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M T Crow

Publications and source records attributed to M T Crow.

15 recordsLinked to original sources
PubMed1995

Age-associated increase in rat ventricular ANP gene expression correlates with cardiac hypertrophy.

Atrial natriuretic peptide (ANP), a cardiac-specific hormone, is stored in the atria and released in response to atrial stretch. During cardiac hypertrophy, ANP gene expression is markedly upregulated in the left ventricle (LV). Because the hearts of normotensive senescent rats exhibit left atrial (LA) and left ventricular (LV) hypertrophy and dilatation, we examined ANP mRNA levels by Northern blot analysis and ANP peptide concentrations by radioimmunoassay in atria, LVs, and plasma of rats at 2, 6, 18, and 22-24 mo of age. Compared with LVs of 6-mo-old rats, the LV-to-body weight ratio was elevated 30% by 18 mo of age, whereas levels of ANP mRNA were elevated twofold (not significant) and sevenfold (P < 0.05) in the LV of 18- and 22- to 24-mo-old rats, respectively. The concentration of immunoreactive ANP (ir-ANP) exhibited a four- to fivefold increase in LVs of 18- and 22- to 24-mo-old rats compared with values for 6-mo-old rats (43 +/- 4 pmol/g wet wt; means +/- SE). Among 18-and 22- to 24-mo-old rats a significant correlation was observed between ANP peptide concentration and LV hypertrophy (r 2 = 0.64). Levels of ANP mRNA and ir-ANP in the atria exhibited only modest changes with aging.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Intracellular signaling pathways required for rat vascular smooth muscle cell migration. Interactions between basic fibroblast growth factor and platelet-derived growth factor.

Intracellular signaling pathways activated by both PDGF and basic fibroblast growth factor (bFGF) have been implicated in the migration of vascular smooth muscle cells (VSMC), a key step in the pathogenesis of many vascular diseases. We demonstrate here that, while bFGF is a weak chemoattractant for VSMCs, it is required for the PDGF-directed migration of VSMCs and the activation of calcium/calmodulin-dependent protein kinase II (CamKinase II), an intracellular event that we have previously shown to be important in the regulation of VSMC migration. Neutralizing antibodies to bFGF caused a dramatic reduction in the size of the intracellular calcium transient normally seen after PDGF stimulation and inhibited both PDGF-directed VSMC migration and CamKinase II activation. Partially restoring the calcium transient with ionomycin restored migration and CamKinase II activation as did the forced expression of a mutant CamKinase II that had been "locked" in the active state by site-directed mutagenesis. These results suggest that bFGF links PDGF receptor stimulation to changes in intracellular calcium and CamKinase II activation, reinforcing the central role played by CamKinase II in regulating VSMC migration.

Animals↗
PubMed1991

Phorbol esters selectively downregulate contractile protein gene expression in terminally differentiated myotubes through transcriptional repression and message destabilization.

Chronic exposure of differentiated avian skeletal muscle cells in culture to the phorbol ester, 12-O-tetradecanoyl phorbol-13-acetate (PMA), results in the selective disassembly of sarcomeric structures and loss of muscle-specific contractile proteins, leaving cytoskeletal structures and their associated proteins intact. We demonstrate here that these morphological and biochemical changes are accompanied by dramatic and selective decreases in the level of the mRNAs that encode the contractile proteins. We measured the effects of PMA on the transcriptional activity and mRNA stability of four contractile protein genes (alpha-cardiac and alpha-skeletal actin, cardiac troponin C [cTnC], and myosin light chain lf [MLClf]) and two nonmuscle genes (beta-cytoplasmic actin and the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase [GAPDH]). The transcriptional activity of the alpha-cardiac actin and cTnC genes dramatically decreased by 8 h after the addition of PMA, while other muscle and nonmuscle genes examined showed no change. Pulse-chase experiments of in vivo labeled RNA showed significant reductions in mRNA half-lifes for all the contractile protein mRNAs examined, while the half-lifes of beta-actin and GAPDH mRNA were unchanged. All of the above effects occurred under conditions in which cellular protein kinase C (PKC) levels had been reduced by greater than 90%. The fact that many of the contractile protein genes remained transcriptionally active despite the fact that the cells were unable to accumulate their mRNAs to any significant extent indicated that the treated cells were still committed to skeletal muscle differentiation. The selective changes in the stability of the contractile protein mRNAs suggest that the control of mRNA stability may be part of the normal regulatory program of skeletal muscle differentiation and that this control may be linked to the integrity of the contractile apparatus and mediated by second messenger pathways involving PKC activation.

