Axoplasmic transport of mitochondria in cultured dorsal root ganglion cells

Targeting NMNAT1 to axons and synapses transforms its neuroprotective potency in vivo

Axon and synapse degeneration are common components of many neurodegenerative diseases, and their rescue is essential for effective neuroprotection. The chimeric Wallerian degeneration slow protein (Wld(S)) protects axons dose dependently, but its mechanism is still elusive. We recently showed that Wld(S) acts at a non-nuclear location and is present in axons. This and other recent reports support a model in which Wld(S) protects by extranuclear redistribution of its nuclear NMNAT1 portion. However, it remains unclear whether cytoplasmic NMNAT1 acts locally in axons and synapses or at a non-nuclear site within cell bodies. The potency of axon protection by non-nuclear NMNAT1 relative to Wld(S) also needs to be established in vivo. Because the N-terminal portion of Wld(S) (N70) localized to axons, we hypothesized that it mediates the trafficking of the NMNAT1 portion. To test this, we substituted N70 with an axonal targeting peptide derived from amyloid precursor protein, and fused this to NMNAT1 with disrupted nuclear targeting. In transgenic mice, this transformed NMNAT1 from a molecule unable to inhibit Wallerian degeneration, even at high expression levels, into a protein more potent than Wld(S), able to preserve injured axons for several weeks at undetectable expression levels. Preventing NMNAT1 axonal delivery abolished its protective effect. Axonally targeted NMNAT1 localized to vesicular structures, colocalizing with extranuclear Wld(S), and was cotransported at least partially with mitochondria. We conclude that axonal targeting of NMNAT activity is both necessary and sufficient to delay Wallerian degeneration, and that promoting axonal and synaptic delivery greatly enhances the effectiveness.

Tumor necrosis factor-alpha induces changes in mitochondrial cellular distribution in motor neurons

Motor neuron (MN) mitochondrial abnormalities and elevation in spinal fluid levels of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). The mechanism of neuron death in ALS remains unclear, along with the contributions of mitochondrial dysfunction and inflammation in the process. Cell cultures enriched for MN derived from embryonic rat spinal cords were established and directly exposed in vitro to recombinant TNF-alpha for varying lengths of time. Although cytokine exposure for up to 4 days failed to induce MN death, mitochondrial changes were observed shortly after initiating treatment. Our results demonstrate that TNF-alpha induced mitochondrial redistribution toward the soma in MN. We postulate that inflammation may precede, and in fact cause, the mitochondrial changes observed in ALS tissue.

Application of simple photobleaching microscopy techniques for the determination of the balance between anterograde and retrograde axonal transport

The directionality of axonal transport represents an important question in neurophysiological and neuropathological research. Various approaches such as videomicroscopy, radioisotopic and fluorescence-based techniques are used. Recently, a novel FRAP-based (fluorescent recovery after photobleaching) technique using synaptophysin-EGFP expression in primary neurons was applied, allowing reliable and sensitive evaluation of gross axonal transport changes using confocal live-imaging microscopy. Here, we describe a novel FLIP-based (fluorescence loss in photobleaching) approach using a synaptophysin-EGFP probe that allows the differential evaluation of the ante- and retrograde transport parameters. Furthermore, we improved the sensitivity of the probe by substituting EGFP with an ECFP/VenusYFP fusion FRET (fluorescence resonance energy transfer) pair. The use of this FRET couple improves the precision of axonal transport measurements by combining FLIP and FLAP (fluorescence localization after photobleaching) techniques and eliminating the need for pre-bleaching images and thus pixel shifts between various exposures, and by reducing the deleterious effect of photobleaching.

Neuropeptide Y inhibits axonal transport of particles in neurites of cultured adult mouse dorsal root ganglion cells

