Biomedical subjects

R L Kent

Publications and source records attributed to R L Kent.

At least 55 records · Page 3Linked to original sources

PubMed1991

Multicenter evaluation of tetracycline fiber therapy: I. Experimental design, methods, and baseline data.

The study design and baseline characteristics of a multicenter trial to test the effectiveness and safety of locally delivered tetracycline for treatment of adult periodontitis are described. Local delivery was provided by 0.5 mm diameter ethylene vinyl acetate copolymer fibers loaded 25% with tetracycline hydrochloride which were placed into periodontal pockets and maintained by an adhesive for 10 (+/- 2) days. A total of 113 subjects (56 male and 57 female; mean age 49.3 yr) at five centers participated in the study. Subjects were selected who had 4 nonadjacent teeth with 6-10 mm pockets that bled on probing. The selected sites in each subject were randomly assigned to 4 test groups: tetracycline fiber, control fiber, scaling with root planing, or untreated. A balanced experimental design was thereby established in which each subject contributed equally by providing 4 clinically comparable sites for evaluation. To provide a more specific model for testing periodontitis therapy, gingivitis was treated prior to the initiation of the study by prophylaxis with supragingival calculus removal and home care instruction. Clinical response variables measured were pocket depth reduction, attachment level gain and bleeding on controlled-force probing measured at baseline, 30 d, and 60 d. Levels of 6 bacterial species selected as probable periodontal pathogens were measured by DNA probe analysis of plaque samples. The design of this study provided several unique analytical opportunities. Controls included a comparison with conventional treatment, analysis of vehicle effects, and effects at untreated sites. Comparison of the test group with controls permitted evaluation of the principal variables that could effect interpretation of results.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Multicenter evaluation of tetracycline fiber therapy: II. Clinical response.

The safety and efficacy of periodontal disease treatment by intrapocket placement of tetracycline (TC) fibers was investigated in a 60-day multicenter study conducted by selecting 4 sites in each subject with 6-10 mm pockets that bled on probing. Sites were randomly assigned to 1 of 4 test groups: TC fiber therapy, scaling, control fiber (fibers without drug), or untreated. TC fibers and control fibers were placed to fill the pocket and were maintained with a cyanoacrylate adhesive for 10(+/- 2) d. Scaling was performed for a minimum of 5 min under local anesthesia. Following initial tooth cleaning procedures, pocket depth, attachment level and bleeding on controlled-force probing were measured at baseline and at 30 d, and 60 d following therapy. Analysis of data from 107 subjects who had complete clinical data sets indicated that TC fiber therapy significantly decreased pocket depth, increased attachment level, and decreased bleeding on controlled-force probing to a greater extent than observed in all other test groups including scaling. These effects were greater than, and in addition to, effects that occurred due to prophylaxis and improved home care. No serious adverse side-effects attributed to TC fiber therapy were observed. No TC fiber-treated sites abscessed and superinfection was not noted. A transient redness at fiber removal was seen at 21% of the sites. Although fibers were placed without anesthesia, mild pain on initial placement was infrequent (19%) and abated rapidly. The results indicate that TC fiber placement provides a safe and effective means for treatment of periodontal infections.

Adult↗

PubMed1991

CaF2 in enamel biopsies 6 weeks and 18 months after fluoride treatment.

