Enhanced antigen cross-presentation in human colorectal cancer-associated fibroblasts through upregulation of the lysosomal protease cathepsin S

Background

Cross-presentation of exogenous antigens in HLA-class I molecules by professional antigen presenting cells (APCs) is crucial for CD8+ T cell function. Recent murine studies show that several non-professional APCs, including cancer-associated fibroblasts (CAFs) also possess this capacity. Whether human CAFs are able to cross-present exogenous antigen, which molecular pathways are involved in this process and how this ultimately affects tumor-specific CD8+ T cell function is unknown.

Methods

In this study, we investigated the ability of human colorectal cancer (CRC)-derived CAFs to cross-present neoantigen-derived synthetic long peptides (SLPs), corresponding to tumor-derived mutant peptides, and how this affects tumor-specific T-cell function. Processing of the SLP was studied by targeting components of the cross-presentation machinery through CRISPR/Cas9 and siRNA-mediated genetic ablation to identify the key molecules involved in fibroblast-mediated cross-presentation. Multispectral flow cytometry and killing assays were performed to study the effect of fibroblast cross-presentation on T cell function.

Results

Here, we show that human CRC-derived CAFs display an enhanced capacity to cross-present neoantigen-derived SLPs when compared with normal colonic fibroblasts. Cross-presentation of antigens by fibroblasts involved the lysosomal protease cathepsin S. Cathepsin S expression by CAFs was detected in situ in human CRC tissue, was upregulated in ex vivo cultured CRC-derived CAFs and showed increased expression in normal fibroblasts after exposure to CRC-conditioned medium. Cognate interaction between CD8+ T cells and cross-presenting CAFs suppressed T cell function, reflected by decreased cytotoxicity, reduced activation (CD137) and increased exhaustion (TIM3, LAG3 and CD39) marker expression.

Conclusion

These data indicate that CAFs may directly suppress tumor-specific T cell function in an antigen-dependent fashion in human CRC.

Extracolonic cancer risk in Dutch patients with APC (adenomatous polyposis coli)-associated polyposis

BACKGROUND

Screening of patients with familial adenomatous polyposis (FAP) have led to a substantial reduction in mortality due to colorectal cancer (CRC). Recent guidelines suggest that surveillance of non-intestinal malignancies should also be considered in those patients. However, the value of these surveillance programmes is unknown. The aims of this study were (1) to assess the occurrence of extracolonic malignancies in a large series of adenomatous polyposis coli (APC) mutation carriers and (2) to evaluate the causes of death.

METHODS

All APC mutation carriers were selected from the Dutch polyposis registry. Data on causes of death were collected. Pathology reports were retrieved from the Dutch Pathology Registry.

RESULTS

A total of 85 extracolonic malignancies were diagnosed in 74 of 582 APC mutation carriers. Duodenal and skin cancers were the most prevalent cancers. Thyroid cancer was observed in only 1.5% of the cases. The main cause of death was cancer (59% of all deaths), with 42% due to CRC and 21% due to duodenal cancer. One patient died from thyroid cancer. The second and third most common causes of death were cardiovascular disease (13% of all deaths) and desmoid tumours (11% of all deaths), respectively.

CONCLUSION

Extending surveillance programmes to other cancers will not contribute significantly to the survival of patients with FAP.

Narrow-band imaging compared with conventional colonoscopy for the detection of dysplasia in patients with longstanding ulcerative colitis

BACKGROUND AND STUDY AIM

Patients with longstanding ulcerative colitis are at increased risk of developing colorectal cancer. Colonoscopic surveillance is advised, but the detection of neoplasia by conventional colonoscopy is difficult. The aim of this study was to compare the accuracy of narrow-band imaging (NBI), a new imaging technique, with standard colonoscopy for the detection of neoplasia in patients with longstanding ulcerative colitis.