Neuropeptide Y (NPY) plays a modulatory role in processing nociceptive information. The present study investigated the effects of NPY on axonal transport of particles in neurites of cultured adult dorsal root ganglion (DRG) cells using video-enhanced microscopy. Application of NPY decreased the number of particles transported in both the anterograde and retrograde directions. This effect was persistently observed during NPY application and was reversed after washout. The inhibitory effect of NPY was concentration dependent between 10(-9) M and 10(-6) M. The instantaneous velocity of individual particles moving in anterograde and retrograde directions was also reduced by NPY. Both the NPY Y1 receptor agonist [Leu31,Pro34]-NPY and NPY Y2 receptor agonist NPY(13-36) mimicked the effect of NPY on the number of transported particles. An immunocytochemical study using an antiserum against the NPY Y1 receptor protein revealed that the Y1 receptor was expressed in the majority (85.9 %) of cultured adult mouse DRG cells. Pre-treatment of cells with pertussis toxin, a GTP-binding protein (G protein) inhibitor, completely blocked the inhibitory effect of NPY. Each application of SQ-22536, an adenylate cyclase inhibitor, and H-89, a protein kinase A inhibitor, mimicked and occluded the effect of NPY. In contrast, dibutyryl cAMP (dbcAMP), a membrane permeable cAMP analogue, and forskolin, an activator of adenylate cyclase, produced a transient increase in axonal transport. The application of dbcAMP and forskolin in combination with NPY negated the effect of NPY alone. These results suggest that NPY, acting at Y1 and Y2 receptors, inhibits axonal transport of particles in sensory neurones. The effect seems to be mediated by a pertussis toxin-sensitive G protein, adenylate cyclase, and protein kinase A pathway. Therefore, NPY may be a modulatory factor for axonal transport in sensory neurones.

Effects of ALCAR on the fast axoplasmic transport in cultured sensory neurons of streptozotocin-induced diabetic rats

The effects of acetyl-L-carnitine (ALCAR) on fast axoplasmic transport were studied in cultured dorsal root ganglion (DRG) neurons of diabetic rats. Three-month-old male rats were used 7 days after streptozotocin injection. Neurons obtained from ganglia were cultured with a high concentration of glucose. The amount and the mean velocity of retrogradely transported particles, reduced in the diabetic animal, were transiently recovered by 1 mM ALCAR. The number of particles moving at 0.8-1.2 microm/s, considered to be lysosomes, increased in the velocity distribution. ALCAR did not modify the amount and mean velocity of anterograde particles which were unaffected by diabetes, or of bidirectional particles in neurons of control rats. This study suggests that diabetic neuropathy may be relieved by ALCAR via recovering retrograde axoplasmic transport.

Axoplasmic transport and its signal transduction mechanism

Neuron requires a continual supply of materials synthesized in the cell body, for example a wide range of soluble proteins, membranous components, and various organelles. The transported materials are needed to replace constituents that turn over in the membrane and organelles of the fiber and also are needed to bring substances participating in energy metabolism. Other transported components are neurotransmitters or transmitter-related components supplied to the nerve terminals for the release and subsequent excitation of postsynaptic cells. Moreover, neurotropic substances and modulators are released from the nerve terminals to affect the functional state of the neuron. Conversely, some materials are conveyed back to the cell body. These include organelles, lysosomes, nerve growth factor, and selected small molecules such as adenosine, Ca2+, and some neurotransmitters. Axoplasmic transport is thought to be fundamental for a variety of neuronal cell functions. Thus it may be considered that axoplasmic transport relates to the dynamic physiological activity of neurons; in other words, axoplasmic transport is supposed to express the physiological activity of neurons. In turn, as in the case for many other physiological functions, axoplasmic transport is possibly controlled by neuronal, hormonal, and immunological systems. Since axoplasmic transport supplies neuron materials toward the synapses and back to the cell body, a feedback system of regulatory mechanisms of a variety of neuronal functions might be operated through axoplasmic transport pathways. Although axoplasmic transport is the important neuronal function, its regulation is poorly understood. In this review, we focus on the dynamics of organelle transport and its regulatory mechanisms mediated by neurotransmitters.

Axonal structure and function after axolemmal leakage in the squid giant axon

Membrane leakage is a common consequence of traumatic nerve injury. In order to measure the early secondary effects of different levels of membrane leakage on axonal structure and function we studied the squid giant axon after electroporation at field strengths of 0.5, 1.0, 1.6, or 3.3 kV/cm. Immediately after mild electroporation at 0.5 kV/cm, 40% of the axons had no action potentials, but by 1 h all of the mildly electroporated axons had recovered their action potentials. Many large organelles (mitochondria) were swollen, however, and their transport was reduced by 62% 1 h after this mild electroporation. One hour after moderate electroporation at 1.0 kV/cm, most of the axons had no action potentials, most large organelles were swollen, and their transport was reduced by 98%, whereas small organelle transport was reduced by 75%. Finally at severe electroporation levels of 1.65-3.0 kV/cm all conduction and transport was lost and the gel-like axoplasmic structure was clumped or liquefied. The structural damage and transport block seen after severe and moderate poration were early secondary injuries that could be prevented by placing the porated axons in an intracellular-type medium (low in Ca2+, Na+, and Cl-) immediately after poration. In moderately, but not severely, porated axons this protection of organelle transport and structure persisted, and action potential conduction returned when the axons were returned to the previously injurious extracellular-type medium. This suggests that the primary damage, the axolemmal leak, was repaired while the moderately porated axons were in the protective intracellular-type medium.