Fluoride concentrations were studied in enamel biopsies from maxillary central incisors 6 weeks and 18 months after fluoride treatment. In the short-term study biopsies were obtained prior to and after treatment with acidic sodium or ammonium fluoride. The findings showed that large amounts of fluoride were deposited in enamel from NH4F treatment (mean concentration 84,723 ppm), indicating substantial CaF2 formation. NaF treatment resulted in mean fluoride concentrations of 7,818 ppm. In the 18-month study, biopsies from 58 placebo-treated teeth were analyzed for total fluoride (mean 1,733 ppm). Twenty-five additional biopsies from placebo-treated and 58 from NH4F-treated teeth were analyzed for KOH-soluble (CaF2) and KOH-nonsoluble (apatitic) fluoride. The mean values for total fluoride were 1,669 and 2,085 ppm in the placebo-treated and in the NH4F-treated groups, respectively. The corresponding mean values for KOH-nonsoluble fluoride were 1,467 and 1,731 ppm and for KOH-soluble fluoride 202 and 354 ppm, respectively. The increase in enamel fluoride after fluoride treatment was only marginally significant. Biopsies from the ammonium fluoride treated group were significantly more likely to have high (30 vs. 8%) and moderate (28 vs. 16%) CaF2 levels and less likely to have low levels than biopsies of placebo-treated teeth (chi-square = 8.0 with 2 d.f.; p = 0.018). It is concluded that very substantial amounts of CaF2 are present in enamel 6 weeks after treatment, and small amounts may persist in the surface enamel for as long as 18 months.

Adolescent↗

PubMed1991

Cellular versus myocardial basis for the contractile dysfunction of hypertrophied myocardium.

Contractile dysfunction has been demonstrated in many previous studies of experimental right ventricular pressure-overload hypertrophy; however, given the complex changes that occur both in the cardiac muscle cell and in the multiple components of the cardiac interstitium, it is not clear whether the contractile dysfunction observed is an intrinsic property of the cardiac muscle cell or whether it is the result of a mechanically normal cardiac muscle cell contracting within an abnormal interstitial environment. The purpose of the present study was to examine the contractile behavior of cardiac muscle cells, or cardiocytes, isolated from seven cat right ventricles that were pressure-overloaded by banding the pulmonary artery; right ventricular cardiocytes from seven sham-operated cats served as controls. Cardiocytes were obtained from these cats via standard cell isolation procedures; contractile function of the cardiocytes in response to graded viscous external loads was defined by laser diffraction. The cells were stimulated to contract at a frequency of 0.25 Hz, using 100-microA direct current pulses of alternating polarity. Hypertrophied right ventricular cardiocytes obtained from banded cats showed marked systolic contractile abnormalities in comparison with right ventricular cardiocytes from sham-operated cats. The peak velocity of sarcomere shortening for the control and hypertrophied cardiocytes in 1-cp superfusate was 3.6 +/- 0.2 and 2.1 +/- 0.1 microns/sec, respectively (p less than 0.001); the maximum extent of sarcomere shortening for the control and hypertrophied cardiocytes was 0.21 +/- 0.01 and 0.14 +/- 0.01 microns, respectively (p less than 0.001). Further, the time to peak shortening in the 1-cp superfusate was significantly longer for the hypertrophied cardiocytes (150.1 +/- 3.3 versus 160.4 +/- 3.7 msec; p less than 0.04). When the relengthening properties of the cells were examined in the 1-cp superfusate, there were significant differences between cardiocyte groups. The peak rate of sarcomere relengthening was 3.5 +/- 0.2 microns/sec in the control cardiocytes and 2.2 +/- 0.17 microns/sec in the hypertrophied cardiocytes (p less than 0.001). Similarly, the time to peak velocity of sarcomere relengthening (48.8 +/- 1.8 versus 57.9 +/- 2.9 msec) and the time to 50% maximal sarcomere relengthening (57.1 +/- 3.1 versus 67.1 +/- 3.1 msec) were both significantly prolonged for the hypertrophied cardiocytes (p less than 0.02). This study shows for the first time that the contractile defect in this model of right ventricular pressure-overload hypertrophy is intrinsic to the cardiac muscle cell itself. This finding provides a basis for further, more focused investigations designed to determine the mechanisms responsible for the contractile dysfunction observed in this form of experimental cardiac hypertrophy.

Animals↗

PubMed1991

Distribution of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis by subject age.

