Reversal of cisplatin resistance by neferine/isoliensinine and their combinatorial regimens with cisplatin-induced apoptosis in cisplatin-resistant colon cancer stem cells (CSCs)

Cisplatin chemotherapy to the colorectal cancer cells (CRCs) is accompanied by dose-limiting adverse effects along with the acquisition of drug resistance implicating low therapeutic outcomes. The present study is aimed to evaluate the chemosensitizing efficacy of neferine/isoliensinine or combinatorial regimen of neferine/isoliensinine with cisplatin against CSCs (cisplatin resistant colon stem cells). CSCs were developed using pulse exposure of cisplatin to parental HCT-15 cells. Neferine/isoliensinine or combinatorial regimens of Neferine/isoliensinine and cisplatin exhibited a stronger cytotoxic activity against CSCs compared to control. IC₅₀ doses were found to be 6.5 μM for neferine, 12.5 μM for isoliensinine, and 120 μM for cisplatin respectively. Furthermore, the combinatorial regimen of a low dose of cisplatin (40 μM) with 4 μM neferine/8 μM isoliensinine induced cell death in a synergistic manner as described by isobologram. Neferine/isoliensinine could confer extensive intracellular reactive oxygen species generation in CSCs. Neferine/isoliensinine or combinatorial regimens dissipated mitochondrial membrane potential and enhanced intracellular [Ca²⁺ ]i, which were measured by spectroflurimetry. Furthermore, these combinatorial regimens induced a significant increase in the sub G0 phase of cell cycle arrest and PI uptake and alleviated the expression of ERCC1 in CSCs. Combinatorial regimens or neferine/isoliensinine treatments downregulated the cell survival protein expression (PI3K/pAkt/mTOR) and activated mitochondria-mediated apoptosis by upregulating Bax, cytochrome c, caspase-3, and PARP cleavage expression while downregulating the BCl-2 expression in CSCs. Our study confirms the chemosensitizing efficacy of neferine/isoliensinine or combinatorial regimens of neferine/isoliensinine with a low dose of cisplatin against CSCs.

The Role of Mitochondria in Piperine Mediated Cardioprotection in Isoproterenol Induced Myocardial Ischemia

BACKGROUND

Several pharmacological therapeutic interventions are being used as therapeutic agents against myocardial infarction/ischemia (MI) but their usage is constrained by toxicity and nonselective pharmacological actions. Our preliminary report depicted the cardioprotective effect of piperine against isoproterenol (ISO)-induced MI.

AIM

Current study determined the protective efficacy of piperine by modulating mitochondrial function in rat models of isoproterenol (ISO)-induced myocardial ischemia.

METHODS

The above aim was achieved by analyzing mitochondrial antioxidant status, mitochondrial calcium, mitochondrial enzyme activity, ATP level, and apoptosis. Ultra-structural alterations in heart tissue were determined by TEM analysis. RT-PCR studies, Western blotting were executed to determine apoptotic & proapoptotic gene expression, and apoptotic protein expression respectively.

RESULTS

The results elucidate that piperine pre-treatment prevents ISO induced alterations in the mitochondrial antioxidant status, Krebs cycle as well as mitochondrial respiratory chain enzyme activities (MRCEs). ISO induced ultra-structural changes of heart mitochondria were significantly reduced in the group received piperine pretreatment followed by ISO injection. Piperine maintains mitochondrial calcium homeostasis and inhibits ISO-induced myocardial apoptosis. A significant increase in the expression levels of proapoptotic genes such as Bax, caspases (caspase 9, caspase 3), cytochrome-c with concomitant decrease in Bcl-2 expression (anti-apoptotic gene) was observed in ISO injected group compared to control group. Group received the piperine pretreatment followed by ISO administration has showed a significant decrease in the expression profile of proapoptotic genes with concomitant increase in the anti-apoptotic gene expression than ISO injected group. Apoptotic protein expressions including Bax, cytochrome-c, caspase-3, and cleaved PARP were upregulated & Bcl-2 was downregulated with ISO treatment whereas piperine pre-treatment prevented these changes in apoptotic protein expressions during ISO-induced myocardial cell damage.