A novel action of collapsin: collapsin-1 increases antero- and retrograde axoplasmic transport independently of growth cone collapse

Chick collapsin-1, a member of the semaphorin family, has been implicated in axonal pathfinding as a repulsive guidance cue. Collapsin-1 induces growth cone collapse via a pathway which may include CRMP-62 and heterotrimeric G proteins. CRMP-62 protein is related to UNC-33, a nematode neuronal protein required for appropriately directed axonal extension. Mutations in unc-33 affect neural microtubules, the basic cytoskeletal elements for axoplasmic transport. Using computer-assisted video-enhanced differential interference contrast microscopy, we now demonstrate that collapsin-1 potently promotes axoplasmic transport. Collapsin-1 doubles the number of antero- and retrograde-transported organelles but not their velocity. Collapsin-1 decreases the number of stationary organelles, suggesting that the fraction of time during which a particle is moving is increased. Collapsin-1-stimulated transport occurs by a mechanism distinct from that causing growth cone collapse. Pertussis toxin (PTX) but not its B oligomer blocks collapsin-induced growth cone collapse. The holotoxin does not affect collapsin-stimulated axoplasmic transport. Mastoparan and a myelin protein NI-35 induce PTX-sensitive growth cone collapse but do not stimulate axoplasmic transport. These results provide evidence that collapsin has a unique property to activate axonal vesicular transport systems. There are at least two distinct pathways through which collapsin exerts its actions in developing neurons.

Effect of dibutyryl cyclic AMP on axoplasmic transport in the hippocampus

The effect of dibutyryl cyclic AMP (dbcAMP) on axoplasmic transport of cultured hippocampal neuron cells from postnatal 1-day mice was analyzed with a computer-assisted video-enhanced differential interference contrast microscope system. Dibutyryl cyclic AMP increased the axoplasmic transport in both anterograde and retrograde directions. The number of particles flowing in the neurites was increased by 0.5 mM dbcAMP. The peak reached about 160% of the initial value. The instantaneous velocity of axoplasmic transport was also increased by 0.5 mM dbcAMP. The average velocity of anterograde and retrograde direction changed respectively from 1.95 +/- 1.01 microm/s (n = 55) to 2.66 +/- 1.26 microm/s (n = 58) and from 1.94 +/- 0.85 (n = 57) to 2.39 +/- 0.93 (n = 57). Rates were 136.1 and 123.1%, respectively. Previously, we have found that acetylcholine suppressed and adrenaline increased the axoplasmic transport in superior cervical ganglion cells. These effects are related to the amount of endogeneous cAMP. The results of the present report suggest that endogeneous cAMP is also related to hippocampal axoplasmic transport.

Localization of D1 dopamine receptors on live cultured striatal neurons by quantitative fluorescence microscopy

Single neurons in culture express a heterogeneity of neurotransmitter receptor subtypes. The study of the effects of neurotransmitters on neuronal function is complicated by this heterogeneity. It would therefore be useful to be able to identify live neurons that express the receptors of interest and then use these neurons for functional studies. We have used quantitative fluorescence microscopy to identify single live striatal neurons that express D1 dopamine receptors. The binding of the fluorescent D1 dopamine receptor antagonist bodipy-SCH 23390 was measured in 2-3-week-old primary striatal cultures derived from fetal rats (embryonic day 18). Binding of bodipy-SCH 23390 to live neurons was displaced by (+)-butaclamol, dopamine or SCH 23390, indicating that it specifically labelled D1 dopamine receptors. However, the fraction of bodipy-SCH 23390 binding that was specific varied substantially among individual neurons indicating heterogeneity of D1 dopamine receptor expression. Interestingly, bodipy-SCH 23390 also specifically labelled discrete spots of receptors on the neuronal processes. This technique should prove useful in the study of the effects of dopaminergic drugs on neuronal function in primary culture.