Animals↗
PubMed1989

Fast myosin heavy chain expression during the early and late embryonic stages of chicken skeletal muscle development.

The development of embryonic skeletal muscles in the chick can be divided into two periods of fiber specialization--an early one during which the different muscles of the limb are formed and an initial round of fiber specialization occurs and a late or fetal period during which there is extensive growth of this previously established fiber pattern. This latter period of growth is dependent on the establishment and maintenance of functional neuromuscular contacts. As has been described for other developmental stages, we show here that there are different embryonic fast skeletal muscle myosin heavy chain (MHC) isoforms expressed during the different embryonic periods of muscle growth. The identification of these isoforms was based on differences in their reactivity with various fast MHC monoclonal antibodies and on their different peptide banding patterns. The in ovo accumulation of the late embryonic MHC isoform pattern was similar to the time course of the previously described changes in alpha-actin and troponin T isotype switching during embryogenesis. The appearances of the late embryonic isoforms were blocked by chronic treatment with the neuromuscular blocking agent, d-tubocurarine, and cell cultures of embryonic chicken skeletal muscle which differentiated in the absence of motorneurons expressed little of the late embryonic isoform, indicating that the expression of the late embryonic isoform was dependent on functional nerve-muscle interactions. These different embryonic fast MHC isoforms provide important markers for monitoring the progression of muscle through its embryonic stages and its interaction with motorneurons.

Animals↗
PubMed1986

The developmental program of fast myosin heavy chain expression in avian skeletal muscles.

We have examined the types of fast myosin heavy chains (MHCs) expressed in a number of different developing chicken skeletal muscles by combining peptide mapping and immunoblotting to identify fast MHC-specific peptides among the total mixture of MHC digestion products. Using this technique, we have identified three different fast MHC patterns among the different fast and mixed (i.e., fast and slow) fiber type muscles of the adult. While the different muscles all underwent sequential changes in fast MHC isoform expression during their development, the exact sequence of these changes and the isoform patterns expressed varied from muscle to muscle. During late embryonic or fetal development, all muscles expressed a similar fast MHC pattern (designated here as the fetal pattern) which was replaced shortly after hatching with a different fast MHC pattern (the neonatal pattern). During the transition from the neonatal to the adult state that occurred sometime in the first year after hatching, many of the muscles underwent additional changes in fast MHC isoform expression. In muscles such as the pectoralis major and pectoralis minor, a new fast MHC isoform pattern was seen in the adult so that the developmental program of isoform switching in these muscles involved the sequential appearance of distinct fetal, neonatal, and adult fast MHCs. Other muscles, such as the sartorius and posterior latissimus dorsi, underwent a qualitatively different program of isoform switching and expressed as an adult a fast MHC pattern that was indistinguishable from that expressed during fetal development. Finally, in some muscles, such as the superficial biceps, no change in isoform pattern was detected during the neonatal to adult transition--in these muscles, expression of the neonatal MHC isoform pattern apparently persisted into the adult state. These data indicate that no single scheme or program of fast MHC isoform switching can describe all the developmental changes that occur in fast MHC isoform expression in the chicken and that at least three different programs of isoform switching and expression can be identified.

Animals↗
PubMed1986

Myosin expression and specialization among the earliest muscle fibers of the developing avian limb.

Monoclonal antibodies specific to the light- and heavy-chain subunits of chicken skeletal muscle myosin have been used to identify fast and slow myosin-containing fibers in the thigh muscles of embryonic and adult chickens and to determine when in development diversification of muscle fiber types first occurs. Primary generation fibers which expressed different MLC and MHC types were evident within the dorsal and ventral premuscle masses and in the first muscles to form in the limb. These early embryonic muscle fiber types became distributed among and within the individual muscles of the thigh in a characteristic spatial pattern which served as a "blueprint" for guiding future muscle development and predicting the future fiber composition of the muscle. Despite the continuous addition of muscle fibers to the limb throughout development, the pattern remained unchanged. Neither the time of appearance, initial specialization, nor characteristic distribution of these primary fiber types within the limb was altered during the early embryonic period by chronic neuromuscular paralysis induced by D-tubocurarine. In contrast, muscles at later stages of embryonic development were markedly affected by such treatments and underwent atrophy and loss of differential staining characteristics. These results demonstrate that diversification of fibers in terms of myosin content is one of the earliest events in the formation of these muscles and suggest that the development of avian muscles be divided into two phases: an embryonic phase during which fibers of differing myosin content appear independently of innervation to become distributed in a specific topographic pattern within each muscle as it forms, followed by a fetal phase during which innervation becomes essential for maintaining this pattern and modulating the myosin content of its fibers.

