreatine molecules for the intracellular energy transport. The flux of the creatine kinase reaction measured by 31P-saturation transfer NMR was 3.6 mmol/kg wet wt. per s in the resting muscle. The flux is equal to the turnover rate of ATP, ADP, phosphocreatine and creatine molecules, therefore, the life-times of these substrates and the average distance traversed after the life-times by the diffusing molecules were calculated using the diffusion coefficients obtained by 31P-NMR. The mean square length of one-dimensional diffusion was 22 microns in ATP molecules and the minimum diffusion length was 1.8 microns in ADP molecules. The latter was calculated using free ADP concentration, 30 mumol/kg wet wt., obtained from the equilibrium constant of the creatine kinase reaction and the diffusion coefficient assumed to be the same of ATP in muscle. Similar diffusion lengths of ADP were calculated using the reported values for the flux of the creatine kinase reaction in heart and smooth-muscle. The diffusion lengths of all substrates involved in the creatine kinase reaction were larger than the radii of myofibrils. Therefore, in the muscles with an alternating arrangement of mitochondria and myofibrils, such as heart and certain skeletal muscles, ATP and ADP molecules can move freely between myofibrils and mitochondria without the aid of the creatine kinase reaction; thus, we conclude that the energy-shuttle hypothesis is not obligatory for energy transport between the mitochondria and the myofibrils.

Adenosine Triphosphate↗

PubMed1985

The cellular basis of the length-tension relation in cardiac muscle.

The relation between muscle length or sarcomere length and developed tension for lengths up to the optimal for contraction (Lmax) is much steeper in cardiac muscle than in skeletal muscle. The steepness of the cardiac length--tension relation arises because the degree of activation of the cardiac myofibrils by calcium increases as muscle length is increased. Two processes contribute to this length-dependence of activation: (i) the calcium sensitivity of the myofibrils increases with muscle length and (ii) the amount of calcium supplied to the myofibrils during systole increases with muscle length. Of these two, the change in calcium sensitivity is the most clearly defined and is responsible for a large part of the rapid change in developed tension when muscle length is altered. It is likely that this change in calcium sensitivity is due to a change in the affinity of troponin for calcium but the underlying mechanism has not been identified. There is good evidence that changes in the calcium supply to the myofibrils can account for the slow changes in tension that follow an alteration in length; there may also be rapid changes in calcium supply but this is less clearly established at present.

Actin Cytoskeleton↗

PubMed1985

Subcellular localization of bovine heart calcium-dependent protease inhibitor.

Four monoclonal antibodies for a calcium-dependent protease inhibitor protein were produced by fusing Sp2/0 myeloma cells with spleen cells from a Balb/C mouse immunized with purified bovine heart inhibitor. Each of the monoclonal antibodies was highly specific for the inhibitory protein as revealed by electro-blot analysis. The antibodies recognized different antigenic sites on CNBr peptides prepared from the purified inhibitor protein. Immunofluorescent microscopy of sections from bovine heart ventricles treated with each of the antibodies demonstrated the same fluorescent pattern. Fluorescence was observed at or near the sarcolemma of the myocytes, and along the Z-discs of relaxed myofibrils within the myocytes. Contracted myofibrils did not appear to bind antibody. Immunostaining of glycerinated relaxed cardiac myofibrils revealed staining at the Z-discs. One of the antibodies could also stain the Z-disc region of bovine skeletal muscle myofibrils.

Animals↗

PubMed2001

Effect of pH on the rheological and structural properties of gels of water-washed chicken-breast muscle at physiological ionic strength.

Adjustment of pH from 6.4 to neutrality improved gelling ability and water-holding capacity of twice water-washed, minced chicken-breast muscle significantly at physiological ionic strength, at which the majority of the myofibrillar proteins, including myosin, are not soluble. A strain value of 2.2 was obtained at neutral pH. Myofibrils were the main components of the gel network at both pH 6.4 and 7.0; however, the myofibrillar distribution varied with the pH value. At pH 6.4, myofibrils formed a network of localized aggregates leaving large voids between, whereas at neutral pH, an evenly distributed network of myofibrils was formed. In addition, at neutral pH, a network of fine strands was found within the network of myofibrils. The network was much less developed at pH 6.4. The thin and thick filaments within each myofibrillar structure were disorganized at both pH values. The intramyofibrillar spaces were larger at neutral pH than at pH 6.4. It was proposed that adjustment of pH to neutrality increased electrostatic repulsion leading to a more even distribution of the myofibrillar proteins, a key factor responsible for the improved gel strength and water-holding capacity.

Animals↗

PubMed1996

Covalent binding of peptides to the N-terminal hydrophobic region of cardiac troponin C has limited effects on function.

Exposure of an N-terminal hydrophobic region in troponin C is thought to be important for the regulation of contraction in striated muscle. To test this hypothesis, single Cys residues were engineered at positions 45, 81, 84, or 85 in the N-terminal hydrophobic region of cardiac troponin C (cTnC) to provide specific sites for attachment of blocking groups. A synthetic peptide, Ac-Val-Arg-Ala-Ile-Gly-Lys-Leu-Ser-Ser, or biotin was coupled to these Cys residues, and the covalent adducts were tested for activity in TnC-extracted myofibrils. Covalent modification of cTnC(C45) had no effect on maximal myofibril ATPase activity. Greatly decreased myofibril ATPase activity (70-80% inhibited) resulted when the peptide was conjugated to Cys-81 in cTnC(C81), while a lesser degree of inhibition (10-25% inhibited) resulted from covalent modification of cTnC(C84) and cTnC(C85). Inhibition was not due to an altered affinity of the cTnC(C81)/peptide conjugate for the myofibrils, and the Ca2+ dependence of ATPase activity was essentially identical to the unmodified protein. Thus, a subregion of the N-terminal hydrophobic region in cTnC is sensitive to disruption, while other regions are less important or can adapt to rather bulky blocking groups. The data suggest that Ca(2+)-sensitizing drugs may bind to the N-terminal hydrophobic region on cTnC but not interfere with transmission of the Ca2+ signal.

Amino Acid Sequence↗