Isolation and characterization of mutants defective in seed coat mucilage secretory cell development in Arabidopsis

In Arabidopsis, fertilization induces the epidermal cells of the outer ovule integument to differentiate into a specialized seed coat cell type producing extracellular pectinaceous mucilage and a volcano-shaped secondary cell wall. Differentiation involves a regulated series of cytological events including growth, cytoplasmic rearrangement, mucilage synthesis, and secondary cell wall production. We have tested the potential of Arabidopsis seed coat epidermal cells as a model system for the genetic analysis of these processes. A screen for mutants defective in seed mucilage identified five novel genes (MUCILAGE-MODIFIED [MUM]1-5). The seed coat development of these mutants, and that of three previously identified ones (TRANSPARENT TESTA GLABRA1, GLABRA2, and APETALA2) were characterized. Our results show that the genes identified define several events in seed coat differentiation. Although APETALA2 is needed for differentiation of both outer layers of the seed coat, TRANSPARENT TESTA GLABRA1, GLABRA2, and MUM4 are required for complete mucilage synthesis and cytoplasmic rearrangement. MUM3 and MUM5 may be involved in the regulation of mucilage composition, whereas MUM1 and MUM2 appear to play novel roles in post-synthesis cell wall modifications necessary for mucilage extrusion.

GABA(C) rho(1) subunits form functional receptors but not functional synapses in hippocampal neurons

The ability to control the physiological and pharmacological properties of synaptic receptors is a powerful tool for studying neuronal function and may be of therapeutic utility. We designed a recombinant adenovirus to deliver either a GABA(C) receptor rho(1) subunit or a mutant GABA(A) receptor beta(2) subunit lacking picrotoxin sensitivity [beta2(mut)] to hippocampal neurons. A green fluorescent protein (GFP) reporter molecule was simultaneously expressed. Whole cell patch-clamp recordings demonstrated somatic expression of both bicuculline-resistant GABA(C) receptor-mediated and picrotoxin-resistant GABA(A) receptor-mediated GABA-evoked currents in rho(1)- and beta(2)(mut)-transduced hippocampal neurons, respectively. GABAergic miniature inhibitory postsynaptic currents (mIPSCs) recorded in the presence of 6-cyano-7-nitroquinoxalene-2,3-dione, Mg(2+), and TTX revealed synaptic events with monoexponential activation and biexponential decay phases. Despite the robust expression of somatic GABA(C) receptors in rho(1)-neurons, no bicuculline-resistant mIPSCs were observed. This suggested either a kinetic mismatch between the relatively brief presynaptic GABA release and slow-activating rho(1) receptors or failure of the rho(1) subunit to target properly to the subsynaptic membrane. Addition of ruthenium red, a presynaptic release enhancer, failed to unmask GABA(C) receptor-mediated mIPSCs. Short pulse (2 ms) application of 1 mM GABA to excised outside-out patches from rho(1) neurons proved that a brief GABA transient is sufficient to activate rho(1) receptors. The simulated-IPSC experiment strongly suggests that if postsynaptic GABA(C) receptors were present, bicuculline-resistant mIPSCs would have been observed. In contrast, in beta(2)(mut)-transduced neurons, picrotoxin-resistant mIPSCs were observed; they exhibited a smaller peak amplitude and faster decay compared with control. Confocal imaging of transduced neurons revealed rho(1) immunofluorescence restricted to the soma, whereas punctate beta(2)(mut) immunofluorescence was seen throughout the neuron, including the dendrites. Together, the electrophysiological and imaging data show that despite robust somatic expression of the rho(1) subunit, the GABA(C) receptor fails to be delivered to the subsynaptic target. On the other hand, the successful incorporation of beta(2)(mut) subunits into subsynaptic GABA(A) receptors demonstrates that viral transduction is a powerful method for altering the physiological properties of synapses.