The possible associations between periodontitis subject age and the distribution of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis were examined using an extensive data bank of subgingival plaque specimens analyzed using DNA probes. The results suggest that A. actinomycetemcomitans is strongly related to subjects in the youngest age group (10 to 19 years) with decreasing prevalence and concentration levels in older age groups. In contrast, P. gingivalis showed a reverse relationship to subject age with highest prevalence and concentration levels in older subjects (30 years and older) compared to subjects in younger age groups. Statistical testing of these relationships were highly significant. (P less than 0.0001).

Adolescent↗

PubMed1991

The mesh diagram for analysis of facial growth.

Facial growth of twins by means of proportionate analysis of changes in the location of landmarks within a rectilinear coordinate system (mesh diagram) has been conducted, utilizing cephalometric data on 148 males and 128 females, observed annually from 8 to 16 years of age. Findings show relative consistence of the facial configuration during this 8 year time period, which includes the adolescent growth spurt. The median face in each sex shows little change in the location of soft and hard tissue landmarks, except for slight advancement of the chin as well as dorsal and caudad movement of Gonion. Nonetheless, individual variations in landmark location after 8 years of growth among the subjects studied signal the hazards of prediction within the precise framework that orthodontists seek.

Adolescent↗

PubMed1990

The effect of sucrose and fat in cookies on salivation and oral retention in humans.

Six adults were served accurately weighed portions (about 5 g) of cookies varying in sucrose and fat content. The cookies were chewed and spat out at the time the subjects were ready to swallow. Additional spittings were collected at intervals up to two, three, and four min. Chewing time decreased with increase in sucrose, or with increase in fat. The volume of saliva in each spitting was calculated from its wet and dry weights, and it was assumed either (a) that saliva produced during chewing was not carried over in the retained food, or (b) that saliva was incorporated in the retained food in the same proportion as in the first spitting. Both approaches revealed that salivary flow rates were independent of cookie formulation, with two exceptions: (1) The cookie highest in sucrose produced a significantly higher flow rate during chewing, and (2) the fat-free cookie, which was hard to chew, elicited an elevated flow rate up to two min. The total volume of saliva for the entire experimental period was similar for all formulations, except the latter. Masticatory effects, therefore, appeared to predominate over sweetness stimulation, unless sugar content was very high. The volume of saliva in the food bolus at the time of swallowing correlated with chewing time. Oral clearance of the cookies did not give straight lines when logarithms of retained material were plotted against time. Initial clearance rates appeared to diminish with increasing sucrose and fat content of the cookies. Effects of sugar and fat on all parameters may reflect changes in cookie texture and the sizes of particles produced within the mouth.

Adult↗

PubMed1989

Load induction of cardiac hypertrophy.

We have shown in surgical animal models that increased and decreased cardiac loading results in myocardial hypertrophy and atrophy, respectively. These changes, which are readily reversible upon the restoration of a normal cardiac load, occur without any requirement for neural or circulating intermediary factors. In our current studies we have focused first on an unequivocal demonstration of these same phenomena in a much simpler model consisting of isolated quiescent cardiocytes maintained in serum-free medium and second on an elucidation in isolated papillary muscles of the means by which a change in cardiac load is transduced into a change in cardiac mass. Adherent isolated adult cardiocytes held at their rest length exhibit only a very gradual loss of their differentiated features. In contrast, unloaded cardiocytes in suspension culture immediately cease nuclear RNA synthesis and rapidly come to resemble unloaded cardiac muscle--a cardiocyte cellular analog of cardiac tissue atrophy, while loaded adherent cardiocytes stretched past their rest length respond in terms of synthetic activity characteristic of growth initiation--a cardiocyte cellular analog of cardiac tissue hypertrophy. Both quiescent and contracting papillary muscles exhibit increased synthesis of cardiocyte structural proteins in direct relation to active and/or passive muscle tension. This load-dependent protein synthesis appears to require initial sodium influx through deformation-dependent sarcolemmal cation channels, in a manner analogous to the dependence of mitogen-stimulated growth initiation in a variety of other cell types on initial sodium entry, albeit by a different mechanism. Thus, load variation functions as an independent regulator of cardiac growth in the adult, and sarcolemmal deformation with consequent sodium entry may be an initial direct link between load and growth in the heart.