CONCLUSION

Current results demonstrate the piperine efficacy for attenuating ISO-induced myocardial ischemia by enhancing mitochondria function. This study described that the piperine could be used as a nutritional intervention against ISO-induced myocardial ischemia.

Thrombin-dependent calcium signalling in single human erythroleukaemia cells

1. A combination of single cell fluorescence and patch clamp techniques were used to study the mechanisms underlying thrombin-evoked Ca2+ signals in human erythroleukaemia (HEL) cells, a leukaemic cell line of platelet-megakaryocyte lineage. 2. Thrombin caused a transient increase in intracellular Ca2+ ([Ca2+]i), consisting of both release of Ca2+ from intracellular stores and influx of extracellular Ca2+. Mn2+ quench studies indicated that the thrombin-evoked divalent cation-permeable pathway was activated during, but not prior to, release from internal stores. 3. Thapsigargin (1 microM) irreversibly released internal Ca2+ from the same store as that released by thrombin and continuously activated a Ca(2+)-influx mechanism. The amplitude of the thrombin- and thapsigargin-induced Ca2+ influx displayed a marked single cell heterogeneity which showed no correlation with the size of the store Ca2+ transient. 4. In whole-cell patch clamp recordings, both thrombin and thapsigargin evoked an inwardly rectifying Ca2+ current which developed with little or no increase in current noise, showed no reversal in the voltage range -110 to +60 mV and was blocked by 1 mM Zn2+. The apparent divalent cation permeability sequence of this pathway was Ca2+ > > Ba2+ > Mn2+, Mg2+. The thapsigargin-evoked current density at -100 mV varied between 0.42 and 2.1 pA pF-1 in different cells. Thrombin failed to activate additional Ca2+ current if it was added after the thapsigargin-induced inward current had fully developed. 5. These studies indicate that thrombin activates Ca2+ influx in HEL cells entirely via a Ca(2+)-store-release-activated Ca2+ current (Icrac) rather than via receptor-operated or second messenger-dependent Ca2+ channels. The level of expression of Icrac appears to be a major factor in determining the duration of the thrombin-evoked [Ca2+]i response and therefore represents a means by which cells can exert control over [Ca2+]i-dependent events.

Fcgamma receptor I activation triggers a novel Ca2+-activated current selective for monovalent cations in the human monocytic cell line, U937

Previous reports have suggested that receptors for immunoglobulin G (IgG), FcgammaRs, directly activate a nonselective cation channel (Young, J. D.-E., Unkeless, J. C., Young, T. M., Mauro, A., and Cohn, Z. A. (1983) Nature 306, 186-189; Nelson, D. J., Jacobs, E. R., Tang, J. M., Zeller, J. M., and Bone, R. C. (1985) J. Clin. Invest. 76, 500-507). To investigate the mechanisms underlying membrane conductance changes following human high affinity (FcgammaRI) receptor activation, we have used the human monocytic cell line U937 and combined conventional whole cell patch-clamp recordings with single cell fura-2 Ca2+ measurements. Using a K+-free internal solution, antibody cross-linking of IgG-occupied FcgammaRI activated an inward current at negative potentials, whose amplitude and time course mirrored the concomitant rise in intracellular Ca2+. Current-voltage relationships, obtained under different ionic conditions, revealed a monovalent cation-selective conductance that, under physiological conditions, would result in Na+ influx. Noise analysis of current recordings indicated a single channel conductance of 18 picosiemens and a mean opening time of 4.5 ms. This current was also activated by rises in intracellular Ca2+ induced by ionomycin (3 microM) or thapsigargin (1 microM). Addition of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid to the intracellular medium abolished any channel activation by ionomycin, FcgammaRI, or the low affinity receptor, FcgammaRII. These results demonstrate that FcgammaRI activation triggers a novel Ca2+-activated channel selective for monovalent cations and that neither FcgammaRI nor FcgammaRII can directly activate a channel.