Isolation and characterization of mutants defective in seed coat mucilage secretory cell development in Arabidopsis

In Arabidopsis, fertilization induces the epidermal cells of the outer ovule integument to differentiate into a specialized seed coat cell type producing extracellular pectinaceous mucilage and a volcano-shaped secondary cell wall. Differentiation involves a regulated series of cytological events including growth, cytoplasmic rearrangement, mucilage synthesis, and secondary cell wall production. We have tested the potential of Arabidopsis seed coat epidermal cells as a model system for the genetic analysis of these processes. A screen for mutants defective in seed mucilage identified five novel genes (MUCILAGE-MODIFIED [MUM]1-5). The seed coat development of these mutants, and that of three previously identified ones (TRANSPARENT TESTA GLABRA1, GLABRA2, and APETALA2) were characterized. Our results show that the genes identified define several events in seed coat differentiation. Although APETALA2 is needed for differentiation of both outer layers of the seed coat, TRANSPARENT TESTA GLABRA1, GLABRA2, and MUM4 are required for complete mucilage synthesis and cytoplasmic rearrangement. MUM3 and MUM5 may be involved in the regulation of mucilage composition, whereas MUM1 and MUM2 appear to play novel roles in post-synthesis cell wall modifications necessary for mucilage extrusion.

Fimbria-mediated bacterial adhesion to human oral epithelium

Oral mucosa biopsies and saliva samples from 12 individuals were processed for transmission (TEM) and scanning (SEM) electron microscopy with and without ruthenium red staining. Additionally performed microbiological estimations indicated in all bacteriological samples a facultative pathogenic flora. SEM and TEM investigation showed a diverse bacterial flora attached to the mucosal surface. Fimbriae comprising the glycocalyx and enabling bacterial attachment to the epithelial cells could be clearly visualised by ruthenium red. The only mode of bacterial attachment to the oral mucosa detected in the present investigation was fimbria-mediated adhesion and co-adhesion. The fimbria-mediated adhesion enables the bacterial persistence in the oral cavity and is the first step in the bacterial colonisation process.

Influence of calcitonin gene-related peptide release on pH-induced mechanical depression in rat atria

Rat atria is richly innervated by sensory nerve fibers that release CGRP when stimulated either by capsaicin or acid pH. We studied the physiological relevance of acid pH-induced CGRP release on changes in atrial contractility and relaxation produced by lowering the pH. Isolated atria electrically paced at 2.77 Hz were exposed to a 10-minute period of metabolic acidosis (pH=6.73+/-0.01, n=28) after: 1) CGRP release induced by capsaicin 0.5 microM; 2) blockage of CGRP release with ruthenium red (RR) 5 microM; 3) no pretreatment; and 4) CGRP receptor blockage with CGRP(8-37) 1 microM. Contractility and relaxation were significantly less depressed by acid pH when CGRP release was prevented by RR or CGRP receptor activation was blocked by CGRP(8-37). The results suggest that CGRP release and the activation of CGRP receptors may be physiologically involved in contributing to the depression of contractility and relaxation induced by acid pH in rat atria.

Demonstration of biofilm in infectious crystalline keratopathy using ruthenium red and electron microscopy

OBJECTIVE

Bacterial biofilm formation has been implicated in the pathogenesis of infectious crystalline keratopathy. Biofilm cannot be visualized by electron microscopy without the addition of a fixative that stabilizes the polysaccharide-rich bacterial extracellular matrix that surrounds the bacterial colonies in a biofilm. We used ruthenium red as a fixative to evaluate corneal biopsy specimens for the presence of bacterial biofilm in three cases of infectious crystalline keratopathy (ICK) and five cases of chronic microbial keratitis without crystalline changes.

DESIGN

Case series with clinicopathologic correlation.

PARTICIPANTS

Eight patients underwent corneal biopsy or therapeutic keratoplasty as part of their management for chronic unresponsive microbial keratitis.

METHODS

The corneal specimens removed were trisected for microbiology, pathology, and transmission electron microscopy (TEM). The TEM specimens were fixed in 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer with 0.05% ruthenium red.

MAIN OUTCOME MEASURES

Demonstration of bacterial biofilm with TEM.

RESULTS

TEM demonstrated organisms with a surrounding extracellular matrix consistent with a bacterial biofilm in the three cases of ICK but not in the five other cases of chronic microbial keratitis.

CONCLUSIONS

The presence of biofilm in ICK can be demonstrated with TEM with appropriate fixation techniques that stabilize the bacterial extracellular matrix. Biofilm stains intensely with periodic acid-Schiff because of the polysaccharide-rich extracellular matrix and weakly with Gram stain because of the high proportion of nonviable organisms. Biofilm formation occurs in ICK but probably not in chronic bacterial keratitis without crystalline changes. Secretion of an extracellular matrix by bacteria to form a biofilm is a response to a nutrient-deprived environment in which growth and replication is depressed. The extracellular matrix of the biofilm may mask bacterial antigens, explaining the relative lack of inflammatory response in these infections. It may also be one of the mechanisms explaining the resistance to in vivo antimicrobial therapy when in vitro sensitivities have been proven.

IP3-gated channels and their occurrence relative to CNG channels in the soma and dendritic knob of rat olfactory receptor neurons

Olfactory receptor neurons respond to odorants with G protein-mediated increases in the concentrations of cyclic adenosine 3',5'-monophosphate (cAMP) and/or inositol-1,4,5-trisphosphate (IP3). This study provides evidence that both second messengers can directly activate distinct ion channels in excised inside-out patches from the dendritic knob and soma membrane of rat olfactory receptor neurons (ORNs). The IP3-gated channels in the dendritic knob and soma membranes could be classified into two types, with conductances of 40 +/- 7 pS (n = 5) and 14 +/- 3 pS (n = 4), with the former having longer open dwell times. Estimated values of the densities of both channels from the same inside-out membrane patches were very much smaller for IP3-gated than for CNG channels. For example, in the dendritic knob membrane there were about 1000 CNG channels x microm(-2) compared to about 85 IP3-gated channels x microm(-2). Furthermore, only about 36% of the dendritic knob patches responded to IP3, whereas 83% of the same patches responded to cAMP. In the soma, both channel densities were lower, with the CNG channel density again being larger ( approximately 57 channels x microm(-2)) than that of the IP3-gated channels ( approximately 13 channels x microm(-2)), with again a much smaller fraction of patches responding to IP3 than to cAMP. These results were consistent with other evidence suggesting that the cAMP-pathway dominates the IP3 pathway in mammalian olfactory transduction.

The rapid mode of calcium uptake into heart mitochondria (RaM): comparison to RaM in liver mitochondria

A mechanism of Ca(2+) uptake, capable of sequestering significant amounts of Ca(2+) from cytosolic Ca(2+) pulses, has previously been identified in liver mitochondria. This mechanism, the Rapid Mode of Ca(2+) uptake (RaM), was shown to sequester Ca(2+) very rapidly at the beginning of each pulse in a sequence [Sparagna et al. (1995) J. Biol. Chem. 270, 27510-27515]. The existence and properties of RaM in heart mitochondria, however, are unknown and are the basis for this study. We show that RaM functions in heart mitochondria with some of the characteristics of RaM in liver, but its activation and inhibition are quite different. It is feasible that these differences represent different physiological adaptations in these two tissues. In both tissues, RaM is highly conductive at the beginning of a Ca(2+) pulse, but is inhibited by the rising [Ca(2+)] of the pulse itself. In heart mitochondria, the time required at low [Ca(2+)] to reestablish high Ca(2+) conductivity via RaM i.e. the 'resetting time' of RaM is much longer than in liver. RaM in liver mitochondria is strongly activated by spermine, activated by ATP or GTP and unaffected by ADP and AMP. In heart, RaM is activated much less strongly by spermine and unaffected by ATP or GTP. RaM in heart is strongly inhibited by AMP and has a biphasic response to ADP; it is activated at low concentrations and inhibited at high concentrations. Finally, an hypothesis consistent with the data and characteristics of liver and heart is presented to explain how RaM may function to control the rate of oxidative phosphorylation in each tissue. Under this hypothesis, RaM functions to create a brief, high free Ca(2+) concentration inside mitochondria which may activate intramitochondrial metabolic reactions with relatively small amounts of Ca(2+) uptake. This hypothesis is consistent with the view that intramitochondrial [Ca(2+)] may be used to control the rate of ADP phosphorylation in such a way as to minimize the probability of activating the Ca(2+)-induced mitochondrial membrane permeability transition (MPT).