Amanitins↗

PubMed1989

Methodological issues relative to the quantification of root surface caries.

The purpose of this study was to assess the effect upon the quantification of root surface caries (RSC) of (1) the separation of the disease into its discrete clinical phases, (2) the confounding caused by the presence of restored abraded surfaces, and (3) the decision rule formulated for dealing with lesions and restorations which involve both crown and root. It was found that the apparent prevalence of RSC varied widely depending upon arbitrary decisions as to what stages of the disease were included in the measurement scheme. The addition of restorations (confined to the root) greatly enlarged the various disease measures, but probably also introduced some degree of error since there are several indications from the data and the clinical patterns of affected surfaces which suggest that some of the restored surfaces were formerly abraded rather than carious. The inclusion of lesions and restorations involving both root and crown produced another conspicuous increment in all disease measures, which is a cause for concern given that these components are included in some studies and ignored in others. These findings serve as the basis for several recommendations for future prevalence and incidence studies of RSC.

Adult↗

PubMed1989

Clinical profiles of individuals with and without root surface caries.

As part of a collaborative multidisciplinary investigation of root surface caries (RSC), 273 subjects (median age = 57) were clinically evaluated for coronal caries, debris, calculus, gingivitis, periodontal pocketing, recession, abrasion, as well as RSC. The entire study group was divided into three subgroups: (1) subjects whose exposed root surface were without lesions or restorations (non-diseased individuals, n = 43); (2) subjects whose exposed root surfaces had one or more lesions and may or may not have had restorations (diseased individuals, n = 110); (3) subjects with one or more restorations but no lesions, since it was not known whether these restorations were preceded by RSC or abrasion the disease status of these individuals was unclear (n = 120). A comparison of Subgroup 1 (unequivocally non-diseased) and Subgroup 2 (unequivocally diseased) revealed that subjects without RSC had more teeth, less coronal caries, less recession, less debris, less calculus, less gingivitis, and more abrasion. We infer that the common factor underlying most if not all of the subgroup differences is oral hygiene which must therefore be a major disease determinant.

Dental Calculus↗

PubMed1989

Contractile function of isolated feline cardiocytes in response to viscous loading.

The classical force-velocity relationship is a standard measure of the contractile function of isolated linear cardiac muscle, but no such simple index of contractile function exists for the isolated mammalian cardiocyte. Therefore, this study established an analogous viscosity-velocity relationship for the characterization of cardiocyte contractile function. For this purpose, force was imposed on unfettered adult feline cardiocytes as a series of defined viscous loads, which provided resistance to cardiocyte shape changes during contraction. This was done by increasing the viscosity of the Krebs superfusate (37 degrees C, pH 7.4) in graded, reproducible steps from 1 to 500 centipoise by the addition of methylcellulose. Sarcomere motion within each contracting cardiocyte was measured as movement of the diffraction pattern cast onto a photodiode array by a laser beam passing through the cell. Both the rate and extent of sarcomere shortening varied inversely with increasing viscosity, whereas neither resting sarcomere length nor osmolarity was altered. Further, increased inotropism effected by paired-pulse stimulation of cardiocytes caused an upward shift of the entire viscosity-velocity relationship. Thus the cardiocyte viscosity-velocity relationship is analogous in form to the force-velocity relationship of isolated linear cardiac muscle and provides a simple reproducible method for characterizing the contractile performance of relatively large numbers of cardiocytes isolated from a single specimen of myocardium.

Animals↗

PubMed1989

Load responsiveness of protein synthesis in adult mammalian myocardium: role of cardiac deformation linked to sodium influx.