Temperature-dependent block of capacitative Ca2+ influx in the human leukemic cell line KU-812

The mechanism by which depletion of intracellular Ca2+ stores activates Ca2+ influx is not understood. We recently showed that primaquine, an inhibitor of vesicular transport, blocks the activation of the calcium release-activated calcium current (ICRAC) in rat megakaryocytes (Somasundaram, B., Norman, J. C., and Mahaut-Smith, M. P. (1995) Biochem. J. 309, 725-729). Since it is well established that vesicular transport is temperature-sensitive, we have investigated the effect of temperature on both the activation and maintenance of store-mediated Ca2+ and Mn2+ influx in the human leukemic cell line KU-812 using a combination of whole cell ICRAC recordings and measurements of Mn2+ photoquench of fura-2. Activation of ICRAC was temperature-sensitive, showing a nonlinear reduction when the temperature was lowered from 27 to 17 degrees C with an abrupt change at 21-22 degrees C and complete inhibition at 17 degrees C. Once activated, ICRAC also displayed an abrupt reduction at 21-22 degrees C but was not completely blocked even when the temperature was reduced to 14 degrees C, suggesting that at least one of the temperature-sensitive components is exclusively involved in ICRAC activation. Activation of store-mediated Mn2+ influx also showed similar nonlinear temperature sensitivity and complete inhibition at 19 degrees C. However, in contrast to ICRAC measurements, lowering the temperature following maximal activation of the influx pathway at 37 degrees C did not result in any detectable residual Mn2+ entry below 19 degrees C. We conclude that the mechanism of store-mediated Ca2+ influx involves temperature-dependent steps in both its maintenance and activation, suggesting dependence on a lipid membrane environment.

Differentiation of the human monocytic cell line U937 results in an upregulation of the calcium release-activated current, ICRAC

1. Single cell fura-2 fluorescence measurements and whole-cell patch clamp recordings were used to investigate the effects of macrophage-like differentiation, induced by dibutyryl cAMP (dbcAMP), on Ca2+ influx triggered by Ca2+ store depletion in the human monocytic cell line, U937. 2. In differentiated cells, the rise in intracellular [Ca2+] following store depletion by thapsigargin (TG) in nominally Ca(2+)-free solution was 94% greater and the [Ca2+]i rise on subsequent re-addition of external Ca2+ (2 mM) was 292% greater than in undifferentiated cells. 3. Under conditions where [Ca2+]i was buffered by BAPTA, TG-induced store depletion failed to activate a detectable inward Ca2+ current in undifferentiated U937 cells. Under identical conditions, store depletion of differentiated U937 cells generated an inwardly rectifying Ca(2+)-selective current which showed no reversal from -140 to +30 mV and was blocked by 1 microM external La3+; characteristics of the calcium release-activated Ca2+ current (ICRAC) identified in other cells. 4. We conclude that U937 cells show a differentiation-dependent upregulation of a store-mediated Ca2+ entry pathway, identified as ICRAC, which is not correlated with the small associated increase in the size of TG-sensitive Ca2+ pools.