Citrinin-induced mitochondrial permeability transition

The effects of mycotoxin citrinin on Ca2+ efflux and membrane permeabilization were studied in isolated rat liver mitochondria. The efflux rate observed when in presence of ruthenium red was higher when citrinin was added. Swelling experiments demonstrated Ca(2+)-dependent membrane permeabilization by citrinin. Catalase, butylhydroxitoluene (BHT), and dithiothreitol (DTT) did not protect swelling caused by Ca2+ plus citrinin. The protection conferred by ATP-Mg2+ and cyclosporin A in the latter experiments are strong indications of pore formation. These results suggest that citrinin can induce permeability transition by a mechanism that does not involve oxidative damage.

Opisthorchis viverrini: ultrastructure and cytochemistry of the glycocalyx of the tegument

The ultrastructure and cytochemistry of the glycocalyx of the tegument of Opisthorchis viverrini during maturation from newly excysted juvenile to adult stages were investigated using colloidal iron, ruthenium red and lectin stainings. The results showed that the glycocalyx was intensely stained by the first two dyes, thus indicating the presence of relatively high amounts of negative charges. However, the thickness and intensity of the staining decreased during the fluke's maturation. Binding studies using lectin probes on the surface of adult parasites showed that binding sites for Canavalia ensiformis (Con A), Triticum vulgaris (WGA) and Ricinus communis I (RCA I) were present in relative large amounts on the glycocalyx of the adult tegument, whereas those for Dolichos biflorus (DBA) were relatively fewer in number, and those for Ulex europaeus I (UEA I) were absent. The binding patterns of Con A, WGA, RCA I and DBA were generally similar, and the reaction product was uniformly distributed over the dorsal and ventral surfaces of the parasite's body. These bindings, therefore, indicate the presence of D-mannose/D-glucose, N-acetyl-D-glucosamine/sialic acid, D-galactose and N-acetyl-D-galactosamine residues on the glycocalyx of the adult tegument.

Responses to putative second messengers and odorants in water nose olfactory neurons of Xenopus laevis

Using the whole-cell mode of the patch-clamp technique, we attempted to record inward currents in response to cAMP, inositol 1,4, 5-trisphosphate (IP(3)) and odorants from sensory neurons in the olfactory epithelium of the Xenopus laevis lateral diverticulum (water nose). Dialysis of 100 microM of IP(3) induced inward currents, while dialysis of 1 mM of cAMP into olfactory neurons did not induce any response under the voltage-clamp conditions. Changes in membrane conductance were examined by applying ramp pulses. The slope of the current-voltage (I-V) curve during the IP(3)-induced response was steeper than that after the response, indicating that IP(3) increased the membrane conductance. The water nose olfactory neurons have been shown to respond to both amino acids and volatile odorants. The slopes of I-V curves during responses to amino acids and a volatile odorant, lilial, were similar to those before the responses, suggesting that the total membrane conductance was not changed during responses to amino acids and the volatile odorant.

Differential quantal release of histamine and 5-hydroxytryptamine from mast cells of vesicular monoamine transporter 2 knockout mice

The recent availability of mice lacking the neuronal form of the vesicular monoamine transporter 2 (VMAT2) affords the opportunity to study its roles in storage and release. Carbon fiber microelectrodes were used to measure individual secretory events of histamine and 5-hydroxytryptamine (5-HT) from VMAT2-expressing mast cells as a model system for quantal release. VMAT2 is indispensable for monoamine storage because mast cells from homozygous (VMAT2(-/-)) mice, while undergoing granule-cell fusion, do not release monoamines. Cells from heterozygous animals (VMAT2(+/-)) secrete lower amounts of monoamine per granule than cells from wild-type controls. Investigation of corelease of histamine and 5-HT from granules in VMAT2(+/-) cells revealed 5-HT quantal size was reduced more than that of histamine. Thus, although vesicular transport is the limiting factor determining quantal size of 5-HT and histamine release, intragranular association with the heparin matrix also plays a significant role.