Exposure of adult mammalian myocardium to increased hemodynamic loads augments cardiac protein synthesis, ultimately leading to hypertrophy of the affected chamber. This established relationship between loading conditions and protein synthesis was examined in terms of two questions. First, is there a basic difference between the anabolic effect of a passive load imposed on diastolic myocardium and that of an active load generated by systolic myocardium? This issue was addressed by measuring [3H]phenylalanine incorporation into muscle protein in either quiescent or contracting ferret papillary muscles, set at known isometric lengths. Myocardial protein synthesis increased in proportion to total muscle tension in each case, with an equivalent relation describing both quiescent and contracting muscles. Synthesis of two contractile proteins, actin and myosin heavy chain, were enhanced by muscle loading. Thus, a quantitative rather than qualitative difference between the anabolic effects of diastolic and systolic loading was demonstrated. Second, since increased sodium influx is an initial cellular response requisite to the growth-inducing activity of many substances, and since sodium entry through stretch-activated ion channels is stimulated by deformation of the sarcolemma, does cardiac deformation during increased loading promote sodium influx as a signal to increase anabolic activity? In either quiescent or contracting papillary muscles, the rate of 24Na+ uptake was found to increase with load. Streptomycin, a cationic blocker of the mechanotransducer ion channels, was without effect on protein synthesis in stimulated but slack muscles; however, it inhibited, in a dose-related manner, the augmented protein synthesis otherwise observed in contracting muscles developing tension. At 500 microM, streptomycin did not reduce active tension, but it did reduce the synthesis of both actin and myosin heavy chain. In a second pharmacologic approach, inotropic agents were chosen which uniformly increased muscle tension development but which had contrasting effects on sodium influx. Protein synthesis increased in the presence of Na+ influx enhancers, monensin or veratridine; however, protein synthesis decreased in the presence of amiloride, a sodium influx inhibitor. Thus, myocardial protein synthesis varied directly with sodium influx despite the positive inotropic effect observed with each of these agents. In addition, inhibition of protein synthesis by ouabain demonstrated that activation of the Na+ pump is required for the anabolic effect of load.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Load regulation of the properties of adult feline cardiocytes: growth induction by cellular deformation.

Previous studies from this laboratory have demonstrated rapid and reversible changes in cardiac structure, composition, and function in response to load alterations in vivo. The purpose of the present in vitro study was to examine directly in the isolated, quiescent adult cardiocyte the potential growth-regulating effects of load changes through the use of an extremely simple and well-defined cell culture preparation. Freshly isolated cardiocytes were plated onto a deformable, laminin-coated substrate and maintained in serum-free culture medium for 3 days. On the third day in culture, the resting length of these quiescent cardiocytes, and thus their external load, was increased by linear deformation of the substrate to which these cells were firmly adhered. Cardiocyte loading resulted in increases of approximately 10% in cell length, approximately 8% in cell surface area, and approximately 7% in sarcomere length. Three markers of increased synthetic activity were then examined: 1) [3H]uridine incorporation into nuclear RNA, 2) [3H]phenylalanine incorporation into cytoplasmic protein, and 3) [3H]thymidine incorporation into DNA. Cardiocyte loading resulted in mean increases of 186% in nuclear RNA labeling and 89% in cytoplasmic protein labeling. The finding that the increase in [3H]phenylalanine incorporation could be blocked readily by cycloheximide showed that the increase in cytoplasmic labeling in response to cardiocyte loading was not simply the result of increased amino acid transport but instead resulted from the incorporation of label into newly synthesized protein. An absence of [3H]thymidine nuclear incorporation in the loaded cardiocytes indicated that DNA synthesis was not activated in these cells. These data constitute the initial demonstration that an increase in load is at least a sufficient stimulus for the induction of increased RNA and protein synthetic activity in the adult mammalian cardiocyte. This evidence for the role of load as an independent regulator of cardiac growth in the adult suggests that hemodynamic changes may lead directly to appropriate alterations in cardiac structure and composition through the transduction of this physical stimulus into one or more biochemical signals that modulate gene expression.