Signal transduction mechanism responsible for changes in axoplasmic transport caused by neurotransmitters

Transduction mechanism for modulation of axoplasmic transport by neurotransmitters was studied using cultured mouse superior cervical ganglion cells. The transported particles were analyzed with a computer-assisted video-enhanced differential interference contrast microscope system. Acetylcholine depressed and adrenaline increased axoplasmic transport. GTP-binding proteins linked with both receptors activate or inactivate adenylyl cyclase, thereby altering the intracellular concentration of cyclic AMP. The cyclic AMP activates protein kinase A, which phosphorylates certain enzymes and the enzymes in turn phosphorylate motor proteins. An inhibitor protein kinase A, KT5720, decreases the number of the transported particles. In a stable state the cyclic AMP level stays at a normal level. Treatment with neurotransmitters causes a change in this level, which changes the activity of protein kinase A and thus decreases or enhances the phosphorylation of motor proteins. These changes are involved in the modulation of axoplasmic transport.

Effects of acetylcholine and adrenaline on axoplasmic transport at different regions of mouse superior cervical ganglion cells in culture

Adrenaline and acetylcholine (ACh) were applied locally at three different positions in cultured superior cervical ganglion cells, i.e., cell body, neurite, and growth cone and the effects on the axoplasmic transport were measured with a video-enhanced microscope. Local ACh application to the cell body, neurite, and growth cone caused the same decreasing effect, but the effects of local adrenaline application were different from each other. Local adrenaline application to the cell body and growth cone caused an increase of axoplasmic transport, but local application at the neurite caused no effect. These data may indicate that there was a lack of beta 2 adrenergic receptors in the neurite. Desensitization of axoplasmic transport was also examined in the SCG neurons. Repetitive adrenaline application to the cell body caused desensitization to the stimulus of adrenaline application.

Differential suppression of axoplasmic transport: effects of light irradiation to the growth cone of cultured dorsal root ganglion neurons

1. Growth cones of cultured dorsal root ganglion neurons from mice were irradiated using a mercury lamp. 2. The flux of particles of fast retrograde axoplasmic transport decreased promptly after light irradiation without a change in velocity. 3. That of anterograde transport decreased as well, but with a significant latency. The decrease in anterograde flux was attributed to decreased velocity of particles. 4. Video-enhanced contrast microscopy of growth cones revealed transient swelling of growth cones and transient stagnation of particles in growth cones. 5. The longer the neurite, the larger the latency of the change of the anterograde transport; peripheral information was calculated to be conveyed to the cell body at a speed of 6 microns/min. 6. The mechanism of this information conveyance and the export of materials from the cell body are discussed.

Aspergillus nidulans apsA (anucleate primary sterigmata) encodes a coiled-coil protein required for nuclear positioning and completion of asexual development

Many fungi are capable of growing by polarized cellular extension to form hyphae or by isotropic expansion to form buds. Aspergillus nidulans anucleate primary sterigmata (apsA) mutants are defective in nuclear distribution in both hyphae and in specialized, multicellular reproductive structures, called conidiophores. apsA mutations have a negligible effect on hyphal growth, unlike another class of nuclear distribution (nud) mutants. By contrast, they almost completely block entry of nuclei into primary buds, or sterigmata (bud nucleation), produced during development of conidiophores. Failure of the primary sterigmata to become nucleated results in developmental arrest and a failure to activate the transcriptional program associated with downstream developmental steps. However, occasionally in mutants a nucleus enters a primary bud and this event relieves the developmental blockage. Thus, there is a stringent developmental requirement for apsA function, but only at the stage of primary bud formation. apsA encodes a 183-kD coiled-coil protein with similarity to Saccharomyces cerevisiae NUM1p, required for nuclear migration in the budding process.

Effect of neurotransmitters on axoplasmic transport: how adrenaline affects superior cervical ganglion cells

The effect of adrenaline on the axoplasmic transport of cultured superior cervical ganglion cells was analyzed with a computer-assisted video-enhanced differential interference contrast microscope system. Adrenaline increased the axoplasmic transport reversibly in both anterograde and retrograde directions. A beta 2-antagonist, butoxamine, antagonized the increasing effects of adrenaline, but alpha-antagonists and beta 1-antagonists did not. A beta 2-agonist, albuterol, mimicked the adrenaline effect, but beta 1-, alpha 1-, alpha 2-agonists did not. The adrenaline receptor may be a beta 2-receptor. Dibutyryl cyclic AMP and forskolin increased the axoplasmic transport. Therefore, adrenaline increases the axoplasmic transport by raising the cyclic AMP level. In light of our former report that acetylcholine suppresses the axoplasmic transport, neurotransmitters control axoplasmic transport and this neurotransmitter control reflects the activity of the nerve cell.

