Concanavalin A increases spontaneous beat rate of embryonic chick heart cell aggregates

Differential Lectin Binding Patterns Identify Distinct Heart Regions in Giant Danio ( Devario aequipinnatus) and Zebrafish ( Danio rerio) Hearts

Lectins are carbohydrate-binding proteins commonly used as biochemical and histochemical tools to study glycoconjugate (glycoproteins, glycolipids) expression patterns in cells, tissues, including mammalian hearts. However, lectins have received little attention in zebrafish ( Danio rerio) and giant danio ( Devario aequipinnatus) heart studies. Here, we sought to determine the binding patterns of six commonly used lectins-wheat germ agglutinin (WGA), Ulex europaeus agglutinin, Bandeiraea simplicifolia lectin (BS lectin), concanavalin A (Con A), Ricinus communis agglutinin I (RCA I), and Lycopersicon esculentum agglutinin (tomato lectin)-in these hearts. Con A showed broad staining in the myocardium. WGA stained cardiac myocyte borders, with binding markedly stronger in the compact heart and bulbus. BS lectin, which stained giant danio coronaries, was used to measure vascular reconstruction during regeneration. However, BS lectin reacted poorly in zebrafish. RCA I stained the compact heart of both fish. Tomato lectin stained the giant danio, and while low reactivity was seen in the zebrafish ventricle, staining was observed in their transitional cardiac myocytes. In addition, we observed unique staining patterns in the developing zebrafish heart. Lectins' ability to reveal differential glycoconjugate expression in giant danio and zebrafish hearts suggests they can serve as simple but important tools in studies of developing, adult, and regenerating fish hearts.

A new model for the research into rhythmic contraction activity of cardiomyocytes in vitro

Heart cells continue to contract rhythmically after isolation and in culture in vitro. We describe a model of heart preparation in vitro that permits quantitative research on the frequency of contractions of cardiomyocytes. The chick embryo heart explants placed on a network of elastic glass fibers continued beating for months, recorded and analyzed with the methods of computer-assisted image analysis. The efficacy of this experimental model for the screening of effects of various agents on the frequency of contractions was examined by following the effects of nifedipine, caffeine, ethanol, and benzamide. The reversibility of the effects and the reproducibility of results were demonstrated quantitatively. The significance of a mechanical elastic load provided by glass fibers for the preservation of long-lasting contractile activity of cardiomyocytes is discussed and the common occurrence of oscillatory contraction processes in various eucaryotic cells is noted.

Time-resolved confocal analysis of antibody penetration into living, solid tumor spheroids

The in vivo function of a biologically active molecule is governed in part by the dynamics of its distribution within its target tissue. To enhance our ability to probe living cells, we have endeavored to improve live confocal microscopy methods and to develop analytical methods that simplify the handling of the resulting complex data sets. To do this we attached a recently developed micro-incubation system to the stage of a Leica confocal laser scanning microscope and were able to maintain physiologic culture conditions over several hours. Axial stability was achieved by modifying the room air conditioning. Laser illumination was low enough to retain cell viability through several hours of continuous scanning. With this setup, planar, time-resolved data sets (xyt) were produced by continuously rescanning a single xy plane at the rate of one scan/min. As an alternative, volumetric data sets (xyz) were acquired by stepping the scanned plane through the z axis. In both types of data sets, a semi-quantitative determination of the concentration of a fluorescent reporter molecule (e.g., FITC) over a gray level range of 0.255 was recorded along with the positional information. Thus, concentration (as intensity of fluorescence, or i) gave a fourth variable by either scan method, resulting in high-density xyti or xyzi data sets. The biological model we used to examine these methods was the penetration of a FITC-labeled, anti-carcinoma monoclonal antibody into cultured spheroids of tumor cells bearing the antibody-binding epitope. In one case, the distribution of antibody-FITC conjugate was compared with that of a long wavelength membrane dye, DiIC18(5). Several different software analyses were compared, including examining xyt data sets as "volumes". We observed that by increasing the displayed resolution of one variable, the demonstrable resolution of the other variables was reduced. For example, with high temporal resolution, either quantitative or positional resolution had to be sacrificed. Thus, we needed to perform several different analyses of a single data set to compare all of the variables properly. In these experiments, the dynamic aspects of the changes in antibody-FITC distribution were examined. Along with comparison of antibody-FITC penetration with that of DiI, these data suggest an as yet unexplained biological transport of antibody into a tumor spheroid, which is not consistent with mere passive diffusion through the fluid of extracellular clefts. Using this model system, we have performed and analyzed highly time-resolved confocal microscopy on living specimens maintained under physiologic conditions.