Dynamic changes in sarcoplasmic reticulum function in cardiac hypertrophy and failure

Previous studies have demonstrated that cardiac function changes with development of pressure overload-induced hypertrophy. The present study was undertaken to discover the basis for the changes in sarcoplasmic reticulum (SR) functions: uptake, (as related to the SR Ca2+ pump properties) and release in isolated, perfused hypertrophied rat hearts. Our results demonstrated significant prolongation of the time-to-90%-relaxation, both during the period of compensation (8 weeks after banding the ascending aorta, group HR1), when systolic function was preserved, and later with progressive hypertrophy (20 weeks after banding, group HR2) and contractile failure (20-22 weeks after banding, group F). The initial rates of the oxalate-supported SR Ca2+ uptake and the maximum transport rate (Vmax) of the SR Ca2+ pump, measured in the left ventricular homogenates, during blockade of the SR Ca2+ release channels with ruthenium red, were preserved in group HR1. To correlate early relaxation abnormalities with SR function, the [Ca2+] required for half-maximal pump activation (EC50) was examined and increased significantly in HRI vs. Sham1 (0.95+/-0.06 vs. 0.81+/-0.04 microM, P<0.05) indicating that the affinity of the SR Ca2+ pump for Ca2+ was reduced. The same tendency was demonstrated in groups HR2 (0.94+/-0.06 vs. 0.79+/-0.05) and F (0.89+/-0.05 vs. 0.78+/-0.05). In addition, with progression of hypertrophy we observed a significant decline in the amount of SR Ca2+ pump, as assessed by the Vmax, from 31.22+/-1.20 (Sham2) to 26.47+/-1.58 HR2) nmol/mg protein per min (P<0.05), and from 33.81+/-1.23 (Sham3) to 25.15+/-1.57 (F) nmol/mg protein per min, (P<0.01). This decrease was accompanied by a parallel reduction in the number of SR Ca2+ release channels by 14% (HR2) and 23% (F), as determined by maximum [3H] ryanodine binding (Bmax). These results suggest that pressure overload-induced changes in SR Ca2+ uptake (as reflected by Vmax and EC50) and SR Ca2+ release (as reflected by Bmax), both leading to diminished Ca2+ sequestration, may contribute to impaired cardiac relaxation with compensatory hypertrophy and failure.

The effects of cold-restraint stress on urinary bladder wall compared with interstitial cystitis morphology

Stress is associated with many diseases of unknown aetiology. This study demonstrates the effects of cold-restraint stress on the morphology of the urinary bladder. Additionally, it compares the results obtained with the morphology of the interstitial cystitis. The animals were subjected to three hours of cold-restraint stress and then starved for 48 h. The morphology and histochemistry of the urinary bladder was investigated with light and electron microscopy. The proliferative activity was analysed via flow cytometry. Increased and degranulated mast cells in the mucosa, leucocyte infiltration in the lamina propria, vacuole formation in the urothelial cells, loose tight junction, dilated intercellular spaces and altered proliferative activity were observed in the stress group when compared with the control. The increase in the number of mast cells and especially degranulated mast cells and vacuole formation and the loose tight junction of the urothelium correlated with the histopathological findings of interstitial cystitis.

The extracellular matrix of rat pacinian corpuscles: an analysis of its fine structure

The Pacinian corpuscle consists of a sensory axon terminal that is enveloped by two different structures, the inner core and the capsule. Since proteoglycans are extremely water soluble and are extracted by conventional methods for electron microscopy, the current picture of the structural composition of the extracellular matrix in the inner core and the capsule of the Pacinian corpuscle is incomplete. To study the structural composition of the extracellular matrix of the Pacinian corpuscles, cationic dyes (ruthenium red, alcian blue, acridine orange) and tannic acid were applied simultaneously with the aldehyde fixation. The interosseal Pacinian corpuscles of the rat were fixed either in 2% formaldehyde and 1.5% glutaraldehyde, with the addition of one of these cationic dyes or, in Zamboni's fixative, with tannic acid added. The cationic dyes and tannic acid revealed a different structural pattern of proteoglycans in the extracellular matrix in the inner core and in the capsule of the rat Pacinian corpuscles. The inner core surrounding the sensory axon terminal is a compartment containing proteoglycans that were distributed not only in the extracellular matrix but also in the cytoplasm of the lamellae. In addition, this excitable domain was separated from the capsular fluid by a thick layer of proteoglycans on its surface. An enlarged interlamellar space of the capsule contained large amounts of proteoglycans that were removed by digestion with chondroitinase-ABC. Ruthenium red and alcian blue provided only electron dense granules, probably corresponding to collapsed monomeric proteoglycan molecules. Acridine orange and tannic acid preserved proteoglycans very well and made it possible to visualize them as "bottlebrush" structures in the electron microscope. These results show that the inner core and the capsule of rat Pacinian corpuscles have different structural patterns of proteoglycans, which are probably involved in different functions.

On the characterisation of the mechanism underlying passive activation of the Ca2+ release-activated Ca2+ current ICRAC in rat basophilic leukaemia cells

1. Tight-seal whole-cell patch clamp experiments were performed to investigate the mechanism whereby passive depletion of stores activates the Ca2+ release-activated Ca2+ current (ICRAC) in rat basophilic leukaemia (RBL) cells. 2. Passive depletion of stores was achieved by dialysing cells with different concentrations of Ca2+ chelators. Low concentrations generally evoked a submaximal ICRAC, which developed slowly and monophasically. Higher concentrations resulted in a biphasic current in which the initial slow monophasic component developed into a faster and bigger second phase. 3. The kinetics of ICRAC as well as its final amplitude were not affected by Ca2+ chelators that had different affinities or speeds of binding. 4. Exogenous Ca2+ binding ratios > or = 16,670 were necessary to fully activate ICRAC. Because the Ca2+ binding ratio within the stores is presumably low, this indicates that other factors like Ca2+ transport across the stores membrane are rate limiting for passive store depletion. 5. Heparin and Ruthenium Red both failed to affect passive Ca2+ leak from the intracellular stores. 6. Treatment with sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump blockers dramatically altered the kinetics of activation of biphasic currents, and increased the amplitude of monophasic ones. 7. Our results suggest that SERCA pumps are very effective in preventing ICRAC from activating passively, and are responsible for the phasic nature of the current, its time course of development and its overall extent.

Species dependence of mitochondrial calcium transients during excitation-contraction coupling in isolated cardiomyocytes

Whether mitochondrial Ca(2+) transport is rapid enough to respond to changes in cytosolic [Ca(2+)] ([Ca(2+)](c)) which occur during excitation-contraction coupling in the heart is controversial; different results wereobtained with different techniques and different species. In this study mitochondrial [Ca(2+)] ([Ca(2+)](m)) was measured in indo-1/AM-loaded myocytes from rat and guinea-pig hearts where the cytosolic indo-1 had been removed by extended incubation of cells at 37 degrees C ("heat treatment"). The mitochondrial origin of the remaining fluorescence was confirmed by sensitivity of the indo-1 signal to ruthenium red. In resting rat myocytes, [Ca(2+)](m) was lower than [Ca(2+)](c), whereas in guinea-pig cells [Ca(2+)](m) was higher than [Ca(2+)](c). Upon electrical stimulation of cells, no change occurred in [Ca(2+)](m) in rat myocytes. However, in guinea-pig cells mitochondrial Ca(2+) transients were clearly visible with a mean indo-1 ratio amplitude of 0.153 +/- 0.2 (n = 20), compared with 0.306 +/- 0.02 (n = 25), p < 0.001, prior to heat treatment. These observations suggest significant differences in mitochondrial Ca(2+) transport in cardiomyocytes from different species.

Differential utilization of cyclic ADP-ribose pathway by chemokines to induce the mobilization of intracellular calcium in NK cells