Coexistence of substance P, neuropeptide Y, VIP, and CGRP in the nerve fibers of the carotid labyrinth of the bullfrog, Rana catesbeiana: a double-labelling immunofluorescence study in combination with alternate consecutive sections

Double immunohistochemical staining with rhodamine- and fluorescein isothiocyanate (FITC)-conjugated antisera revealed the coexistence of substance P (SP) and neuropeptide Y (NPY), and SP and calcitonin gene-related peptide (CGRP) in most nerve fibers in the intervascular stroma of the carotid labyrinth of the bullfrog, Rana catesbeiana, although there were a few fibers which showed only SP- or NPY-immunoreactivity. Approximately one third of SP-immunoreactive fibers also showed coexistence with vasoactive intestinal polypeptide (VIP)-immunoreactivity, and a few fibers contained VIP without SP. The combination of the double immunofluorescence technique and alternate consecutive sections further demonstrated the possible coexistence of SP, VIP, NPY, and CGRP. This coexistence of four different peptides in the same nerve fibers was proved by the following two evident facts: 1) some SP fibers which demonstrated coexistence with NPY-immunoreactivity were assumed to be continuous with those showing VIP-immunoreactivity, and 2) almost all of the SP fibers showed coexistence with CGRP-immunoreactivity. By this reasoning, nearly one third of SP fibers may demonstrate coexistence with NPY-, VIP-, and CGRP-immunoreactivities. These multiple peptides might be involved in vascular regulatory function, which is a possible function of the amphibian carotid labyrinth.

Bradykinin-responsive cells of dorsal root ganglia in culture: cell size, firing, cytosolic calcium, and substance P

1. We analyze bradykinin-sensitive cells of the mouse dorsal root ganglion in culture from the viewpoints of cell size, electrical responses, and Ca2+ concentration change due to bradykinin and immunocytochemistry of substance P. 2. Sixteen percent of cells in the cell group 26-30 microns in diameter fired in response to 10 microM bradykinin. None of other cell groups showed a firing response to bradykinin. 3. We measured a cytosolic Ca2+ change due to bradykinin using a Ca(2+)-sensitive fluorescent dye, Fura 2. The rapid rise (peak time, 20 sec) in the Ca2+ concentration was ascribed to Ca2+ release from intracellular Ca2+ stores. The profound change in the Ca2+ concentration was observed again in the cell group 26-30 microns in diameter. Seventeen percent of cells in this group increased the Ca2+ concentration by approximately seven times that at resting level. 4. Among cells which increase Ca2+ concentration responding to bradykinin, 83% of them contain substance P (an immunocytochemical study). 5. We conclude that 16-17% of the cell group 26-30 microns in diameter of the dorsal root ganglia in culture are polymodal nociceptors and respond to bradykinin.

Mechanism of inhibitory action of capsaicin on particulate axoplasmic transport in sensory neurons in culture

The inhibitory effect of capsaicin on axoplasmic transport in cultured dorsal root ganglion cells was analyzed by video-enhanced contrast microscopy. Capsaicin inhibited particle transports in a dose-dependent manner, irrespective of the diameter of axons. The effect of capsaicin was reversible at low concentrations. Capsaicin affected both the anterograde and retrograde transport. Large organelles were more sensitive to capsaicin than small ones in the retrograde transport. An experiment using calcium-sensitive dye, Fura 2, indicated that capsaicin raised the intraneuronal free calcium concentration preceding the inhibition of the transport. Electron microscopy revealed that microtubules and neurofilaments are disorganized and disoriented by capsaicin. We reached a conclusion that capsaicin inhibits fast axoplasmic transport of both anterograde and retrograde directions in all types of somatosensory neurons in culture by disorganizing intraaxonal cytoskeletal structures, through the elevated intracellular Ca2+ concentration.

The regulation of bidirectional mitochondrial transport is coordinated with axonal outgrowth