Calcium waves in fluid flow stimulated osteoblasts are G protein mediated

Calcium (Ca2+) entry upon cell perturbation has been examined in transformed human osteoblast cells (U-2/OS). The cells were deformed by fluid flow from a patch pipette held in proximity to the cell by applying a positive pressure (+50 mm Hg) for the passage of saline over the membrane. Intracellular calcium [Ca2+]i was examined following loading with 5 microM Fura-2 AM. The changes in ratio were determined at 330-ms intervals. Waves of [Ca2+]i were seen spreading along the length of the individual cell following stimulation (n = 30). The initial change in Ca2+ at the site of stimulation occurred within 660 ms after applying the stimulus. Following 1.3 (+/- 0.33) s of raised [Ca2+]i, the values returned to those of predeformation. The Ca2+ response following fluid flow stimulation was blocked by 300 microM Cd2+, a specific blocker of Ca2+ channels, demonstrating an extracellular source of Ca2+. Preincubation with cholera toxin (250 ng/ml for 6 h) prolonged the elevation of Ca2+ induced by fluid flow stimulation (n = 20). In contrast, pertussis toxin (250 ng/ml for 6 h) completely eliminated the Ca2+ response to fluid flow stimulation (n = 20). Cells maintained in solutions free of Ca2+ demonstrated no change in [Ca2+]i. Tetraethylammonium (6 mM) had no effect on the response (n = 10). In addition pretreatment with ryanodine (2 and 10 microM; each group n = 10) in media showed a reduced wave of Ca2+ in response to mechanical deformation. The response to a phospholipase C inhibitor also eliminated the response to the mechanical deformation (n = 10). In addition cells that demonstrated changes in Ca(2+)-containing media lost the ability to respond when EGTA was added to the media. Following this, 2 microM ryanodine was added to the cells, demonstrating a response too small to replicate the fluid flow stimulated wave, but supporting the view that the cells were vital following preincubation.

IgG-induced Ca2+ oscillations in differentiated U937 cells; a study using laser scanning confocal microscopy and co-loaded fluo-3 and fura-red fluorescent probes

We have investigated, at the single cell level, intracellular Ca2+ ([Ca2+]i) modulations triggered by the high affinity receptor for IgG, Fc gamma RI, in the monocytic cell line, U937. Cells were co-loaded with the Ca(2+)-sensitive dyes, Fluo-3 and Fura-Red, by incubation with their acetoxymethyl (AM) esters and confocal ratio imaging was used to monitor the [Ca2+]i changes induced by antibody cross-linking of IgG-loaded Fc gamma RI. A single Ca2+ spike was observed in 81% of untreated cells whereas dibutyryl cAMP-induced differentiation into a more macrophage cell type resulted in a sub-population of cells (44%) responding to receptor cross-linking with calcium oscillations. This change in calcium signalling may explain the difference in functional responses triggered by Fc gamma RI in monocytes and macrophages. Analysis of the Fluo-3 and Fura-Red fluorescence, after AM-ester loading, showed that both dyes have similar photobleach rates and intracellular localization allowing compensation for shifts in focal plane, dye photobleaching and non-uniformity of dye loading. In addition, because the binding kinetics of both dyes are equivalent, accurate temporal information can be gained about [Ca2+] changes. There are, however, two major problems with this dual indicator technique. Firstly, loading from AM esters results in considerable variation between cells in the intracellular concentration ratio of the two dyes, making calibration difficult. Secondly, the fluorescence ratio, Fluo-3/Fura-Red, behaves non-linearly at Ca2+ concentrations less than approximately 500 nM and comparison with Fura-2-loaded single cell photometry studies suggests there is considerable amplitude distortion of the signal when the ratios are displayed on a linear scale. These problems may considerably limit the application of Fluo-3/Fura-Red ratiometric measurements.

Primaquine, an inhibitor of vesicular transport, blocks the calcium-release-activated current in rat megakaryocytes

The whole-cell patch-clamp technique was used to study the effect of primaquine, an inhibitor of vesicular transport, on the calcium-release-activated current (Icrac) in rat megakaryocytes. Addition of primaquine, before emptying of internal Ca2+ stores by ionomycin, prevented the development of Icrac, with a half-maximal concentration of near 100 microM. Maximal inhibition (> or = 83%) was observed at 0.6-1 mM primaquine. At 1 mM, chloroquine, a related compound which is less effective at blocking vesicular secretion, had no effect on Icrac. Primaquine (0.8 mM) added after sustained activation of Icrac caused a gradual block of current, with maximal inhibition of 50% observed after 2-3 min. At 1 mM, internal guanosine 5'-[gamma-thio]triphosphate reduced Icrac by 65 +/- 13%. Neither 1 mM GTP nor 2 mM guanosine 5'-[beta-thio]diphosphate had any significant effect on Icrac. The recognized role of GTPases in the regulation of vesicular trafficking, together with block of Icrac activation by primaquine, provide evidence that the channels carrying Icrac may be stored in a vesicular membrane compartment and transferred to the plasma membrane following store depletion.