PATIENTS AND METHODS

This was a prospective, randomized, crossover study of 42 patients with longstanding ulcerative colitis. All participants underwent NBI and conventional colonoscopy with at least 3 weeks between the procedures. Randomization determined the order of the examinations. Targeted biopsies were taken during both procedures; additional random biopsies were taken at conventional colonoscopy only. The number of patients with neoplasia detected by targeted biopsies was used to assess the sensitivity for each technique.

RESULTS

With NBI, 52 suspicious lesions were detected in 17 patients, compared with 28 suspicious lesions in 13 patients detected during conventional colonoscopy. Histopathological evaluation of targeted biopsies revealed 11 patients with neoplasia: in four patients the neoplasia was detected by both techniques, in four patients neoplasia was detected only by NBI, and in three patients neoplasia was detected only by conventional colonoscopy ( P = 0.705). Aside from targeted biopsies, 1522 random biopsies were taken. These revealed one additional patient with dysplasia that was not detected by either technique.

CONCLUSIONS

The sensitivity of the studied first-generation NBI system for the detection of patients with neoplasia seems to be comparable to conventional colonoscopy, although more suspicious lesions were found during NBI. We believe that it is still too early to stop taking additional random biopsies at surveillance colonoscopy in patients with ulcerative colitis.

Altered bone morphogenetic protein signalling in the Helicobacter pylori-infected stomach

Morphogens regulate epithelial cell fate decisions in the adult gastrointestinal tract. The authors hypothesized that influx of inflammatory cells into the lamina propria may disturb the normal expression gradients of morphogens (morphogenetic landscape) in gastrointestinal epithelia. Changes in the activity of the bone morphogenetic protein (BMP) pathway in normal and Helicobacter pylori-infected gastric mucosa were therefore examined. It is shown that BMP receptors, the activated (phosphorylated) form of the intracellular BMP signal transduction protein SMAD1, and BMP target ID2 all localize to gastric epithelial cells that are at the end of the axis of epithelial renewal in normal mucosa. Colonization of human gastric mucosa with H. pylori was associated with an increase in BMP2 expression due to influx of inflammatory cells that produce BMP2. Furthermore, whereas no BMP4 was detected in the normal antrum, focal infiltrates of BMP4-expressing cells were found in the H. pylori-infected stomach. This influx of BMP-expressing cells was associated with an increase in epithelial BMP signalling. Interestingly, a shift in activity of the BMP pathway was observed towards the precursor cell compartment (isthmus) of the gastric units. Thus, H. pylori infection results in an influx of inflammatory cells that disturb the normal activity gradient of a morphogenetic pathway with an established role in epithelial cell fate regulation. The data suggest that morphological changes in epithelial histology may result from alterations in the morphogenetic landscape secondary to changes in the cellular composition of the lamina propria.

Sonic hedgehog regulates gastric gland morphogenesis in man and mouse

BACKGROUND & AIMS

Gastric epithelial renewal is an asymmetric process. A stem cell located halfway up the tubular unit gives rise to both a basal gland region and a luminal pit compartment, but the mechanisms responsible for the maintenance of this asymmetry are obscure. We investigated whether Sonic hedgehog (Shh), an established polarizing signal protein during development, is expressed and functional in the adult human and murine stomach.

METHODS

Expression of Shh and putative transcriptional targets was investigated using immunoblot and immunohistochemistry. Mice were treated with the Shh inhibitor cyclopamine and examined for expression levels of Shh targets and proliferation of gastric epithelial cells.

RESULTS

Shh was expressed in the stomach. In cyclopamine-treated mice, we observed decreased expression of HNF3beta, Islet (Isl)-1 and BMP4, 3 putative Shh target genes. Inhibition of Shh markedly enhanced gastric epithelial proliferation and affected the cell cycle of gastric epithelial gland cells, whereas pit cells remained unaffected.

CONCLUSIONS

Shh controls the expression of at least 3 factors important for epithelial differentiation and is a negative regulator of gastric gland cell proliferation. