Macrophages possess probenecid-inhibitable organic anion transporters that remove fluorescent dyes from the cytoplasmic matrix

A proprioceptive role for an exteroceptive mechanoafferent neuron in Aplysia

Afferent regulation of centrally generated activity is likely to be more complex than has been established. We show that a neuron that is an exteroceptor can also function as a proprioceptor. We study the Aplysia neuron B21. Previous data suggest that B21 functions as an exteroceptor during the radula closing/retraction phase of ingestive feeding. We show that the tissue innervated by B21, the subradula tissue (SRT), is innervated by a motor neuron (B66) and that B66-induced SRT contractions trigger centripetal spikes in B21. Thus, B21 is also a proprioceptor. To determine whether exteroceptive and proprioceptive activities occur during the same phase of ingestive feeding, we further characterize B66. We show that B66 stimulation does not close or retract the radula. Instead it opens it. Moreover, B66 is electrically coupled to other opening/protraction neurons. Finally, we elicit motor programs in semi-intact preparations and show that during radula opening/protraction we observe B66 activity, SRT contractions, and spikes in B21 that can be eliminated if B66 is indirectly hyperpolarized. B21 is, therefore, likely to act as an exteroceptor during one phase of ingestive feeding and as a proprioceptor during the antagonistic phase. Previous experiments have shown that centripetal spikes in B21 are only transmitted to one follower if they are "gated in" by depolarization. During ingestive programs B21 is centrally depolarized during closing/retraction, but it is not depolarized during opening/protraction. We sought to determine whether there are other followers that receive B21 input when it is not centrally depolarized. We found one such cell. Moreover, we found that stimulation of B21 during radula opening/protraction significantly decreases the duration of this phase of behavior. Thus, proprioceptive activity in B21 is likely to have an impact on motor programs.

Diverse synaptic connections between peptidergic radula mechanoafferent neurons and neurons in the feeding system of Aplysia

The buccal ganglion of Aplysia contains a heterogeneous population of peptidergic, radula mechanoafferent (RM) neurons. To investigate their function, two of the larger RM cells (B21, B22) were identified by morphological and electrophysiological criteria. Both are low-threshold, rapidly adapting, mechanoafferent neurons that responded to touch of the radula, the structure that grasps food during ingestive and egestive feeding movements. Sensory responses of the cells consisted of spike bursts at frequencies of 8-35 Hz. Each cell was found to make chemical, electrical, or combined synapses with other sensory neurons, motor neurons and interneurons involved in radula closure and/or protraction-retraction movements of the odontophore. Motor neurons receiving input included the following: B8a/b, B15, and B16, which innervate muscles contributing to radula closing; and B82, a newly identified neuron that innervates the anterodorsal region of the I1/I3 muscles of the buccal mass. B21 and B22 can affect buccal motor programs by way of their connections to interneurons such as B19 and B64. Fast, chemical, excitatory postsynaptic potentials (EPSPs) produced by RM neurons, such as B21, exhibited strong, frequency-dependent facilitation, a form of homosynaptic plasticity. Firing B21 also produced a slow EPSP in B15 that increased the excitability of the cell. Thus a sensory neuron mediating a behavioral response may have modulatory effects. The data suggest multiple functions for RM neurons including 1) triggering of phase transitions in rhythmic motor programs, 2) adjusting the force of radula closure, 3) switching from biting to swallowing or swallowing to rejection, and 4) enhancing food-induced arousal.

Measurement of intracellular calcium

To a certain extent, all cellular, physiological, and pathological phenomena that occur in cells are accompanied by ionic changes. The development of techniques allowing the measurement of such ion activities has contributed substantially to our understanding of normal and abnormal cellular function. Digital video microscopy, confocal laser scanning microscopy, and more recently multiphoton microscopy have allowed the precise spatial analysis of intracellular ion activity at the subcellular level in addition to measurement of its concentration. It is well known that Ca2+ regulates numerous physiological cellular phenomena as a second messenger as well as triggering pathological events such as cell injury and death. A number of methods have been developed to measure intracellular Ca2+. In this review, we summarize the advantages and pitfalls of a variety of Ca2+ indicators used in both optical and nonoptical techniques employed for measuring intracellular Ca2+ concentration.

Parasitophorous vacuoles of Leishmania mexicana acquire macromolecules from the host cell cytosol via two independent routes

The intracellular parasite Leishmania survives and proliferates in host macrophages. In this study we show that parasitophorous vacuoles of L. mexicana gain access to cytosolic material via two different routes. (1) Small anionic molecules such as Lucifer Yellow are rapidly transported into the vacuoles by an active transport mechanism that is sensitive to inhibitors of the host cell's organic anion transporter. (2) Larger molecules such as fluorescent dextrans introduced into the host cell cytosol are also delivered to parasitophorous vacuoles. This transport is slower and sensitive to modulators of autophagy. Infected macrophages were examined by two novel assays to visualize and quantify this process. Immunoelectron microscopy of cells loaded with digoxigenin-dextran revealed label in multivesicular endosomes, which appeared to fuse with parasitophorous vacuoles. The inner membranes of the multivesicular vesicles label strongly with antibodies against lysobisphosphatidic acid, suggesting that they represent a point of confluence between the endosomal and autophagosomal pathways. Although the rate of autophagous transfer was comparable in infected and uninfected cells, infected cells retained hydrolyzed cysteine proteinase substrate to a greater degree. These data suggest that L. mexicana-containing vacuoles have access to potential nutrients in the host cell cytosol via at least two independent mechanisms.

A pair of reciprocally inhibitory histaminergic sensory neurons are activated within the same phase of ingestive motor programs in Aplysia

Previous studies have shown that each buccal ganglion in Aplysia contains two B52 neurons, one in each hemiganglion. We now show that there are two B52 neurons in a single buccal hemiganglion and four cells in an animal. We also show that the B52 neurons are histamine-immunoreactive and use reverse phase HPLC to show that the histamine-immunoreactive substance is authentic histamine. Previous studies have shown that the B52 neurons make numerous inhibitory synaptic connections with neurons active during the radula closing/retraction phase of ingestive motor programs. A computational model of the Aplysia feeding central pattern generator has, therefore, suggested that the B52 neurons play a role in terminating closing/retraction. Consistent with this idea we show that both B52 neurons fire at the beginning of radula opening/protraction. We also show that both B52 neurons are sensory neurons. They are depolarized when a flap of connective tissue adjacent to the buccal commissural arch is stretched. During ingestive feeding this is likely to occur at the peak of closing/retraction as opening/protraction begins. In the course of this study we compare the two ipsilateral B52 neurons and show that these cells are virtually indistinguishable; e.g., they use a common neurotransmitter, make the same synaptic connections, and are both sensory as well as premotor neurons. Nevertheless we show that the B52 neurons are reciprocally inhibitory. Our results, therefore, strikingly confirm theoretical predictions made by others that neurons that inhibit each other will not necessarily participate in antagonistic phases of behavior.

Actions of a pair of identified cerebral-buccal interneurons (CBI-8/9) in Aplysia that contain the peptide myomodulin

A combination of biocytin back-fills of the cerebral-buccal connectives and immunocytochemistry of the cerebral ganglion demonstrated that of the 13 bilateral pairs of cerebral-buccal interneurons in the cerebral ganglion, a subpopulation of 3 are immunopositive for the peptide myomodulin. The present paper describes the properties of two of these cells, which we have termed CBI-8 and CBI-9. CBI-8 and CBI-9 were found to be dye coupled and electrically coupled. The cells have virtually identical properties, and consequently we consider them to be "twin" pairs and refer to them as CBI-8/9. CBI-8/9 were identified by electrophysiological criteria and then labeled with dye. Labeled cells were found to be immunopositive for myomodulin, and, using high pressure liquid chromatography, the cells were shown to contain authentic myomodulin. CBI-8/9 were found to receive synaptic input after mechanical stimulation of the tentacles. They also received excitatory input from C-PR, a neuron involved in neck lengthening, and received a slow inhibitory input from CC5, a cell involved in neck shortening, suggesting that CBI-8/9 may be active during forward movements of the head or buccal mass. Firing of CBI-8 or CBI-9 resulted in the activation of a relatively small number of buccal neurons as evidenced by extracellular recordings from buccal nerves. Firing also produced local movements of the buccal mass, in particular a strong contraction of the I7 muscle, which mediates radula opening. CBI-8/9 were found to produce a slow depolarization and rhythmic activity of B48, the motor neuron for the I7 muscle. The data provide continuing evidence that the small population of cerebral buccal interneurons is composed of neurons that are highly diverse in their functional roles. CBI-8/9 may function as a type of premotor neuron, or perhaps as a peptidergic modulatory neuron, the functions of which are dependent on the coactivity of other neurons.