A novel monovalent cation channel activated by inositol trisphosphate in the plasma membrane of rat megakaryocytes

The activation of a monovalent cation current was studied in rat megakaryocytes using patch clamp techniques combined with photometric measurements of intracellular concentrations of Ca2+ ([Ca2+]i) and Na+. ADP evoked a release of [Ca2+]i and transiently activated a monovalent cation-selective channel, which, at negative potentials and under physiological conditions, would be expected to carry an inward Na+ current. The single channel conductance, estimated by noise analysis from whole cell currents at -50 to -60 mV was 9 picosiemens. Thapsigargin-induced [Ca2+]i increases failed to stimulate the monovalent cation current, suggesting that neither [Ca2+]i nor the depletion of internal Ca2+ stores were activators of this conductance. However, buffering of [Ca2+]i changes with 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid showed that both activation and inactivation of the current were accelerated by a rise in [Ca2+]i. The monovalent cation conductance was activated by internal perfusion with inositol 1,4,5-trisphosphate, both in the presence and in the absence of a rise in [Ca2+]i. Internal perfusion with inositol 2,4,5-trisphosphate, the poorly metabolizable isomer of inositol trisphosphate, similarly activated the monovalent cation current, whereas 1,3,4,5-tetrakisphosphate neither activated a current nor modified the ADP-induced monovalent current. Heparin, added to the pipette, blocked activation of the channel by ADP. The intracellular concentration of Na+, monitored by sodium-binding benzofuran isopthalate, increased by 10-20 mM in response to ADP under pseudophysiological conditions. We conclude the existence of a novel nonselective cation channel in the plasma membrane of rat megakaryocytes, which is activated by IP3 and can lead to increases in cytosolic Na+ after stimulation by ADP.

Three cation influx currents activated by purinergic receptor stimulation in rat megakaryocytes

1. Simultaneous patch clamp and fura-2 fluorescence measurements were used to study ATP-evoked membrane currents and intracellular [Ca2+] ([Ca2+]i) changes in rat megakaryocytes. 2. At negative potentials, under conditions that blocked K+ currents, 20 microM ATP activated a biphasic inward current and a concurrent biphasic increase in [Ca2+]i. The initial [Ca2+]i increase was due to Ca2+ influx whereas the delayed (1.70 +/- 0.13 s, mean +/- S.D.) increase was at least partly due to the release of internal Ca2+ stores. 3. The initial current was activated within 100 ms, inactivated within 1-4 s and was carried by both Na+ and Ca2+. 4. The delayed current was also transient and carried mainly by Na+ when Ca2+ buffering in the pipette was low. This Na+ conductance did not require an increase in [Ca2+]i for activation, but was triggered by inositol 1,4,5-trisphosphate (IP3), or a metabolite of IP3. 5. Buffering of [Ca2+]i changes with BAPTA revealed a third current activated by Ca2+ release from internal stores. This channel was selective for divalent cations with the permeability sequence Ca2+ >> Ba2+ > Mn2+, Mg2+. 6. Adenosine-5'-O-3-thiotriphosphate (ATP gamma S), like ATP, evoked all three influx currents, whereas ADP only stimulated Ca2+ release and the two currents associated with it. Increasing the external divalent cation concentration abolished the ATP-evoked Ca2+ release and delayed currents but not the initial transient current. 7. We conclude that rat megakaryocytes express two types of purinergic receptor. One type, activated by ATP, is closely coupled to a non-selective cation channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Isoproterenol and GTP gamma S inhibit L-type calcium channels of differentiating rat skeletal muscle cells

In adult skeletal muscle, G-proteins have been shown to modulate the calcium channels both directly and through a cAMP-dependent phosphorylating mechanism. We have investigated the action of G-proteins on the L-type calcium current in cultured rat muscle cells (myoballs) under voltage clamp in whole cell or perforated patch modes. Intracellular photolytic release of 200 microM GTP gamma S inhibited the L-type calcium current. Inclusion of 500 microM uncaged GTP gamma S in the patch pipette in the whole cell configuration reduced the calcium current by a similar amount. Under perforated patch conditions external application of 10 microM of the beta-adrenergic agonist isoproterenol also reduced the calcium current. Pretreatment of the cells with pertussis toxin reversed the effect of GTP gamma S and removed that of isoproterenol. We conclude that rat myoballs contain beta-adrenergic receptors that inhibit the L-type calcium current, and that this inhibition is mediated by a pertussis toxin-sensitive G-protein.