Animals↗

PubMed1987

Synergistic interactions between interleukin 1, tumor necrosis factor, and lymphotoxin in bone resorption.

Cytokines with bone-resorbing activity include IL 1 beta (pI 7), IL 1 alpha (pI 5), tumor necrosis factor (TNF), and lymphotoxin (LT). Possible interaction between IL 1 beta, the major mediator with osteoclast-activating factor (OAF) activity, and other cytokines was studied. By itself, IL 1 beta was 13-fold more potent than IL 1 alpha and 1000-fold more potent than either TNF or LT in stimulating bone resorption. Suboptimal concentrations of IL 1 beta or IL 1 alpha in combination with suboptimal concentrations of TNF or LT resulted in synergistic bone-resorptive responses (1.5 to 10 times the expected responses if their effects were additive). Synergy between either form of IL 1 and TNF or LT resulted in a twofold increase in activity of IL 1, and a 100-fold increase in activity of TNF or LT. However, even with optimal synergy, IL 1 beta remained 20-fold more potent in inducing bone resorption than TNF or LT. Because IL 1 beta is considerably more potent than TNF and LT in stimulating bone resorption either alone or under synergistic conditions, it is unlikely that TNF and LT are responsible for more than a minor proportion of the total bone-resorbing activity formerly referred to as OAF.

Animals↗

PubMed1986

Control of myocardial tissue components and cardiocyte organelles in pressure-overload hypertrophy of the cat right ventricle.

Previous studies have demonstrated that there is a disproportionate increase in connective tissue in right ventricular myocardium subjected to pressure-overload hypertrophy associated with depressed cardiac contractility. While the myocardium is primarily responsive to load, the aim of the present study was to determine whether catecholamines also modulate the response of myocardial tissue components and cardiocyte organelles in pressure-overload-induced cardiac hypertrophy. Four experimental groups of cats were examined: a sham-operated control group, a group which had their pulmonary arteries banded in order to induce a pressure overload, a group which had been subjected to the same pressure overload, but in addition had beta-adrenoceptor blockade produced prior to and during the pressure overloading, and a group which had been subjected to the same pressure overload, but in addition had alpha-adrenoceptor blockade produced prior to and maintained during the pressure overloading. As in our previous study, there was a significant and equivalent degree of right ventricular hypertrophy in all experimental groups with pressure overload when assessed either as the ratio of right ventricular weight to body weight or as cardiocyte cross-sectional area. At the light microscopic level, the disproportionate increase in the volume density of myocardial connective tissue seen in banded animals was completely prevented by either alpha- or beta-adrenoceptor blockade. At the electron microscopic level, there was a reduction in the mitochondrial and myofibrillar volume fractions following beta-adrenoceptor blockade. The results of this study provide evidence for a modulatory role of catecholamines in the control of myocardial connective-tissue proliferation in pressure-overload-induced cardiac hypertrophy. There is also evidence to support the role of the adrenergic nervous system in regulating cardiocyte subcellular organelles, independent of the regulation of cardiocyte size.

Adrenergic alpha-Antagonists↗

PubMed1986

Reversibility of the structural effects of pressure overload hypertrophy of cat right ventricular myocardium.