Effect of dynorphin A(1?13) on cardiomyocytes in culture: modulation of the response to increased extracellular calcium, but no effect on intrinsic cardiac contractile frequency or the response to isoproterenol or increased extracellular potassium

The purpose of this study was to determine whether the endogenous opioid peptide dynorphin A(1-13) has a direct effect on the heart or acts to modulate the cardiac chronotropic response to calcium, potassium, or beta-adrenergic receptor stimulation. Spontaneously contracting myocardial cell aggregates were prepared from 7-day-old chick embryos and were maintained in culture for 72 h before study. Dynorphin A(1-13), 10(-8) to 10(-6)M, did not alter spontaneous contractile frequency. Increases in [Ca2+]o spontaneously suppressed cardiac contractile frequency, and dynorphin A(1-13) significantly (p less than 0.05) enhanced this response. Nifedipine, 10(-8) M, antagonized the effect of increased [Ca2+]o on cardiac contractile frequency, but did not block the action of dynorphin A(1-13) to accentuate the effect of increasing [Ca2+]o. Dynorphin A(1-13) did not alter the significant (p less than 0.05) increase in contractile frequency produced by beta-adrenergic receptor stimulation by isoproterenol, or the suppression in contractile frequency produced by increases in extracellular potassium ([K+]o). These data indicate that dynorphin A(1-13) does not act directly on the cardiac myocyte to alter cardiac contractile frequency or alter the response to increases in [K+]o or to isoproterenol, but that dynorphin A(1-13) does modulate the response to increases in extracellular calcium.

The effect of amiloride on the cardiac chronotropic responses to isoproterenol in myocardial aggregate cells in culture

The purpose of this study was to test the hypothesis that amiloride alters the response of cardiac myocytes to isoproterenol. Myocardial cell aggregates were prepared from 7 day-old chick embryos maintained in culture for 72 hrs before study. Isoproterenol, 10-8 M to 10-5 M, significantly (P less than 0.05) increased contractile frequency of myocardial aggregates. The effects of isoproterenol were maximum within 5 min. of exposure and declined thereafter. In the absence of isoproterenol, amiloride, at 10-6 M and 10-7 M produced a transient decrease in contractile frequency while amiloride at 10-5 M produced a significant (P less than 0.05) decrease in contractile frequency. Amiloride significantly (P less than 0.05) increased the effect of isoproterenol on cardiac contractile frequency. There was a greater and more sustained response to isoproterenol in the presence of amiloride. Furthermore, the magnitude of these effects were greater with higher concentrations of amiloride. These data indicate that amiloride accentuates the cardiac chronotropic response to isoproterenol and suggest that, because amiloride inhibits sodium entry in these cells, change in intracellular sodium may be one of the mechanisms mediating the chronotropic action of isoproterenol on the heart.

The effect of alteration of extracellular Na+ or Ca2+ and inhibition of Ca2+ entry, Na(+)-H+ exchange, and Na(+)-Ca2+ exchange by diltiazem, amiloride, and dichlorobenzamil on the response of cardiac cell aggregates to epidermal growth factor

The purpose of this study was to examine the effect of epidermal growth factor (EGF) on cardiac function and to explore ionic mechanisms as potential explanations for EGF-induced changes in cardiac contractile frequency. Cardiac cell aggregates were prepared from 7-day-old chick embryo hearts and were maintained in culture. EGF over a concentration range of 5 to 20 ng/ml produced a dose-dependent increase in cardiac contractile frequency. Inhibition of Na(+)-H+ exchange by amiloride antagonized the action of EGF. Inhibition of Na(+)-Ca2+ exchange by dichlorobenzamil prevented the effects of EGF. Inhibition of voltage-dependent calcium influx by diltiazem also antagonized the effect of EGF. The positive chronotropic action of EGF was significantly enhanced when the concentration of Na+ or Ca2+ was increased in the medium. These data indicate that EGF has a definite dose-dependent effect on the cardiac contractile frequency that is operative through ionic transport mechanisms that include increased calcium entry through voltage-dependent calcium channels and stimulation of Na(+)-H+ and Na(+)-Ca2+ exchange. The similarity in the effects of inhibition of these three ionic mechanisms suggests they are interrelated so that interference at any step in the process inhibits the action of EGF on cardiac myocytes.