Although small molecules such as ATP diffuse freely in the cytosol, many types of cells nonetheless position their mitochondria in regions of intense ATP consumption. We reasoned that in the highly elongated axonal processes of growing neurons in culture, the active growth cone would form a focus of ATP consumption so distant from the cell body as to require the positioning of mitochondria nearby via regulated axonal transport. To test this hypothesis, we quantified the distribution and transport behavior of mitochondria in live, aerobically respiring chick sympathetic neurons. We found that in the distal region of actively growing axons, the distribution of mitochondria was highly skewed toward the growth cone, with a sevenfold higher density in the region immediately adjacent to the growth cone than in the region 100 microns away. When axonal outgrowth was blocked by substratum-associated barriers or mild cytochalasin E treatment, the gradient of mitochondrial distribution collapsed as mitochondria exited retrogradely from the distal region, becoming uniformly distributed along the axon within one hour. Analysis of individual mitochondrial behaviors revealed that mitochondrial movement everywhere was bidirectional but balanced so that net transport was anterograde in growing axons and retrograde in blocked axons. This reversal in net transport derived from two separate modulations of mitochondrial movement. First, moving mitochondria underwent a transition to a persistently stationary state in the region of active growth cones that was reversed when growth cone activity was halted. Second, the fraction of time that mitochondria spent moving anterogradely was sharply reduced in non-growing axons. Together, these could account for the formation of gradients of mitochondria in growing axons and their dissipation when outgrowth was blocked. This regulated transport behavior was not dependent upon the ability of mitochondria to produce ATP. Our data indicate that mitochondria possess distinct motor activities for both directions of movement and that mitochondrial transport in axons is regulated by both recruitment between stationary and moving states, and direct regulation of the anterograde motor.

The expression of CD15 in dissociated cultured rat dorsal root ganglion cells

This study describes the presence of CD15 in dorsal root ganglia neurons in five experimental conditions: chemically defined medium and the same medium with added nerve growth factor, retinoic acid or antibodies against insulin or tyrosine phosphate. Positive astrocyte controls were used to differentiate the monoclonal antibodies that did not react with CD15. Those monoclonal antibodies which detected CD15 in this positive control were also used to study CD15 positivity in dorsal root ganglion cells. This study shows: (i) masking of the CD15 antibody, which influences the detection capacity of the monoclonal antibodies used; (ii) that CD15 discerns two subpopulations of DRG neurons: a CD15-positive and a CD15-negative population; (iii) that CD15 expression is not involved in the outgrowth of protrusions or the wrapping by non-neuronal cells of DRG neurons.

Effect of neurotransmitters on axoplasmic transport: acetylcholine effect on superior cervical ganglion cells

The effect of acetylcholine (ACh) on particle movements along axons of cultured superior cervical ganglion cells was analyzed with a computer-assisted video-enhanced differential interference contrast microscope system. ACh suppressed the axoplasmic transport reversibly in both anterograde and retrograde directions. A muscarinic agonist, arecoline, mimicked the ACh effect, but nicotine did not. An experiment with the Ca(2+)-indicator dye, fura-2, revealed that ACh suppressed the transport without any change of intracellular Ca2+ concentration. ACh also suppressed the axoplasmic transport in Ca(2+)-free medium. Islet-activating protein (IAP), pertussis toxin, blocked the ACh effect. These results indicate that ACh activates muscarinic receptors and suppresses fast axoplasmic transport through the activation of IAP-sensitive GTP-binding protein, irrespective of Ca2+ ions.

Theoretical analysis of lipid transport in sciatic nerve

We modify our previous mathematical model of axonal transport to analyze data on the fast transport of lipids in rat sciatic nerve given in Toews et al. (J. Neurochem. 40, 555-562 (1983)). The theoretical model accounts well for the shapes of the profiles of phosphatidylcholine, phosphatidylethanolamine, cholesterol and diphosphatidylglycerol. The parameters obtained support the qualitative conclusions of Toews et al. and provide quantitative estimates of the underlying processes, e.g., rates of vesicle and mitochondria translocation, rate constants for association and dissociation between vesicles, kinesin and microtubules, rates of deposition and rates of loss of each class of lipid from the nerve by leakage or via removal by the retrograde transport system. The analysis suggests that two classes of vesicles moving at different speeds may be involved in the transport of phosphatidylcholine and phosphatidylethanolamine.

Increase in intracellular calcium induced by stimulating histamine H1 receptors in macrophage-like P388D1 cells

The addition of histamine to macrophage-like P388D1 cells resulted in a dose-dependent increase in intracellular calcium [Ca2+]i measured by fura-2 in single cells. The maximum level of [Ca2+]i was obtained by addition of 1 x 10(-4) M histamine. The increase was primarily due to release from the intracellular store. The addition of an H1 specific antagonist pyrilamine before histamine treatment inhibited the increase reversibly, while an H2 specific antagonist cimetidine had no inhibitory effect. Histamine also resulted in a dose-dependent increase in cGMP but not in cAMP. These data suggest the existence of histamine H1 receptors in these cells and histamine may have some biological effect on the function of macrophages via [Ca2+]i and cGMP as the second messengers.