We show here that cyclic adenosine diphosphate-ribose (cADPR) may be a second messenger for chemokines. Extracts collected from NK cells stimulated with IL-8 for 2 min were incubated with beta-NAD for an additional 2 min (designated as IL-8 extracts). This mixture elevated the mobilization of (Ca(2+))(i) in alpha-toxin permeabilized NK cells. This activity was inhibited upon prior incubation of these cells with ruthenium red but not with heparin. Purified cADPR and not Ins 1,4,5 P(3) desensitized NK cells to the calcium mobilization effect of IL-8 extracts. Further analysis showed that ruthenium red and heparin differentially inhibit RANTES-, SDF-1alpha-, or MDC-induced calcium mobilization in IL-2-activated NK cells. Also, introduction of anti-ryanodine receptor antibody inside streptolysin O-permeabilized NK cells resulted in complete inhibition of MDC, and only partial inhibition of RANTES and SDF-1alpha-induced calcium fluxes in NK cells. Collectively, these results suggest that chemokines may utilize the cADPR/ryanodine receptor pathway as well as the Ins 1,4,5 P(3)/Ins 1,4,5 P(3) receptor signaling pathway to induce the accumulation of calcium in NK cells.

Use of Ca2+ modulation to evaluate biliary excretion in sandwich-cultured rat hepatocytes

Previous work in our laboratory has indicated that biliary excretion of a substrate in sandwich-cultured hepatocytes can be quantitated by measurement of substrate accumulation in the presence and absence of extracellular Ca2+. The present study was designed to examine the effects of Ca2+ on taurocholate accumulation and tight junction integrity in cultured hepatocytes. Kinetic modeling was used to characterize taurocholate disposition in the hepatocyte monolayers in the presence and absence of extracellular Ca2+. The accumulation of taurocholate in freshly isolated hepatocytes, which lack an intact canalicular network, was the same in the presence and absence of extracellular Ca2+. Electron microscopy studies showed that Ca2+ depletion increased the permeability of the tight junctions to ruthenium red, demonstrating that tight junctions were the major diffusional barrier between the canalicular lumen and the extracellular space. Cell morphology and substrate accumulation studies in the monolayers indicated that Ca2+ depletion disrupted the tight junctions in 1 to 2 min. The integrity of the disrupted tight junctions was not re-established completely after reincubation in the presence of Ca2+ for 1 h. The accumulation of taurocholate was described best by a two-compartment model (cytosol and bile) with Michaelis-Menten kinetics for both uptake and biliary excretion. In summary, Ca2+ depletion does not alter hepatocyte transport properties of taurocholate. Ca2+ modulation may be a useful approach to study biliary excretion of substrates in sandwich-cultured hepatocytes.

Clearance of large Ca2+ loads in a single smooth muscle cell: examination of the role of mitochondrial Ca2+ uptake and intracellular pH

Redistribution of cytosolic free Ca2+ following Ca2+ influx into the cytoplasm was studied in single smooth muscle cells isolated from guinea-pig urinary bladder. Voltage-clamped cells were loaded with a low-affinity fluorophore Indo-1FF. A decay of free intracellular Ca2+ ([Ca2+]i) after the termination of the depolarizing pulse (1 s from -50 mV to +20 mV) was fitted with a single exponential and the effect of various substances on the time constant was compared. At a holding potential of +80 mV the [Ca2+]i decay was 1.56 times slower compared to that at -50 mV suggesting the presence of a voltage-dependent process redistributing Ca2+. In the presence of cyclopiazonic acid (CPA, 10 microM), an inhibitor of sarco(endo)plasmatic Ca2+ pump (SERCa), the [Ca2+]i decay was 3.93 times slower than that in the absence of the inhibitor. Introduction of a polycation Ruthenium Red (RR) (20 microM), an inhibitor of the mitochondrial Ca2+ uniporter, into a cell or collapsing a transmitochondrial H+ gradient with the protonophore CCCP (2 microM) slowed down the [Ca2+]i decay 6.05-fold and 9.78-fold, respectively. The apparent amplitude of [Ca2+]i increments was also increased by CCCP. Increasing H+ buffering power in the intracellular solution from 10 mM to 40 mM of HEPES greatly reduced the effect of CCCP on [Ca2+]i decay. A further increase in HEPES concentration to 100 mM eliminated the effects of CCCP both on the time course of [Ca2+]i decay and on the amplitude of [Ca2+]i increment. Perfusion of RR together with 100 mM HEPES into the cytoplasm was without effect on the decay time course of [Ca2+]i. The effect of CPA on [Ca2+]i decay was also reduced in cells loaded with 100 mM HEPES; the time constant in the presence of CPA was slowed down by a factor of 2.18. Application of 10 mM Na(+)-butyrate to the cells loaded with 10 mM HEPES resulted in a slowing down of [Ca2+]i decay: the time constant was increased by a factor of 5.84. Measurement of intracellular pH with SNARF-1 confirmed cytoplasmic acidification during application of Na(+)-butyrate and CCCP. It is concluded that the contribution of mitochondrial Ca2+ uptake to the rapid [Ca2+]i decay is much less than could be extrapolated from action of protonophores in these smooth muscle cells. The results also demonstrate the importance of intracellular pH for Ca2+ handling in the cytoplasm of smooth muscle cells.