The effect of amiloride and its analog dichlorobenzamil on the cardiac chronotropic responses of myocardial cell aggregates in culture to alterations of extracellular potassium or calcium

1. Cardiac ventricular myocytes aggregates from 7-day-old chick embryos show a decrease in beating rate with increasing [K+]0, from 1 to 10 mM, and stop beating at 10 mM. 2. Amiloride, at 10(-7) and 10(-6) M, produced a significant (P less than 0.05) accentuation of the effects of increasing [K]0 that were dose dependent and produced an earlier cessation of spontaneous beating. 3. The amiloride analogue 3',4'-dichlorobenzamil (DCB), that preferentially inhibits Na+/Ca2+ exchange, produced a significant (P less than 0.05) accentuation of the effects of [K+]0 that were greater than that produced by amiloride. 4. When [Ca]0 was increased from 2.2 to 5.0 mM, cardiac beating rate increased, became irregular and then stopped at [Ca2+]0 of 5 mM. 5. DCB, but not amiloride, significantly (P less than 0.05) accentuated the changes with increasing [Ca2+]0. Thus inhibition of Na+-Ca2+ exchange accentuates the effect of increased [Ca]0 on the heart.

Characterization of rat heart plasma membrane Ca2+/Mg2+ ATPase

The Ca2+/Mg2+ ATPase of rat heart plasma membrane was activated by millimolar concentrations of Ca2+ or Mg2+; other divalent cations also activated the enzyme but to a lesser extent. Sodium azide at high concentrations inhibited the enzyme by about 20%; oligomycin at high concentrations also inhibited the enzyme slightly. Trifluoperazine at high concentrations was found inhibitory whereas trypsin treatment had no significant influence on the enzyme. The rate of ATP hydrolysis by the Ca2+/Mg2+ ATPase decayed exponentially; the first-order rate constants were 0.14-0.18 min-1 for Ca2+ ATPase activity and 0.15-0.30 min-1 for Mg2+ ATPase at 37 degrees C. The inactivation of the enzyme depended upon the presence of ATP or other high energy nucleotides but was not due to the accumulation of products of ATP hydrolysis. Furthermore, the inactivation of the enzyme was independent of temperature below 37 degrees C. Con A when added into the incubation medium before ATP blocked the ATP-dependent inactivation; this effect was prevented by alpha-methylmannoside. In the presence of low concentrations of detergent, the rate of ATP hydrolysis was reduced while the ATP-dependent inactivation was accelerated markedly. Both Con A and glutaraldehyde decreased the susceptibility of Ca2+/Mg2+ ATPase to the detergent. These results suggest that the Ca2+/Mg2+ ATPase is an intrinsic membrane protein which may be regulated by ATP.

The effect of epidermal growth factor on chronotropic response in cardiac cells in culture

Cardiac chronotropic response to epidermal growth factor (EGF) was assessed in chick embryonic ventricular cell aggregates. EGF at a concentration of 10 ug/mL but not at 5 ug/mL produced a significant (p less than 0.05) increase in cardiac beating rate. This was evident within 10 min, reached a peak at about 15 min and remained at that level for 1.5 hr or the rest of the observation period. The effect of EGF on cardiac automaticity was reduced but not abolished at a lower temperature (22oC) that is known to decrease the affinity of the EGF receptor and reduce the internalization of EGF. Hypothermia did not change the maximum increase in heart rate response from isoproterenol although it altered the pattern of the response. Beta adrenoreceptor blockade with metoprolol only slightly altered the response to EGF. These data indicate that EGF produces functional effects on the heart that may be mediated through EGF receptor linked mechanisms.

Inhibition of a voltage-dependent Ca current by concanavalin A

Incubation of the hypotrichous ciliate Stylonychia mytilus in fluorescein-labeled concanavalin A (Con A, 0.1-0.5 microgram/ml) produced a strong fluorescence of its membranelles, but comparatively weak fluorescence of the other compound cilia and of the somatic membrane. Compared to untreated cells, the frequency of spontaneous backward movements was reduced in the presence of 0.5 microgram/ml ConA. In electrophysiological experiments Con A altered the excitability of the cell membrane. The two-peak action potential lost its second component which is associated with voltage-dependent Ca channels in the membranelles. The corresponding Ca current (Ca current I) was inhibited by low concentrations of Con A (0.2-0.5 microgram/ml). A second voltage-dependent Ca current (Ca current II) was not affected. Reducing the K outward current by intracellular Cs and/or extracellular tetraethylammonium, or changing the holding potential, did not restore the Con A-sensitive Ca current I. Con A also inhibited this current when Ca was replaced by Ba. The inhibitory effect of Con A on the voltage-dependent Ca current I was prevented by 10-30 mM alpha-methyl-D-mannoside, and the lectin wheat germ agglutinin (20 micrograms/ml) did not affect the Ca currents, indicating that the Con A effect was mediated by binding to specific sugar residues on the excitable membrane. The succinylated dimeric derivative of Con A did not inhibit Ca current I up to concentrations of 5 micrograms/ml. It is concluded that the two voltage-dependent Ca currents in Stylonychia can be chemically isolated due to their different sensitivity to Con A, which appears to bind preferentially to sites near or at the Ca channel in the membranellar membrane.