Animals↗
PubMed1985

Slow and fast myosin heavy chain content defines three types of myotubes in early muscle cell cultures.

We prepared monoclonal antibodies specific for fast or slow classes of myosin heavy chain isoforms in the chicken and used them to probe myosin expression in cultures of myotubes derived from embryonic chicken myoblasts. Myosin heavy chain expression was assayed by gel electrophoresis and immunoblotting of extracted myosin and by immunostaining of cultures of myotubes. Myotubes that formed from embryonic day 5-6 pectoral myoblasts synthesized both a fast and a slow class of myosin heavy chain, which were electrophoretically and immunologically distinct, but only the fast class of myosin heavy chain was synthesized by myotubes that formed in cultures of embryonic day 8 or older myoblasts. Furthermore, three types of myotubes formed in cultures of embryonic day 5-6 myoblasts: one that contained only a fast myosin heavy chain, a second that contained only a slow myosin heavy chain, and a third that contained both a fast and a slow heavy chain. Myotubes that formed in cultures of embryonic day 8 or older myoblasts, however, were of a single type that synthesized only a fast class of myosin heavy chain. Regardless of whether myoblasts from embryonic day 6 pectoral muscle were cultured alone or mixed with an equal number of myoblasts from embryonic day 12 muscle, the number of myotubes that formed and contained a slow class of myosin was the same. These results demonstrate that the slow class of myosin heavy chain can be synthesized by myotubes formed in cell culture, and that three types of myotubes form in culture from pectoral muscle myoblasts that are isolated early in development, but only one type of myotube forms from older myoblasts; and they suggest that muscle fiber formation probably depends upon different populations of myoblasts that co-exist and remain distinct during myogenesis.

Animals↗
PubMed1983

Myosin light-chain expression during avian muscle development.

Monoclonal antibodies to adult chicken myosin light chains were generated and used to quantitate the types of myosin light-chain (MLC) isoforms expressed during development of the pectoralis major (PM), anterior latissimus dorsi (ALD), and medial adductor (MA) muscles of the chicken. These are muscles which, in the adult, are composed predominantly of fast, slow, and a mixture of fiber types, respectively. Three distinct phases of MLC expression characterized the development of the PM and MA muscles. The first identifiable pase occurred during the period of 5-7 d of incubation in ovo. Extracts of muscles from the pectoral region (which included the presumptive PM muscle) contained only fast MLC isoforms. This period of exclusive fast light-chain synthesis was followed by a phase (8- 12 d of incubation in ovo) in which coexpression of both fast and slow MLC isoforms was apparent in both PM and MA muscles. During the period, the composition of both fast and slow MLC isoforms in the PM and MA muscles was identical. Beginning at day 12 in ovo, the ALD was also subjected to immunochemical analyses. The proportion of fast and slow MLCs in this muscle at day 12 was similar to that present in the other muscles studied. The third development phase of MLC expression began at approximately 12 d of incubation in ovo and encompassed the transition in MLC composition to the isoform patterns incubation in ovo and encompassed the transition in MLC composition to the isoform patterns typical of adult muscle. During this period, the relative proportion of slow MLC rose in both the MA and ALD and fell in the PM. By day 16, the third fast light chain, LC(3f), was apparent in extracts of both the PM and MA. These results show that there is a developmental progression in the expression of MLC in the two avian muscles studied from day 5 in ovo; first, only fast MLCs are accumulated, then both fast and slow MLC isoforms are expressed. Only during the latter third of development in ovo is the final MLC isoform pattern characteristic of a particular muscle type expressed.

Animals↗
PubMed1983

Correlated reduction of velocity of shortening and the rate of energy utilization in mouse fast-twitch muscle during a continuous tetanus.