[Capsule formation in Pasteurella multocida, serovar A]

In this work the process of capsule formation in P.multocida bovine strain, serovar A, has been studied. The cultures were grown on liquid and solid nutrient media prepared on the basis of Hottinger hydrolysate and synthetic culture medium 199. Extracellular material was detected by the method electron cytochemistry with ruthenium red and polycationic ferritin. As revealed by specific staining and labeling, P.multocida capsule of serovar A was found to contain material of the polysaccharide nature. But the capsular structures of obtained from agar-grown and broth cultures were different. The capsular layer on the surface of cells grown in Hottinger's broth was found to be more pronounced.

Ratiometric confocal Ca2+ measurements with visible wavelength indicators in d-amphetamine-treated central snail neuron

1. The bursting firing of action potentials and cytosolic calcium content in d-amphetamine-treated RP4 neurons of the African snail, Achatina fulica Ferussac, were studied elelctrophysiologically and optopharmacologically. 2. d-Amphetamine elicited bursting of firing of action potentials in central RP4 neuron. The bursting firing of action potentials was blocked following extracellular application of ruthenium red, the calcium uptake and release inhibitor from mitochondria. 3. At the same neuron, image analysis using ratiometric measurement on calcium green 1 and Texas red dextran (70,000 MW) with laser-scanning confocal microscopy revealed that cytosolic calcium content was increased after d-amphetamine treatment. 4. Our results support the view that the bursting firing of action potentials elicited by d-amphetamine is associated with cytosolic calcium content.

Polyamine modulation of mitochondrial calcium transport. I. Stimulatory and inhibitory effects of aliphatic polyamines, aminoglucosides and other polyamine analogues on mitochondrial calcium uptake

In this study, the regulation of mitochondrial Ca2+ transport by polyamines structurally related to spermine and by analogous polycationic compounds was characterized. Similar to spermine, a number of amino groups containing cationic compounds exerted a dual effect on Ca2+ transport of isolated rat liver mitochondria: a decrease in Ca2+ uptake velocity and an enhancement of Ca2+ accumulation. In contrast to the effects of spermine and other aliphatic polyamines, however, the accumulation-enhancing effect of aminoglucosides, basic polypeptides, and metal-amine complexes turned into an inhibition of Ca2+ accumulation at higher concentrations. Within groups of structurally related compounds, the potency to decrease Ca2+ uptake velocity and to enhance Ca2+ accumulation correlated with the number of cationic charges. The presence of multiple, distributed cationic charges was a necessary, but not sufficient criterion for effects on mitochondrial Ca2+ transport, because cationic polyamines and basic oligopeptides which did not enhance mitochondrial Ca2+ accumulation could be identified. Spermine was not able to antagonize the blocking of Ca2+ uptake by ruthenium red, but rather showed an apparent synergism, which can be explained as a displacement of membrane-bound Ca2+ by spermine. The aminoglucosides, gentamicin and neomycin, but not the inactive polyamine bis(hexamethylene)-triamine, inhibited the binding of spermine to intact mitochondria. Apparently, the binding of spermine, gentamicin, and a number of polyamine analogues to low-affinity binding sites at mitochondria, which have low, but distinct structural requirements and which may correspond to phospholipid headgroups, indirectly influences the activity state of the mitochondrial Ca2+ uniporter. The ability of aminoglucosides to displace spermine from the mitochondria and to inhibit mitochondrial Ca2+ accumulation may contribute to the mitochondrial lesions, which are known to occur early in the course of aminoglucoside-induced nephrotoxicity.