Experiments on rigor crossbridge action and filament sliding in insect flight muscle

We have explored three aspects of rigor crossbridge action: 1. Under rigor conditions, slow stretching (2% per hour) of insect flight muscle (IFM) from Lethocerus causes sarcomere ruptures but never filament sliding. However, in 1 mM AMPPNP, slow stretching (5%/h) causes filament sliding but no sarcomere ruptures, although stiffness equals rigor values. Thus loaded rigor attachments in IFM show no strain relief over several hours, but near-rigor states that allow short-term strain relief indicate different grades of strongly bound bridges, and suggest approaches to annealing the rigor lattice. 2. Sarcomeres of Lethocerus flight muscle, stretched 20-60% and then rigorized, show "hybrid" crossbridge patterns, with overlap zones in rigor, but H-bands relaxed and revealing four-stranded R-hand helical thick filament structure. The sharp boundary exhibits precise phasing between relaxed and rigor arrays along each thick filament. Extrapolating one lattice into the other should allow detailed modeling of the action of each myosin head as it enters rigor. 3. The "A-(bee)-Z problem" exposes a conflict about actin rotational alignment between A-bands and Z-bands of bee IFM, raising the possibility that rigor induction might rotate actins forcefully from one pattern to the other. As Squire noted, 3-D reconstructions of Z-bands in relaxed bee IFM2) imply A-bands where actin target zones form rings rather than helices around thick filaments. However, we confirm Trombitás et al. that rigor crossbridges in bee IFM mark helically arrayed target zones. Moreover, we find that loose crossbridge interactions in relaxed bee IFM mark the same helical pattern. Thus no change of actin rotational alignment by rigor crossbridges seems necessary, but 3-D structure of IFM Z-bands should be re-evaluated regarding the apparent contradiction with A-band symmetry.

Stable transfection of calbindin-D28k into the GH3 cell line alters calcium currents and intracellular calcium homeostasis

Previous work demonstrating the presence and differential distribution of Ca(2+)-binding proteins in the CNS has led to the proposal that cytosolic proteins, such as calbindin-D28k (CB), may play a pivotal role in neurons. We have used a retrovirus containing the full-length cDNA for CB to transfect the pituitary tumor cell line GH3, to generate CB-expressing GH3 cells and to investigate whether ionic channel activities as well as the concentration of intracellular free Ca2+ ([Ca2+]i) homeostasis could be altered by the presence of this Ca(2+)-binding protein. We show that CB-transfected GH3 cells exhibited lower Ca2+ entry through voltage-dependent Ca2+ channels and were better able to reduce [Ca2+]i transients evoked by voltage depolarizations than the wild-type parent cell line. These observations provide a mechanism by which CB may protect tissues against Ca(2+)-mediated excitotoxicity.

GTP gamma S causes contraction of skinned frog skeletal muscle via the DHP-sensitive Ca2+ channels of sealed T-tubules