The purpose of the present quantitative structural study was to determine whether the histological alterations seen in pressure overloaded myocardium return to normal, as in vitro contractile function does, upon removal of the pressure overload stimulus. Three experimental groups of four cats each were studied: a group with pulmonary artery banding to create a pressure overload, a group that had been subjected to an equivalent duration of pressure overload and then had that pressure overload removed, and a group of sham-operated controls. Seven to 10 weeks after each operative procedure, the right ventricular pressure was elevated only in the pulmonary artery-banded group. The right ventricle/body weight ratio was significantly increased in the pressure overloaded group only. The body weight at sacrifice, the left ventricle/body weight ratio, and the right ventricular end-diastolic pressure did not differ significantly in the three groups. The striking histological changes in the right ventricular myocardium hypertrophing in response to a pressure overload were the decrease in the volume density of cardiocytes and the increase in connective tissue in papillary muscles. These were reversed when the pressure overload was removed. This study demonstrates that when a pressure overload is removed, myocardial structure returns to normal as the function returns to normal. Given the critical importance of the proportion of cardiocytes and connective tissue components to both systolic and diastolic cardiac function, these data support the hypothesis that the abnormal proportions of these structures provide a potential morphological basis for at least some of the functional abnormalities observed in pressure overload hypertrophy of the cat right ventricle.

Animals↗

PubMed1986

Altered phospholipid metabolism in pressure-overload hypertrophied hearts.

The content and fatty acyl composition of phospholipids were examined in pressure-overload hypertrophied hearts. Cardiac hypertrophy was induced in rats by abdominal aortic constriction. Twenty-one days postconstriction the content of myocardial phosphatidylcholine (PC), sphingomyelin, and phosphatidylinositol (PI) was significantly elevated by 10, 10, and 20%, respectively. The essential fatty acid, linoleic acid, was markedly reduced in PC, phosphatidylethanolamine (PE), PI, and cardiolipin (CL) of hypertrophied hearts. The associated changes in fatty acyl composition were specific for the individual phospholipid class as evidenced by a significant elevation of palmitic acid in PC, docosahexaenoic acid in PE and oleic acid in CL. Alterations in fatty acyl composition of phospholipids were associated with no change in the composition of cardiac triglycerides, cardiac free fatty acids or serum lipids. The fatty acyl composition of phospholipids was also altered in pressure-overload hypertrophied hearts of cats, as evidenced by a reduction of linoleic acid and an elevation of arachidonic acid in total phospholipids. These findings demonstrate that changes in phospholipid metabolism occur in the pressure-overloaded mammalian heart. Such alterations may contribute to altered membrane function in the hypertrophied myocardium.

Animals↗

PubMed1986

Load regulation of the properties of adult feline cardiocytes. The role of substrate adhesion.

We have recently described rapid and reversible changes in cardiac structure, function, and composition in response to surgical load alteration in vivo. In the present study, we used a simple, well-defined in vitro experimental model system, consisting of terminally differentiated quiescent adult cat ventricular cardiocytes maintained in serum-free culture medium, to assess more definitively the role of loading conditions in regulating these same biological properties of heart muscle. Cardiocytes considered to be externally loaded were adherent throughout their length to a protein substrate, such that the tendency for the ends of the cells to retract was prevented. Cardiocytes considered to be unloaded were not adherent to a substrate and, thus, were free to assume a spherical shape. Cardiocyte structure and surface area were assessed, in initially identified cells, both by serial light microscopy and by terminal electron microscopy. Cardiocyte function was assessed in terms of the ability to exclude trypan blue, to remain quiescent with relaxed sarcomeres containing I-bands, and to shorten in response to electrical stimulation. Cardiocyte composition was first assessed by quantitative gel electrophoresis of proteins and then by microfluorimetric measurement of ribonucleic acid, protein, and deoxyribonucleic acid. In addition, cardiocyte incorporation of [3H]thymidine into deoxyribonucleic acid and [3H]uridine into ribonucleic acid were measured. Loading via substrate adhesion was found to be very effective in terms of each of these measurements in retaining the differentiated features of adult cardiocytes for up to 2 weeks in culture; unattached and thus unloaded cardiocytes quickly dedifferentiated. Conditions thought to stimulate cardiac growth, including catecholamine stimulation, were found to be ineffective. These experiments demonstrate that external load has a primary role in the maintenance of the basic differentiated properties of adult mammalian cardiocytes.

Animals↗