C-PR neuron of Aplysia has differential effects on "Feeding" cerebral interneurons, including myomodulin-positive CBI-12

Head lifting and other aspects of the appetitive central motive state that precedes consummatory feeding movements in Aplysia is promoted by excitation of the C-PR neuron. Food stimuli activate C-PR as well as a small population of cerebral-buccal interneurons (CBIs). We wished to determine if firing of C-PR produced differential effects on the various CBIs or perhaps affected all the CBIs uniformly as might be expected for a neuron involved in producing a broad undifferentiated arousal state. We found that when C-PR was fired, it produced a wide variety of effects on various CBIs. Firing of C-PR evoked excitatory input to a newly identified CBI (CBI-12) the soma of which is located in the M cluster near the previously identified CBI-2. CBI-12 shares certain properties with CBI-2, including a similar morphology and a capacity to drive rhythmic activity of the buccal-ganglion. Unlike CBI-2, CBI-12 exhibits myomodulin immunoreactivity. Furthermore when C-PR is fired, CBI-12 receives a polysynaptic voltage-dependent slow excitation, whereas, CBI-2 receives relatively little input. C-PR also polysynaptically excites other CBIs including CBI-1 and CBI-8/9 but produces inhibition in CBI-3. In addition, firing of C-PR inhibits plateau potentials in CBI-5/6. The data suggest that activity of C-PR may promote the activity of one subset of cerebral-buccal interneurons, perhaps those involved in ingestive behaviors that occur during the head-up posture. C-PR also inhibits some cerebral-buccal interneurons that may be involved in behaviors in which C-PR activity is not required or may even interfere with other feeding behaviors such as rejection or grazing, that occur with the head down.

A pair of reciprocally inhibitory histaminergic sensory neurons are activated within the same phase of ingestive motor programs in Aplysia

Previous studies have shown that each buccal ganglion in Aplysia contains two B52 neurons, one in each hemiganglion. We now show that there are two B52 neurons in a single buccal hemiganglion and four cells in an animal. We also show that the B52 neurons are histamine-immunoreactive and use reverse phase HPLC to show that the histamine-immunoreactive substance is authentic histamine. Previous studies have shown that the B52 neurons make numerous inhibitory synaptic connections with neurons active during the radula closing/retraction phase of ingestive motor programs. A computational model of the Aplysia feeding central pattern generator has, therefore, suggested that the B52 neurons play a role in terminating closing/retraction. Consistent with this idea we show that both B52 neurons fire at the beginning of radula opening/protraction. We also show that both B52 neurons are sensory neurons. They are depolarized when a flap of connective tissue adjacent to the buccal commissural arch is stretched. During ingestive feeding this is likely to occur at the peak of closing/retraction as opening/protraction begins. In the course of this study we compare the two ipsilateral B52 neurons and show that these cells are virtually indistinguishable; e.g., they use a common neurotransmitter, make the same synaptic connections, and are both sensory as well as premotor neurons. Nevertheless we show that the B52 neurons are reciprocally inhibitory. Our results, therefore, strikingly confirm theoretical predictions made by others that neurons that inhibit each other will not necessarily participate in antagonistic phases of behavior.

Proprioceptive input to feeding motor programs in Aplysia

Although central pattern generators (CPGs) can produce rhythmic activity in isolation, it is now generally accepted that under physiological conditions information from the external and internal environment is incorporated into CPG-induced motor programs. Experimentally advantageous invertebrate preparations may be particularly useful for studies that seek to characterize the cellular mechanisms that make this possible. In these experiments, we study sensorimotor integration in the feeding circuitry of the mollusc Aplysia. We show that a premotor neuron with plateau properties, B51, is important for generating the radula closing/retraction phase of ingestive motor programs. When B51 is depolarized in semi-intact preparations, radula closing/retractions are enhanced. When B51 is hyperpolarized, radula closing/retractions are reduced in size. In addition to being important as a premotor interneuron, B51 is also a sensory neuron that is activated when the feeding apparatus, the radula, rotates backward. The number of centripetal spikes in B51 is increased if the resistance to backward rotation is increased. Thus, B51 is a proprioceptor that is likely to be part of a feedback loop that insures that food will be moved into the buccal cavity when difficulty is encountered. Our data suggest, therefore, that Aplysia are able to adjust feeding motor programs to accommodate the specific qualities of the food ingested because at least one of the neurons that generates the basic ingestive motor program also serves as an on-line monitor of the success of radula movements.

Proprioceptive input to feeding motor programs in Aplysia

Although central pattern generators (CPGs) can produce rhythmic activity in isolation, it is now generally accepted that under physiological conditions information from the external and internal environment is incorporated into CPG-induced motor programs. Experimentally advantageous invertebrate preparations may be particularly useful for studies that seek to characterize the cellular mechanisms that make this possible. In these experiments, we study sensorimotor integration in the feeding circuitry of the mollusc Aplysia. We show that a premotor neuron with plateau properties, B51, is important for generating the radula closing/retraction phase of ingestive motor programs. When B51 is depolarized in semi-intact preparations, radula closing/retractions are enhanced. When B51 is hyperpolarized, radula closing/retractions are reduced in size. In addition to being important as a premotor interneuron, B51 is also a sensory neuron that is activated when the feeding apparatus, the radula, rotates backward. The number of centripetal spikes in B51 is increased if the resistance to backward rotation is increased. Thus, B51 is a proprioceptor that is likely to be part of a feedback loop that insures that food will be moved into the buccal cavity when difficulty is encountered. Our data suggest, therefore, that Aplysia are able to adjust feeding motor programs to accommodate the specific qualities of the food ingested because at least one of the neurons that generates the basic ingestive motor program also serves as an on-line monitor of the success of radula movements.

Uptake of HgCl2 and MeHgCl in an insect cell line (Aedes albopictus C6/36)

We studied the uptake mechanism of mercuric chloride (Hg) and methylmercuric chloride (MeHg) in Aedes albopictus C6/36 cells. The uptake kinetics, together with the effect of temperature and a metabolic inhibitor (2, 4-dinitrophenol) on the mercury accumulation, were examined. Both amounts of internalized Hg and MeHg increased linearly with the extracellular concentration. Initially, the influx rate was high for both metal species but MeHg was found to accumulate seven times faster than Hg. At longer exposure times it leveled off for Hg, while for MeHg, the intracellular concentration decreased. Hg toxicity was not significantly influenced by elevated temperatures; in contrast there was a marked decrease of the LC50/24h value for MeHg. On the other hand, Hg accumulation was temperature dependent but MeHg was not. The different toxicity and uptake rate of both mercury compounds can be explained in terms of membrane permeability and target site. For Hg the main target seems to be the plasma membrane, while MeHg readily crosses this barrier and reacts with intracellular targets. 2, 4-Dinitrophenol had no effect on the accumulation of Hg but that of MeHg was doubled. This increased MeHg accumulation might be the result of the inhibition of an active MeHg efflux mechanism; this is in agreement with the MeHg influx kinetics. Despite these differences between Hg and MeHg, which probably result from their physicochemical properties, our experiments indicate that, for both mercury species, simple diffusion is probably the main way to entrance in Aedes cells.

Noise-induced transient microlesions in the cell membranes of auditory hair cells

Several types of nonauditory cells recover from transitory mechanically induced microlesions in their cell membranes. We report evidence that hair cells in the auditory papilla of the alligator lizard suffered similar membrane wounding when exposed to noise loud enough to induce a temporary threshold shift. Lucifer yellow, a molecular marker that does not normally penetrate through the cell membrane into the cytoplasm, was introduced into the extracellular fluid bathing the basolateral membrane of the hair cells. We assessed the effect of loud noise on the function of the ear by measuring compound action potentials of the auditory nerve before exposure to the noise, immediately after cessation of the noise, and after recovering overnight. Hair cells that were exposed to the noise took up much more Lucifer yellow than hair cells that were not exposed. We propose that the Lucifer yellow entered the hair cells via noise-induced lesions in their cell membranes, and that the cells were able to survive and recover functionally.

Transport of lucifer yellow CH into plant vacuoles--evidence for direct energization of a sulphonated substance and implications for the design of new molecular probes

Contrasting observations exist which indicate that in plants the fluorescent dye lucifer yellow CH (LYCH) either can be used as a tracer for endocytosis or as a substrate for an anion transporter located at the vacuolar membrane. In addition, LYCH as a disulphonated substance may represent an analogue of sulphonated or sulfated natural compounds like some flavonoids. We performed uptake experiments with LYCH into isolated rye vacuoles and observed saturable (Km = 0.3-0.6 mM) vacuolar transport and accumulation of the dye against the concentration gradient only when MgATP was present. GTP and, to a low extent, UTP could substitute for ATP, while the non-hydrolysable ATP analogue AMP-PNP did not drive LYCH uptake. Vanadate and probenecid, the latter substance is known to inhibit organic anion transport at the liver canalicular membrane, both strongly decreased the vacuolar uptake of LYCH, while bafilomycin A1, a specific inhibitor of the vacuolar H+-ATPase, had no effect. Together with the fact that abolishment of the delta pH via CCCP had only a weak influence on LYCH accumulation, our results indicate that this compound is taken up into rye vacuoles by a directly energized process. Uptake of LYCH was strongly inhibited by other sulfated compounds including sulfobromophthalein and the flavones apigenin 7,4'-disulfate and luteolin 7,4'-disulfate arguing for the presence of a vacuolar transporter for structurally different sulphonated or sulfated compounds. Glucuronates like the rye-specific flavone luteolin 7-O-diglucuronide also strongly decreased uptake of the dye, whereas only a weak effect was observed in the presence of glutathione and a glutathione conjugate, suggesting that LYCH uptake is not mediated via the vacuolar glutathione conjugate pump.

Effects of intracellular Ca2+ chelating on noradrenaline release in normoxic and anoxic hearts

1. Ischaemia and anoxia induce excessive noradrenaline (NA) release in the heart by a mechanism independent of both nerve activity and extracellular Ca2+. The present study was designed to examine the potential role of intracellular Ca2+ mobilization in anoxic NA release in the heart by chelating intracellular free Ca2+. 2. In normoxic hearts, preloading with an intracellular free Ca2+ chelator (BAPTA) reduced neuronal NA release by 65%, confirming the effectiveness of the loading protocol. Release of NA independent of nerve activity occurred in hearts subjected to a 40 min period of anoxic, substrate-free and nominal Ca(2+)-free perfusion. Loading hearts with BAPTA prior to anoxia failed to reduce NA overflow (1561 +/- 147 vs 1496 +/- 206 pmol/g over 40 min). Infusion with BAPTA (20 mumol/L) during the first 25 min of the anoxic period reduced the quantity of anoxic NA release by approximately 25% from 2013 +/- 124 to 1476 +/- 207 pmol/g (P < 0.05). 3. Our results confirm that anoxic NA release is predominantly a Ca(2+)-independent process with Ca2+ mobilization from endogenous storage playing only a minor contributing role.

Cellular retention of liposome-delivered anionic compounds modulated by a probenecid-sensitive anion transporter

PURPOSE

Drug carriers such as liposomes may enhance the intracellular delivery of therapeutic agents for infectious or neoplastic diseases. However, the mechanisms affecting cellular retention of liposome contents are understood poorly. We tested the hypothesis that retention of anionic compounds may be modulated by a nonspecific probenecid-sensitive anion transport mechanism, and that liposome composition may determine the impact of such transporters on drug retention by cells.

METHODS

The fluorescent anionic dye hydroxy-pyrene-[1,3,6]-trisulfonate (HPTS) was transferred to the cytoplasm of cultured CV-1 or J774 cells by direct needle-microinjection or by ATP-induced permeabilization of the-plasma membrane, respectively, to investigate whether the cells have anion transport mechanisms capable of extruding HPTS from the cytoplasm. Cellular retention of dye was monitored in the presence and absence of the anion transport inhibitors probenecid or sulfinpyrazone. Liposomes containing HPTS were co-labeled with tetramethylrhodamine-labeled phosphatidylethanolamine (Rho-PE) as a marker of liposome membrane fate, and uptake was investigated using J774 cells.

RESULTS

Needle-injected HPTS underwent both sequestration in early endocytic vesicles and rapid extrusion into the extracellular medium. Probenecid or sulfinpyrazone reduced the extrusion of HPTS. Thus HPTS is a substrate for a probenecid-sensitive anion transporter in J774 and CV1 cells. After delivery via fluid liposomes composed of phosphatidylglycerol:phosphatidylcholine:cholesterol (3:7:5 mole ratio) and co-labeled with Rho-PE, cell-associated HPTS declined more rapidly than did Rho-PE. Exposure of cells to 5 mM probenecid doubled the quantity of HPTS retained by cells, without changing the retention of the Rho-PE membrane marker. In contrast, the effect of probenecid was negligible when gel-phase liposomes of distearoylphosphatidylglycerol:cholesterol (10:5 mole ratio) were used.

CONCLUSIONS

Probenecid-sensitive nonspecific anion transporters can mediate the extrusion of model anions delivered via liposomes. However, liposome composition modulates the amount of material subject to extrusion from cells, possibly by altering the endocytic compartment in which liposomes release their contents.

Effects of buffering intracellular free calcium on neutrophil migration through three-dimensional matrices

Repeated transient increases in intracellular free calcium levels ([Ca2-]i) are required for polymorphonuclear neutrophil migration on two-dimensional surfaces coated with fibronectin or vitronectin. Cells in which [Ca2+]i is buffered with quin2 become stuck on these substrates. Neutrophils migrating through the extracellular matrix in vivo encounter these and other substrates in a three-dimensional architecture that may alter the spatial distribution of adhesion receptors in contact with the matrix. In this study, we used fluorescence confocal microscopy to obtain moving three-dimensional images of neutrophils migrating through a biological tissue (human amnion) in the presence and absence of [Ca2+]i-buffering with quin2. In the absence of buffering, [Ca2+]i transients similar to those seen in cells migrating in two-dimensions were observed. [Ca2+]i-buffered neutrophils were able to migrate into the matrix, but they became attached firmly to the substrate at the rear of the cell, resulting in a drastically elongated morphology. Immunofluorescence revealed that neutrophils adhered to regions of the matrix that contained fibronectin. RGD-containing peptides and antibodies that block integrin adhesion receptors for fibronectin and vitronectin were able to rescue the migration of quin2-treated cells through three-dimensional gels containing fibronectin and vitronectin. These data show that neutrophils migrating through physiologically relevant, three-dimensional matrices undergo repetitive increases in [Ca2+]i that are required for integrin-mediated detachment from the matrix.

Use of a fluorescent probe to assess the activities of candidate agents against intracellular forms of Encephalitozoon microsporidia

Microsporidia are obligate intracellular protozoan parasites. Three species of the genus Encephalitozoon are among the microsporidia that infect immunodeficient humans. These species, Encephalitozoon cuniculi, Encephalitozoon hellem, and Encephalitozoon intestinalis, all develop in a parasitophorous vacuole within a host cell. The present study describes a method that uses the fluorescent probe calcein and confocal microscopy to detect drug-induced effects in Encephalitozoon-infected green monkey kidney cells. The effects were as follows: (i) changes in parasite organization within the parasitophorous vacuole; (ii) swelling and gross morphological changes of parasite developing stages in situ; (iii) killing of developing parasite stages in situ, detected by their uptake of the fluorescent probe; and (iv) reduction in the viability of the host cell population, assessed by the loss of the probe. Verapamil and itraconazole were used to increase the vital dye loading by both uninfected and infected cells. Agents with known antimicrosporidial activity, albendazole and fumagillin, caused all three types of parasite changes at concentrations that had no detectable effect on host cell viability. The effective doses of albendazole and fumagillin that caused swelling and disorganization of parasite developing stages were 5 x 10(-7) and 10(-6) M respectively. Killing of developing stages was detected at 10-fold-higher concentrations for these agents and at 10(-5) M for metronidazole. This method can be used to screen candidate antimicrosporidial agents in infected cultured cells.

The effect of BCECF on intracellular pH of human platelets

2',7'-Bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) is frequently used for fluorometric determination of intracellular pH (pHi) and its metabolic changes. Studies of BCECF-loaded platelets have reported different pHi values in the range of 6.98 to 7.35, despite the use of the same probe. It is now shown that intracellular BCECF (BCECFi) content affects pHi, and that its over-loading, leads to significantly lower pHi. Different pHi values can be reproduced by changing BCECFi, as reflected by fluorescence intensity. The major loading factors are: the concentration of the probe parent compound, BCECF acetoxymethyl ester (AM), and whether this ester is partly hydrolyzed externally when applied in plasma. When least affected by BCECF, platelet pHi is 7.34. High BCECFi does not affect ATP content, buffer capacity, activation of Na+/H+ exchange by protein kinase C (PKC) and basal PKC activity. On the other hand high BCECFi does inhibit the Na+/H+ exchange rate by over 50%. Since the Na+/H+ exchange strongly affects platelets pHi, it is proposed that this inhibition accounts, at least partly, for the lowered pHi in BCECF over-loaded platelets.

A pair of identified interneurons in Aplysia that are involved in multiple behaviors are necessary and sufficient for the arterial-shortening component of a local withdrawal reflex

A bilateral pair of cerebral interneurons, called CC5, contribute to the generation of a number of different behaviors involving head movements. Each cell sends its axon to the ipsilateral and contralateral pedal and pleural ganglia. A weak tactile stimulus to the head excites the ipsilateral CC5; a strong stimulus excites both the ipsilateral and contralateral cells. Firing of CC5 produces powerful shortening of the ipsilateral pedal artery (PA) by means of monosynaptic excitation of the pedal artery shortener (PAS) neuron, the single motor neuron for the artery. A weak touch to a tentacle excites the ipsilateral PAS and evokes a local withdrawal response accompanied by shortening of the ipsilateral PA. In vivo recording of the pedal artery nerve (PAn) showed that PAS was activated bilaterally during defensive head withdrawal elicited by a strong stimulus and was activated unilaterally by a weak stimulus. The responses were eliminated by cutting the ipsilateral cerebral-pleural connective (C-PLC). Electrical stimulation of the cerebral-pleural connective provided evidence that all of the excitatory input to PAS via this connective is provided by CC5. A variety of experimental results indicates that during a local withdrawal reflex of the tentacle, CC5 is necessary and sufficient for the unilateral PA-shortening component of the response and therefore functions as a command neuron for a component of the behavior. The data suggest that during defensive head withdrawal, the two CC5 neurons may act conjointly as a two-neuron command system that is necessary and sufficient for the bilateral arterial-shortening component of the behavior.

A pair of identified interneurons in Aplysia that are involved in multiple behaviors are necessary and sufficient for the arterial-shortening component of a local withdrawal reflex

A bilateral pair of cerebral interneurons, called CC5, contribute to the generation of a number of different behaviors involving head movements. Each cell sends its axon to the ipsilateral and contralateral pedal and pleural ganglia. A weak tactile stimulus to the head excites the ipsilateral CC5; a strong stimulus excites both the ipsilateral and contralateral cells. Firing of CC5 produces powerful shortening of the ipsilateral pedal artery (PA) by means of monosynaptic excitation of the pedal artery shortener (PAS) neuron, the single motor neuron for the artery. A weak touch to a tentacle excites the ipsilateral PAS and evokes a local withdrawal response accompanied by shortening of the ipsilateral PA. In vivo recording of the pedal artery nerve (PAn) showed that PAS was activated bilaterally during defensive head withdrawal elicited by a strong stimulus and was activated unilaterally by a weak stimulus. The responses were eliminated by cutting the ipsilateral cerebral-pleural connective (C-PLC). Electrical stimulation of the cerebral-pleural connective provided evidence that all of the excitatory input to PAS via this connective is provided by CC5. A variety of experimental results indicates that during a local withdrawal reflex of the tentacle, CC5 is necessary and sufficient for the unilateral PA-shortening component of the response and therefore functions as a command neuron for a component of the behavior. The data suggest that during defensive head withdrawal, the two CC5 neurons may act conjointly as a two-neuron command system that is necessary and sufficient for the bilateral arterial-shortening component of the behavior.

Regulation of inducible nitric oxide synthase expression by macrophage purinoreceptors and calcium

Macrophage activation is central to the progression of multiple diseases via the release of inflammatory mediators such as cytokines and nitric oxide. Despite the recognized overlap in the regulatory mechanisms involved in mediator production, little formation exists regarding receptor-initiated signaling pathways that coordinately control multiple end points, such as tumor necrosis factor-alpha (TNF-alpha) and nitric oxide production. In this study, the expression of inducible nitric oxide synthase (iNOS) in macrophages is shown to be regulated by calcium and by a purinoreceptor signaling system. The P2Y purinoreceptor partial agonist, 2-methylthio-ATP (2-MeS-ATP), inhibits the expression of iNOS induced by lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma) in primary macrophages. Additionally, 2-MeS-ATP attenuates the expression of iNOS in macrophages isolated from CD-1 mice challenged with LPS, and it inhibits LPS-induced TNF-alpha and interleukin-1 alpha (IL-1 alpha) release, thereby preventing endotoxic death. Thus, purinoreceptors and calcium are likely to be critical for macrophage activation and the production of inflammatory mediators stimulated by LPS.

Phagosome-lysosome fusion is a calcium-independent event in macrophages

Phagosome-lysosome membrane fusion is a highly regulated event that is essential for intracellular killing of microorganisms. Functionally, it represents a form of polarized regulated secretion, which is classically dependent on increases in intracellular ionized calcium ([Ca2+]i). Indeed, increases in [Ca2+]i are essential for phagosome-granule (lysosome) fusion in neutrophils and for lysosomal fusion events that mediate host cell invasion by Trypanosoma cruzi trypomastigotes. Since several intracellular pathogens survive in macrophage phagosomes that do not fuse with lysosomes, we examined the regulation of phagosome-lysosome fusion in macrophages. Macrophages (M phi) were treated with 12.5 microM bis-(2-amino-S-methylphenoxy) ethane-N,N,N',N',-tetraacetic acid tetraacetoxymethyl ester (MAPT/AM), a cell-permeant calcium chelator which reduced resting cytoplasmic [Ca2+]; from 80 nM to < or = 20 nM and completely blocked increases in [Ca2+]i in response to multiple stimuli, even in the presence of extracellular calcium. Subsequently, M phi phagocytosed serum-opsonized zymosan, staphylococci, or Mycobacterium bovis. Microbes were enumerated by 4',6-diamidino-2-phenylindole, dihydrochloride (DAPI) staining, and phagosome-lysosome fusion was scored using both lysosome-associated membrane protein (LAMP-1) as a membrane marker and rhodamine dextran as a content marker for lysosomes. Confirmation of phagosome-lysosome fusion by electron microscopy validated the fluorescence microscopy findings. We found that phagosome-lysosome fusion in M phi occurs noramlly at very low [Ca2+]i (< or = 20 nM). Kinetic analysis showed that in M phi none of the steps leading from particle binding to eventual phagosome-lysosome fusion are regulated by [Ca2+]i in a rate-limiting way. Furthermore, confocal microscopy revealed no difference in the intensity of LAMP-1 immunofluorescence in phagolysosome membranes in calcium-buffered vs. control macrophages. We conclude that neither membrane recognition nor fusion events in the phagosomal pathway in macrophages are dependent on or regulated by calcium.

Lung surfactant protein A (SP-A) activates a phosphoinositide/calcium signaling pathway in alveolar macrophages

Lung surfactant protein A (SP-A), the main protein component of lung surfactant which lines the alveoli, strongly enhances serum-independent phagocytosis of bacteria by rat alveolar macrophages. We tested if the effect of SP-A is due to interaction with the macrophages or to opsonization of the bacteria. In phagocytosis assays with fluorescein isothiocyanate labeled bacteria, SP-A had no opsonic effect on Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, but enhanced phagocytosis by acting only on the macrophages. We characterized this activation mechanism. With single cell measurements of fura-2 loaded cells we demonstrate that SP-A raises the intracellular free calcium ion concentration 6 to 8 seconds after addition. This calcium mobilization is dose-dependent in that increased SP-A concentrations lead to a higher percentage of responding cells. Additionally, SP-A leads to a dose-dependent and transient generation of inositol 1,4.5-trisphosphate. Release of intracellular stored calcium by SP-A is a prerequisite for its stimulatory effect on phagocytosis, since SP-A-induced enhancement of phagocytosis can be impaired by prior addition of thapsigargin, a Ca(2+)-ATPase inhibitor that leads to depletion of intracellular calcium stores. We conclude that SP-A activates a phosphoinositide/calcium signaling pathway in alveolar macrophages leading to enhanced serum-independent phagocytosis of bacteria.

Reduction of intracellular pH by tenidap. Involvement of cellular anion transporters in the pH change

Tenidap [5-chloro-2,3-dihydro-3-(hydroxy-2-thienylmethylene)-2-oxo-1H- indole-1-carboxamide], a novel antirheumatic agent, produces a rapid and sustained intracellular acidification when applied to cells in culture. To investigate the mechanism by which this change in ionic homeostasis is achieved, the acidification activities of structural analogs of tenidap were determined, and the movements of [14C]tenidap into and out of cells were explored. The acidification activity of tenidap was enhanced by lowering extracellular pH, suggesting that the free acid species was required for this process. Consistent with this requirement, a non-acidic analog of tenidap did not produce a change in intracellular pH (pHi). In contrast, multihalogenated derivatives of tenidap produced greater changes in pHi than did tenidap, and one analog produced a transient acidification from which the cell recovered; this recovery, however, was blocked by an inhibitor of the Na+/H+ antiporter. Fibroblasts incubated with [14C]tenidap achieved within 5 min a level of cell-associated drug that remained constant during longer incubations. Simultaneous addition of the electrogenic ionophore valinomycin or the P-glycoprotein inhibitor 4-(3,4-dihydro-6,7-dimethoxy-2(1H)-isoquinolinyl)-N-[2-(3,4-dimethoxyphe nyl) ethyl]-6,7-dimethoxy-2-quinazolinamine (CP-100,356) caused a time- and concentration-dependent increase in the level of cell-associated [14C]tenidap; other agents tested did not promote this enhanced cellular accumulation. [14C]Tenidap accumulated by fibroblasts in the presence of CP-100,356 subsequently was released when these cells were placed in a tenidap- and CP-100,356-free medium. Importantly, several agents that are known to inhibit anion transport processes, including alpha-cyano-beta-(1-phenylindol-3-yl) acrylate, 5-nitro-2(3-phenylpropylamino)-benzoic acid, and meclofenamic acid, inhibited efflux of [14C]tenidap. In contrast, ethacrynic acid and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid did not impair the efflux process. Likewise, tenidap analogs that produced a sustained intracellular acidification blocked the efflux of [14C]tenidap, but non-acidifying species did not. These data suggest that movements of tenidap into and/or out of cells is a facilitated process subject to pharmacological intervention. Together, the structural selectivity of the acidification response and the evidence of facilitated transport suggest that the pHi modulating activity of tenidap is dependent on its unique physicochemical properties. Due to the dependence of these physicochemical properties on environmental and cellular conditions, in vivo expression of the acidification activity is likely to occur only within restricted environments that favor this tenidap-induced process.

Calcium and hydrogen ion concentrations in the parasitophorous vacuoles of epithelial cells infected with the microsporidian Encephalitozoon hellem

Microsporidia of the genus Encephalitozoon undergo merogony and sporogony in a parasitophorous vacuole within the host cell. Cultured green monkey kidney cells infected with Encephalitozoon hellem were loaded with the fluorescent dyes fura-2 or BCECF in order to measure intracellular concentrations of calcium and hydrogen ions respectively. Both the parasitophorous vacuole calcium concentration and pH values resembled those of the host cell cytoplasm in infected cells. Calcein entered the parasitophorous vacuole but not other host cell vacuoles or parasite stages within the parasitophorous vacuole. The lack of a pH or calcium concentration gradient across the parasitophorous vacuole membrane and the permeability of this membrane to a large anion such as calcein suggest that the vacuole membrane surrounding E. hellem resembles that surrounding some other intracellular parasites such as Toxoplasma gondii. A potential role is discussed for the parasitophorous vacuole calcium concentration in germination in situ.

Fluid phase endocytosis by isolated rabbit lacrimal gland acinar cells

It is well known that lacrimal gland acinar cells retrieve secretory vesicle membrane constituents from their apical plasma membranes after stimulated exocytosis of secretory proteins. There have also been indications of a recycling traffic involving the basal-lateral plasma membranes. In an effort to document this traffic, determine how it is regulated, and discern whether it involves more than one intracellular compartment, we studied internalization of the fluid phase marker, Lucifer Yellow, and its relationship to protein release in acinar cells isolated from rabbit lacrimal glands. Loading of intracellular vesicles was apparent with fluoresence microscopy. Stimulation with carbachol increased both the rate of internalization and the intracellular volume equilibrating with extracellular fluid, suggesting the loading of two compartments. A carbachol concentration of 10 microM increased uptake by 80% during 20-min incubations at 37 degrees C. Increasing the carbachol concentration to 1 mM reduced the response by 50%, and it appeared to do so by decreasing the intracellular volume accessible to extracellular fluid, rather than the rate of endocytosis. Carbachol affected protein release differently, increasing it by 50% at 10 microM and 80% at 1 mM. Acceleration of endocytosis by 10 microM carbachol was transient, becoming negligible after 60 min. Vasoactive intestinal peptide (VIP) and isoproterenol increased internalization 35% and 25% respectively; neither reduced uptake at the highest concentrations tested; and only isoproterenol significantly affected protein secretion. Combinations of VIP and carbachol exerted synergistic effects on both fluid phase internalization and protein release. Steady-state uptake at 18 degrees C in the presence of 10 microM carbachol was equal to uptake at 37 degrees C in the absence of carbachol, suggesting a temperature block in the pathway to at least one endocytic compartment. Decreasing the temperature to 18 degrees C eliminated the inhibitory action of excessive carbachol, suggesting that the compartment whose loading was impaired by excessive carbachol was positioned distal to the temperature block. Carbachol accelerated release of marker from preloaded cells, indicating that it stimulated recycling between the plasma membranes and endocytic compartments. This effect was maximal at a concentration of 10 microM and unchanged with increasing concentrations. In accord with the hypothesis that traffic into and out of a certain compartment was particularly dependent on stimulation, a fraction of the marker taken up by optimally stimulated cells at 37 degrees C was retained unless carbachol or VIP was present in the efflux medium.(ABSTRACT TRUNCATED AT 400 WORDS)

Active cell membrane mechanisms involved in the exclusion of Rh 123 allow distinction between normal and tumoral cells

Human cell lines derived from three epithelial carcinomas (CaSki, HeLa, SiHa), one B lymphoma (BL60), one promyelocytic (HL60), one monocytic (U937) leukemia, one chronic myelogenous leukemia (sensitive K562S; multichemoresistant K562R) and normal human skin fibroblasts were compared for their capacity of staining with rhodamine 123 (Rh 123) and their kinetics of dye exclusion. Cells were exposed for 30 min to 10 micrograms/ml of Rh 123 in culture medium; fluorescence intensity was measured by flow cytometry immediately or 1, 2, 3 and 4 h after staining. The highest fluorescence intensity was observed in carcinoma cell lines; there was no incorporation in multichemoresistant K562R cells. Exclusion of Rh 123 was evaluated from 0 to 4 h, both by flow cytometry and by fluorimetry. Fluorescence intensity measured by flow cytometry decreased slightly in carcinoma and leukemia cells and rapidly in fibroblasts. In all cell lines Rh 123 exclusion was inhibited by 40 mumol/L verapamil and 5 mmol/L probenecid. Thus, incorporation and exclusion of Rh 123 allows distinction between normal and tumoral cells; moreover, inhibition of exclusion by verapamil and probenecid favors the involvement of active cell membrane mechanisms in the exclusion process.

Biphasic increase in cytosolic free calcium induced by bradykinin and histamine in cultured tracheal smooth muscle cells: is the sustained phase artifactual?

The effects of bradykinin (BK) and histamine on intracellular Ca2+ ([Ca2+]i) were studied in fura-2-loaded guinea-pig tracheal smooth muscle cells in culture. BK, at 10 nM, and histamine, at 100 microM, induced a rise in [Ca2+]i which was inhibited by the B2 antagonist Hoe 140 and by the H1 antagonist triprolidine, respectively. This rise in [Ca2+]i is biphasic, consisting of a rapid transient phase followed by a sustained phase. The transient phase, induced by either BK or histamine, was strongly inhibited by thapsigargin, a microsomal Ca(2+)-ATPase inhibitor, usually used to deplete certain intracellular Ca(2+)-stores. Ni2+ (4 mM) did not affect the transient phase but abolished the sustained phase when cells were stimulated by BK, further supporting the fact that the transient phase was only dependent on intracellular Ca2+ pools. The sustained phase was partially (for BK) and completely (for histamine) inhibited by 30 microM Mn2+. This effect could be completely reversed by the addition of DTPA, a cell-impermeant chelator of Mn2+, indicating that the Mn2+ exerted its effect extracellularly. The presence of 1 mM probenecid (an inhibitor of a membrane organic anion transporter that extrudes fura-2) drastically inhibited the sustained phase by more than 77% for BK and 88% for histamine. Our results suggest that the effects of BK and histamine on airway smooth muscle cells are mediated via bradykinin B2 receptors and histamine H1 receptors, respectively whose activation allows the rapid transient rise in [Ca2+]i from thapsigargin-sensitive intracellular Ca2+ pools. The sustained phase is proposed to be drastically influenced by an acceleration of fura-2 extrusion during the increase of [Ca2+]i via a probenecid-sensitive mechanism.

Macrophages loaded with doxorubicin by ATP-mediated permeabilization: potential carriers for antitumor therapy

In many cell types extracellular ATP (ATPe) has been shown to cause reversible plasma membrane permeabilization to low molecular weight (< 900 Da) water-soluble compounds. In the present report we have exploited this technique to incorporate the anticancer drug doxorubicin (DXR), molecular mass 543 Da, into the cytoplasm of two mouse cell lines that had previously been shown to express the ATPe-gated pore, J774 macrophages and tumor necrosis factor (TNF)-resistant L929 fibroblasts. Compared to passively loaded cells, ATPe-mediated reversible permeabilization allowed an at least 4-fold increase in DXR intracellular trapping (0.5 pg/cell versus 2 pg/cell). Analysis of the release kinetics at 37 degrees C showed that about 40% of total intracellular DXR was discharged during the first hour from both ATPe-permeabilized and passively loaded cells; about 15% further release was observed upon incubation up to 4 h. DXR release profiles were similar in ATPe-permeabilized and passively loaded cells. ATPe-permeabilized, DXR-loaded (ATPe-DXR) cells strongly inhibited the proliferation of K562 tumor cells. Taken together these results indicate that ATPe-mediated reversible plasma membrane permeabilization can be effectively used to load cells of different histotypes with high concentrations of DXR. This approach could permit to vehicle high doses of anticancer agents by using living cells while reducing systemic toxic effects.

Intracellular concentrations of antibacterial agents and related clinical implications

Intracellular penetration, accumulation and disposition of antibacterial agents is crucial for effective treatment of infections caused by intracellular bacteria. Intracellular concentrations and locations of both antibacterials and bacteria remain poorly understood and further research is needed to establish the importance of these concepts. For example, concepts that have been shown to be important outcome predictors when applied to concentrations of antibacterial agents in the serum include: (i) the effect of the peak antibacterial serum concentration to minimum concentration inhibitory to 90% of organisms (MIC90) for bacteria; (ii) the effect of length of time the serum antibacterial concentration remains above the MIC90 curve; or (iii) the area under the MIC90 curve, but above the serum antibacterial concentration curve. Further research should determine whether or not these concepts have important applications in an intracellular environment. Intracellular pathogens have been increasingly contributing to respiratory infections in the community. Therefore, on the basis of intracellular activity against bacteria causing respiratory infections, macrolides are favoured as the most broad spectrum class of oral antibacterial agents available for the treatment of patients with community-acquired respiratory infections.

The parasitophorous vacuole membrane surrounding intracellular Toxoplasma gondii functions as a molecular sieve

The obligate intracellular protozoan parasite Toxoplasma gondii creates and enters into a unique membrane-bounded cytoplasmic compartment, the parasitophorous vacuole, when invading mammalian host cells. By microinjecting polar fluorescent molecules into individual T. gondii-infected fibroblasts, we show here that the parasitophorous vacuole membrane (PVM) surrounding the parasite functions as a molecular sieve. Lucifer yellow (457 Da) displayed free bidirectional flux across the PVM and distinctly outlined the parasites, which did not take up the dye, within the vacuole. This dye movement was not appreciably delayed by pretreatment of cells with 5 mM probenecid or chilling the monolayer to 5 degrees C, suggesting that dye movement was due to passive permeation through a membrane pore rather than active transport. Calcein, fluo-3, and a series of fluorescein isothiocyanate-labeled peptides up to 1291 Da crossed the PVM in a size-restricted fashion. A labeled peptide of 1926 Da and labeled dextrans and proteins (> or = 3000 Da) failed to transit the PVM. This putative channel in the PVM therefore allows exchange of molecules up to 1300-1900 Da between the host cell cytoplasm and the parasitophorous vacuolar space.

Dopaminergic neuron B20 generates rhythmic neuronal activity in the feeding motor circuitry of Aplysia

We have identified a buccal neuron (B20) that exhibits dopamine-like histofluorescence and that can drive a rhythmic motor program of the feeding motor circuitry of Aplysia. The cell fires vigorously during episodes of patterned buccal activity that occur spontaneously, or during buccal programs elicited by stimulation of identified cerebral command-like neurons for feeding motor programs. Preventing B20 from firing, or firing B20 at inappropriate times, can modify the program driven by the cerebral feeding command-like neuron CBI-2. When B20 is activated by means of constant depolarizing current it discharges in phasic bursts, and evokes a sustained coordinated rhythmic buccal motor program. The program incorporates numerous buccal and cerebral neurons associated with aspects of feeding responses. The B20-driven program can be reversibly blocked by the dopamine-antagonist ergonovine, suggesting that dopamine may be causally involved in the generation of the program. Although firing of B20 evokes phasic activity in cerebral command-like neurons, the presence of the cerebral ganglion is not necessary for B20 to drive the program. The data are consistent with the notion that dopaminergic neuron B20 is an element within the central pattern generator for motor programs associated with feeding.

Alterations in membrane permeability induced by aminoglycoside antibiotics: studies on liposomes and cultured cells

Aminoglycoside antibiotics bind to negatively-charged membranes in vitro as well as in vivo. We have examined if this binding could be associated with a change in the properties of membrane permeability. We have used a series of aminoglycoside derivatives and two independent test systems, namely (i) the release of calcein and of Mn2+ from phosphatidylinositol-containing large unilamellar vesicles, and (ii) the influx of Ca2+ into cultured macrophages. We found that certain aminoglycosides (e.g., streptomycin, isepamicin) markedly increase the membrane permeability whereas others (e.g., gentamicin) barely or do not influence it. This increase, when it occurs, is slower or less extensive than observed with pore-forming agents (mellitin, nystatin) or a Ca(2+)-ionophore (ionomycin). It is not observed with an agent [bis(beta-diethylaminoethylether)hexestrol] known to cause membrane fusion, and is not associated with any detectable change in membrane fluidity. In computer-aided conformational analysis of mixed monolayers between phosphatidylinositol and the aminoglycosides studied, it was found that those derivatives inducing an increase in membrane permeability in our experiments adopted an orientation rather perpendicular to the interface, whereas those with no or only a moderate effect were placed in a parallel orientation to this interface. The perpendicular orientation might cause a local condition of disorder which could explain the effects observed.

Altered expression of unidirectional extrusion routes for methotrexate and cholate in an efflux variant of L1210 cells

The specificity and function of two unidirectional anion-efflux pumps in mouse L1210 cells were evaluated using a variant cell line selected for growth in the presence of cholate and bromosulfophthalein. Transport analysis revealed that cholate efflux in the variant L1210/C7 cell line had declined 8-fold, due to the loss of a bromosulfophthalein-sensitive efflux system, the major extrusion route for cholate in parental cells. Efflux measurements showed further that a bromosulfophthalein-sensitive efflux system for methotrexate was also absent in L1210/C7 cells. Total unidirectional efflux of methotrexate, however, was similar in the variant and parental cells, since the loss in the bromosulfophthalein-sensitive system was compensated by a rise in a second probenecid-sensitive route. The latter was identified from inhibitor studies to be the same system which acts as a minor efflux route for methotrexate in parental cells. These results support the hypothesis that L1210 cells contain a bromosulfophthalein-sensitive efflux system which mediates the unidirectional extrusion of either methotrexate or cholate, and a second probenecid-sensitive route which differs from the bromosulfophthalein-sensitive system in inhibitor specificity and also in its ability to transport methotrexate but not cholate.

Intracellular disposition and metabolism of fluorescently-labeled unmodified and modified oligonucleotides microinjected into mammalian cells

The intracellular distribution and metabolism of microinjected fluorescently-labeled oligonucleotides (ODNs) have been evaluated using confocal fluorescence microscopy. Fluorescent phosphodiester ODNs, microinjected into the cytoplasm of mammalian cells, rapidly accumulate within the nucleus; the fluorescence disappears with a half-life of 15-20 minutes. Microinjected fluorescent phosphorothioate ODNs remain in the nucleus for more than 24 hours. The persistence of fluorescence depends on the length of the ODN. Modification of the 3' end of phosphodiester ODNs does not significantly slow the rapid disappearance of fluorescence, although certain 3' modifications localize ODNs into the cytoplasm. Using specially designed ODNs, endonuclease activity is demonstrated to exist in the cytoplasm and nucleus. Modification of the 2' position of the ribose rings of a fluorescent phosphodiester oligodeoxynucleotide with O-methyl or O-allyl does not alter its intracellular distribution; however, the 2'-O-allyl modification stabilizes the persistence of fluorescence more than 60-fold compared to the 2'-deoxy control. Thus, the experiments indicate that somatic cells contain nucleolytic activities which degrade microinjected ODNs; however, chemical modification can dramatically circumvent this process.

Flow cytometric studies of bicarbonate-mediated Ca2+ influx in boar sperm populations

Boar spermatozoa loaded with the Ca2+ probe fluo-3 were incubated in various Tyrode's-based media similar to those used for in vitro fertilization (IVF), and samples were then analysed by two-colour flow cytometry; propidium iodide was included in the media to detect membrane-damaged ("dead") cells. If media contained bicarbonate/CO2 (a component thought to promote capacitation), part of the live sperm population experienced a considerable influx of Ca2+ into both head and tail compartments. The percentage of responding cells reached a maximum after about 30 min, but both during and after this period there was also a steady increase in the number of dead cells. This bicarbonate-mediated increase in cell death took place in the absence of external Ca2+. Evidence was obtained that the entry of propidium iodide was preceded by a change in permeability of the plasma membrane, detectable by leakage of carboxydichlorofluorescein, and it was therefore deduced that the Ca2+ influx detected by fluo-3 was due to destabilization of the plasma membrane. A similar response could be produced by both caffeine and papaverine (best known as phosphodiesterase inhibitors), but neither cyclic AMP nor activators of adenylate cyclase had any effect. There was no influence of substrate on the process, but, in comparison to poly(vinyl alcohol), serum albumin enhanced it. The precise relevance of this destabilization to capacitation is not yet clear, but it seems significant that the process is mediated or enhanced by components often specifically included in IVF media, and that different individual cells respond after different times.

Platelet activating factor-induced increase in cytosolic calcium and transmembrane current in human macrophages

Platelet-activating factor (PAF) is synthesized and secreted by macrophages in responding to inflammatory stimuli. When exogenously applied to human monocyte derived macrophages (HMDMs), PAF induces a rapid rise in cytosolic free calcium (Cai) believed to be an early triggering event in macrophage activation. We investigated PAF-induced Ca2+ signaling in HMDMs using the calcium indicator Fura-2, combining single cell ratio fluorimetry and digital video imaging with whole-cell recording techniques. Application of PAF (20 ng/ml) to adherent macrophages induced transient increases in Cai that were biphasic, consisting of an initial phase that could be observed in Ca(2+)-free solutions and a second phase that was critically dependent upon Ca2+ entry. When Mn2+ was applied to cells in the presence and absence of Ca2+, PAF increased the rate of Mn2+ entry rate only when Ca2+ was absent. PAF increased the rate of Ba2+ entry even when measured in the presence of external Ca2+. Ca2+ entry was reversibly inhibited in the presence of external La3+ (1 mM). Data obtained from simultaneous voltage-clamp/microfluorimetry experiments demonstrated the activation of a nonselective cation current which closely paralleled the rising phase of the Cai transient. We investigated whether the non-selective cation conductance provided for the bulk of the agonist-induced Ca2+ influx. Changes in Cai following removal of extracellular Ca2+ (Cao) during the agonist-induced Cai response were not associated with changes in whole-cell current. The inability to detect whole-cell current changes correlated with a decrease in Cao suggests that the bulk of the Ca2+ influx was not through the nonselective conductance and either does not occur through a conductance pathway or occurs via a parallel pathway consisting of channels which are both low conductance and highly Ca2+ selective.

Vasopressin elevation of Na+/H+ exchange is inhibited by genistein in human blood platelets

The regulation of intracellular Na+ and pHi in human blood platelets is known to be controlled by the function of the Na+/H+ exchanger. The phosphorylation state of the Na+/H+ exchanger which determines the exchanger activity in human blood platelets is regulated by the activities of protein kinases and protein phosphatases. Observations in this study indicate that arginine vasopressin (AVP) that interacts with a V1 receptor, activates the Na+/H+ exchange in human blood platelets through a genistein-inhibited mechanism. The AVP-activated Na+/H+ exchange is probably not regulated by protein kinase C (PKC), since this activation is not inhibited by staurosporine. The multiple ways in which platelet Na+/H+ exchange can be modulated may indicate the critical role played by this exchanger in the homeostasis control of pHi in human blood platelets.

Flow cytometric analysis of transport activity in lymphocytes electroporated with a fluorescent organic anion dye

Organic anion transport in polarized epithelia and macrophages has previously been studied by monitoring the efflux of fluorescent organic anion dyes from cells. We adapted this strategy to the study organic anion transport in lymphocytes. Cloned lymphoma cells and normal and activated human T cells were loaded with a membrane-impermeant, organic anion dye (Lucifer Yellow) by electroporation. Dye efflux in lymphocytes was rapid, energy-dependent, and inhibitable by organic anion transporter inhibitors. Dye efflux could not be attributed to the effects of electroporation. In addition, electroporated, dye-loaded T helper cells retained the ability to properly respond to specific antigen. Thus, dye loss occurred in viable, functionally competent cells. These experiments demonstrate that electroporation is an effective means of loading cells with Lucifer Yellow, and that lymphocytes possess organic anion transporters that are functionally similar to those previously described for secretory epithelia and macrophages.

Gemfibrozil enhances the listeriacidal effects of fluoroquinolone antibiotics in J774 macrophages

J774 macrophage-like cells express organic anion transporters that promote the efflux of fluoroquinolone antibiotics such as norfloxacin (NFX) from these cells. Gemfibrozil (GFZ) blocks organic anion transport in J774 cells, thereby facilitating the intracellular accumulation of NFX (Cao, C., H.C. Neu, and S.C. Silverstein. 1991. J. Cell Biol. 115:467a [Abstr.]). To determine whether GFZ enhances the efficacy of fluoroquinolone antibiotics against intracellular bacterial pathogens, J774 cells were infected with Listeria monocytogenes and incubated in medium containing a fluoroquinolone antibiotic in the presence or absence of GFZ. Intracellular growth of L. monocytogenes was evaluated by lysing J774 cells and assaying for colony-forming units of Listeria. GFZ intensified the bacteriostatic effect of 4 micrograms/ml NFX and rendered 8 micrograms/ml bactericidal for L. monocytogenes. GFZ had a similar potentiating effect when used in combination with 2 micrograms/ml ciprofloxacin (CFX). CFX plus GFZ was bactericidal for intracellular L. monocytogenes. Treatment of J774 cells with NFX plus GFZ markedly reduced the cytotoxic effect of the bacteria on these cells. Over 55% of cells treated with 8 micrograms/ml NFX alone were dead 16 h after infection, whereas only 5% of cells treated with 8 micrograms/ml NFX plus GFZ were dead at 16 h. Similarly, GFZ potentiated the ability of 2 micrograms/ml to protect J774 cells against the cytocidal effect of Listeria. NFX in combination with GFZ limited cell-to-cell spread of L. monocytogenes. In antibiotic-free medium, > 99% of J774 cells contained intracellular L. monocytogenes at 14 h after infection. NFX alone in the medium did not change this outcome. However, 4 micrograms/ml NFX plus GFZ decreased bacterial spread by approximately 40% at 24 h postinfection, and 8 micrograms/ml NFX plus GFZ prevented all spread beyond the initially infected cell population. These results suggest that GFZ could be used clinically to enhance the efficacy of fluoroquinolone and of other anionic antibiotics against bacteria that grow and/or reside within macrophages and/or other cells.

Inhibition of organic anion transport in endothelial cells by hydrogen peroxide

ATP loss is a prominent feature of cellular injury induced by oxidants or ischemia. How reduction of cellular ATP levels contributes to lethal injury is still poorly understood. In this study we examined the ability of H2O2 to inhibit in a dose-dependent manner the extrusion of fluorescent organic anions from bovine pulmonary artery endothelial cells. Extrusion of fluorescent organic anions was inhibited by probenecid, suggesting an organic anion transporter was involved. In experiments in which ATP levels in endothelial cells were varied by treatment with different degrees of metabolic inhibition, it was determined that organic anion transport was ATP-dependent. H2O2-induced inhibition of organic anion transport correlated well with the oxidant's effect on cellular ATP levels. Thus H2O2-mediated inhibition of organic anion transport appears to be via depletion of ATP, a required substrate for the transport reaction. Inhibition of organic anion transport directly by probenecid or indirectly by metabolic inhibition with reduction of cellular ATP levels was correlated with similar reductions of short term viability. This supports the hypothesis that inhibition of organic anion transport after oxidant exposure or during ischemia results from depletion of ATP and may significantly contribute to cytotoxicity.

A novel cytotoxicity screening assay using a multiwell fluorescence scanner

A new assay using a multiwell fluorescence scanner was developed for screening cytotoxicity to cells cultured in 96-well microtiter plates. The assay is based on binding of propidium iodide to nuclei of cells whose plasma membranes have become permeable due to cell death. Fluorescence of propidium iodide measured with a multiwell fluorescence scanner increased in proportion to the number of permeabilized cells. After ATP depletion of hepatocytes and neonatal cardiac myocytes with metabolic inhibitors ("chemical hypoxia"), and exposure of Madine Darby canine kidney cells to the toxic chemical, HgCl2, propidium iodide fluorescence progressively increased. Increases of fluorescence were linearly proportional with release of lactate dehydrogenase into the culture medium. Employing this cytotoxicity screening assay, protection by various agents against lethal injury was evaluated in cultured hepatocytes during chemical hypoxia. Inhibitors of cysteine proteases (i.e., antipain, leupeptin, E-64), serine proteases (i.e., PMSF), and aspartic acid proteases (i.e., pepstatin A) did not protect against chemical hypoxia. In contrast, 1,10-phenanthroline, an inhibitor of metalloprotease, markedly protected against the onset of cell death during chemical hypoxia. Half-maximal protection after 60 min occurred at 0.5 microM. Phospholipase inhibitors, chlorpromazine (50 microM) and mepacrine (50 microM), also substantially retarded cell killing. U74006F, an inhibitor of lipid peroxidation, slowed cell killing to a lesser extent during chemical hypoxia and after oxidative stress with t-butyl hydroperoxide. Calciphor, a dimer of prostaglandin B1, did not protect against cell killing during chemical hypoxia or t-butyl hydroperoxide toxicity. In conclusion, this high capacity cytotoxicity assay for cells cultured in 96-well microtiter plates is suitable for rapid screening of potential cytoprotective agents in a variety of cell types.

Ligand-affected shift of Na+/H+ exchange pHi set point in human blood platelets, rapidly revealed by a novel approach

The Na+/H+ exchange time-course of BCECF-loaded human platelets, suspended in isotonic media containing NaCl and sodium propionate and activated by intracellular acidification, was measured spectrofluorimetrically. Sequential alkalinization rates decline exponentially as a function of the changing intracellular pH (pHi) and its linear expression (log rate vs. pHi) extrapolates reproducibly to the pHi set point for the Na+/H+ exchange activation. The set point of control platelets (7.28 +/- 0.01) is shifted rapidly (discernibly less than or equal to 30 s) and markedly to alkaline pHi (7.62 +/- 0.03) by PMA, that activates protein kinase C and is shifted to acidic pHi (7.05 +/- 0.01) by staurosporine, which inhibits protein kinases. The addition of 5-N-(3-aminophenyl)amiloride reveals that the alkalinization measured is predominantly Na+/H+ exchange with only a minute contribution (delta pHi = 0.012 +/- 0.002 in 1 min) of an acid loading component, at pHi greater than 7.2. The results support recent studies concluding that the set point indeed reflects the phosphorylation state of the Na+/H+ exchanger.

Intracellular pH modulates cytosolic free magnesium in cultured chicken heart cells

To assess the role of pH in cellular Mg homeostasis, cytosolic pH (pHi) was manipulated by the NH4Cl prepulse technique; pHi, cytosolic Mg2+ (Mgi), and cytosolic Ca2+ (Cai) were measured fluorometrically in single cultured embryonic chicken heart cells loaded with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF), FURAPTRA, and fura-2, respectively. The basal values obtained were as follows: pHi = 7.21 +/- 0.10 (n = 7), [Mg]i = 0.51 +/- 0.08 mM (n = 9), [Ca]i = 126 +/- 15 nM (n = 7). When cells were perfused with 10 mM NH4Cl solution for 5 min, a transient alkalinization (0.53 U) of the cytosol was accompanied by a transient decrease (0.12 mM) in [Mg]i and a transient increase (59 nM) in [Ca]i; these changes approached control levels within 5 min. Upon removal of NH4Cl, a transient acidification (0.89 U) of the cytosol was accompanied by a transient increase (0.10 mM) in [Mg]i and a transient increase (125 nM) in [Ca]i; again, these changes returned toward control levels within 5 min. No significant changes in total cell Mg or Ca were observed during these manipulations. NH4Cl-evoked changes in [Mg]i were not altered significantly by either Mg-free or Ca-free conditions. Changes in [Mg]i were inversely correlated with changes in pHi and were not secondary to changes in [Ca]i. The results suggest that pHi modulates Mgi, probably by affecting cytosolic Mg binding and/or the transport of Mg across subcellular organelles.

Effect of probenecid on phagocytosis and intracellular killing of Staphylococcus aureus and Escherichia coli by human monocytes and granulocytes

The present study concerns the effects of probenecid on the phagocytosis and intracellular killing of Staphylococcus aureus and Escherichia coli by human monocytes and granulocytes. In both monocytes and granulocytes the inhibitory effect on phagocytosis was very small. Inhibition of intracellular killing of S. aureus by monocytes and granulocytes by probenecid was concentration dependent, being half-maximal at about 2 mM probenecid, and near-maximal at about 5 mM probenecid. The intracellular killing could also be inhibited when probenecid was added when this process was already started. Probenecid also inhibited the intracellular killing of E. coli by granulocytes, but not by monocytes. In the concentration range used, probenecid had no toxic effect on phagocytes or bacteria during the 2 hr of the experiments.

Modulation of Na+/H+ exchange and intracellular pH by protein kinase C and protein phosphatase in blood platelets

Phosphorylation of the Na+/H+ exchanger in human platelets is apparently controlled by the balancing activities of protein kinase C (PKC) and protein phosphatase (PP). To explore cellular expressions of these activities, we have examined the impact of modulation of PKC and PP on Na+/H+ exchange activity, its pHi set point and intracellular pH (pHi). These parameters were followed spectrofluorimetrically in BCECF-loaded platelets. Phorbol 12-myristate 13-acetate (PMA) and dihexanoylglycerol (DHG), which stimulate PKC, and okadaic acid, which inhibits PP 1 and 2A, elevate the measured parameters in concert, while staurosporine, which inhibits protein kinases, had opposite effects. The stimulatory and inhibitory effects are similarly very rapid, being discerned within seconds. It is concluded that: (a) phosphorylation of the Na+/H+ exchanger is the common origin of the diverse effects of PMA, DHG, okadaic acid and staurosporine, (b) Na+/H+ exchange properties are tightly regulated by phosphorylation and dephosphorylation, and (c) the exchanger plays a major role in pHi regulation in platelets.

Activation of the inositol trisphosphate second messenger system by cAMP in a mouse fibroblast cell line

Intracellular Ca2+ mobilization events were assessed in mouse L cells, which contain native prostaglandin E1 receptors and transfected human beta 2 adrenergic receptors. Both Fura2 (single cell measurements) and Quin 2, (cuvette assays) were used to determine [Ca2+]i levels. Our results demonstrate that in the transfected cells there is a dose-dependent increase in [Ca2+]i in response to isoproterenol (0.1 nM-100 nM), which is inhibited by the beta-adrenergic antagonist, propranolol, and is a result of intracellular Ca2+ release. [Ca2+]i in these cells was also increased by prostaglandin E1, 8 bromo cyclic AMP, and aluminum fluoride. Both 8 bromo cAMP and isoproterenol induced a rapid increase in the levels of IP1, IP2, and IP3. The data presented demonstrate that the elevation of intracellular cyclic AMP induces an increase in IP3 production which leads to an elevation in [Ca2+]i. We propose that this cyclic AMP dependent activation of the IP3 generating system occurs at a post-receptor site.