We have investigated the involvement of G-proteins in excitation-contraction coupling of fast-twitch skeletal muscle, using a fibre preparation designed to retain intact T-tubules and sarcoplasmic reticulum. The nonhydrolysable analogue of guanosine triphosphate, GTP gamma S (50-500 microM) caused a strong, transient isometric contraction in this preparation. Reduction of ethylene-bis(oxonitrilo)tetraacete (EGTA) in the sealed T-tubules from 5 mM to 0.1 mM lowered the threshold to GTP gamma S and removal of sodium reversibly raised it. The dihydropyridine (DHP) calcium channel antagonists nicardipine and nifedipine allowed a first contraction and then blocked subsequent GTP gamma S action. The phenylalkylamine methoxyverapamil (D-600) did likewise, reversibly, at 10 degrees C. The guanosine diphosphate analogue, GDP beta S, and procaine reversibly blocked the action of GTP gamma S; pertussis toxin also blocked it. Photolytic release of 40-100 microM GTP gamma S within 0.1 s from S-caged GTP gamma S caused contraction after a latent period of 0.3-20 s. We conclude that GTP gamma S can activate contraction in frog skeletal muscle via a route requiring both the integrity of the T-tubular DHP-sensitive calcium channel (DHPr) and the presence of sodium in the sealed T-tubules. We propose that in this preparation GTP gamma S activates a G-protein, which in turn activates the DHPr as a calcium channel and releases stored calcium from within the sealed T-tubule. Implications of these results for the excitation-contraction coupling mechanism in skeletal muscle are discussed.

Slip of rabbit striated muscle in rigor or AMPPNP

Single glycerol-extracted rabbit psoas muscle fibres have been slowly extended either in rigor or in the unhydrolysable ATP analogue, AMPPNP, and their sarcomere length, sarcomere structure and tension measured. The length of regularly arrayed sarcomeres, measured by optical diffraction, increased continuously as the muscle was stretched; the maximum sarcomere extension seen was approximately 6%. In the electron microscope sarcomeres from extended muscle fixed in rigor or AMPPNP remained regular in their internal structure, without rupture or obvious lengthening around the Z line. During steady extension at 0.024% per min the tension in the muscle fibre rose until it reached a limiting value [Tm] when the sarcomeres had stretched by 0.8-1.6% and then remained constant with continued extension, while the sarcomeres continued to stretch. Provided that a novel form of preparation of the glycerol-extracted fibres was employed, Tm in rigor was a large fraction of the tension expected from an active isometric muscle fibre. In the presence of AMPPNP Tm was reduced by a factor of 2 to 3. Step extension by 0.08% at 5-min intervals gave the same pattern of mechanical response with similar values of Tm. The isometric tension decay in the interval between the steps was very rapid at first and slowed continuously until the next step. The average speed of tension fall between 30 and 300 s after stretch was measured at each step and plotted relative to the tension in the muscle. The relationship approached linearity, although with a significant upward curvature at high tension.(ABSTRACT TRUNCATED AT 250 WORDS)

The biochemical ecology of Biomphalaria glabrata, a snail host of Schistosoma mansoni: short chain carboxylic and amino acids as phagostimulants

1. A buccal mass olfactometer was used to investigate the responses of the fresh-water pulmonate snail Biomphalaria glabrata to carboxylic and amino acids. 2. The snails proved very discriminating as only 6 (14.6%) of the 41 chemical species tested were effective as phagostimulants. These are ranked as follows in order of potency:- butanoate greater than propanoate greater than D-malate greater than 2-hydroxybutanoate = L-tartrate = L-aspartate. 3. The structure-activity relationships of the active compounds, and their significance to the ecology and control of the snails are discussed.

The effect of zinc on the ultrastructure of the trunk muscle of the larva of Clupea harengus L

The ultrastructural changes in the trunk muscle tissue of Clupea harengus L. larvae, hatched from eggs exposed to four different concentrations of zinc (0.5, 2.0, 6.0 and 12.0 ppm), were examined by morphometric analysis. The surface-to-volume ratio of the mitochondrial cristae was significantly reduced with increasing zinc concentrations. At concentrations of 2.0, 6.0 and 12.0 ppm zinc, the relative volumes of the mitochondria increased significantly and individual mitochondria were swollen. At concentrations 2.0, 6.0 and 12.0 ppm zinc, the relative volumes of the myofibrils decreased significantly. At concentrations of 6.0 and 12.0 ppm zinc the sarcoplasmic reticulum showed significant swelling, and in specimens treated in 12.0 ppm zinc the sarcoplasm contains fewer ribosomes.