Isometric tetani of slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles of the mouse were studied at 20 degrees C. The total energy cost for 3- and 9-s isometric tetani was measured as a function of length above L0 and partitioned into a filament overlap-dependent fraction and a smaller filament overlap-independent fraction. In both muscles, the rate of filament overlap-independent energy cost did not change with tetanic duration. In the EDL, but not in the soleus, the rate of filament overlap-dependent energy utilization was greater in a 3-s tetanus than in a 9-s tetanus. The force-velocity relationships were studied after 3 and 9 s of isometric tetanus. In the soleus, Vmax was 2 fiber lengths/s and was not dependent on the duration of isometric tetanus. In contrast, in the EDL, Vmas decreased from 5.9 fiber lengths/s at 3 s to 3.9 fiber lengths/s at 9 s. The velocity of unloaded shortening (Vus) was examined by the slack test method as a function of the duration of isometric tetanus duration over the range of 1-15 s. In the soleus, Vus did not change, whereas in the EDL, Vus declined progressively from 6.4 to 3.2 fiber lengths/s after an isometric tetanus of increasing duration from 1 to 15 s. These results cannot exclude the hypothesis that in a maintained tetanus there is a decrease in the intrinsic cross-bridge turnover rate in the fast-twitch EDL, but not in the slow-twitch soleus muscle.

Animals↗
PubMed1982

Phosphorylation of myosin light chains in mouse fast-twitch muscle associated with reduced actomyosin turnover rate.

Phosphorylation of the 18,000-dalton light chains of the fast-twitch myosin in mouse extensor digitorum longus muscles was correlated with reduction in the rate of the actomyosin adenosinetriphosphatase in vivo, but neither of these changes occurred in the soleus muscle. These results suggest that actomyosin interactions can be down-regulated by a reversible covalent modification of myosin light chains, that a mechanism for thick-filament regulation occurs in vertebrate skeletal muscle, and that the expression of this regulation may be limited to a specific fiber type.

Actomyosin↗
PubMed1982

Myosin light chain phosphorylation is associated with a decrease in the energy cost for contraction in fast twitch mouse muscle.

The rate of splitting of energy-rich phosphate compounds and the extent of myosin light chain phosphorylation in contracting mouse extensor digitorum longus (EDL, fast twitch) and soleus (slow twitch) muscles were studied at 20 degrees C. The rate of high energy phosphate-splitting during a maintained isometric tetanus was 1.44 +/- 0.21 mumol . g-1 . s-1 in soleus. In EDL, the splitting rate was higher, 3.71 +/- 0.62 mumol . g-1 . s-1, during the first several seconds and thereafter was reduced to a rate of 1.63 +/- 0.35 mumol . g-1 . s-1 between 12 and 15 s of stimulation. Light chains identified on 2-dimensional gel electrophoretograms from EDL corresponded to the light chain composition of fast twitch muscle (LC1f, LC2f, and LC3f). Soleus is composed of fast twitch and slow twitch fibers because 2 additional light chains were found: LC1s and LC2s. In unstimulated EDL and soleus muscles, 0.1 of the LC1f and LC2s were phosphorylated. Upon stimulation, only LC2f, and only in EDL, increased its extent of phosphorylation. The time course of increase in phosphorylation of LC2f and decrease in rate of high energy phosphate-splitting correspond so that the 2 processes may be mechanistically related. If so, it appears that myosin LC2f phosphorylation represents a thick filament regulatory system capable of downward modulation of actomyosin ATPase in vivo during a maintained contraction.

Animals↗
PubMed1982

Chemical energetics of slow- and fast-twitch muscles of the mouse.

The energy utilization associated with contraction was measured in isolated slow- and fast-twitch muscles of the mouse at 20 degrees C. The extent of this utilization was estimated from either the extent of high-energy phosphate splitting occurring during contraction (the initial chemical change, delta approximately P init) or from the extent of recovery resynthesis calculated from the observed oxygen consumption and lactate production occurring during the recovery period (recovery chemical resynthesis, delta approximately P rec). For short tetani, the cost to maintain isometric tension in the fast-twitch extensor digitorum longus (EDL) was approximately threefold greater than that in the slow-twitch soleus. With prolonged stimulation, however, the energy cost in the EDL diminished so that after 12 s of stimulation, the energy cost in the EDL was only 50% greater than that of the soleus. For both the slow-twitch soleus and the fast-twitch EDL and for all tetanus durations (up to 15 s), the extent of the initial chemical change was identical with the amount of recovery chemical resynthesis, showing that a biochemical energy balance existed in these muscles.

Adenosine Triphosphate↗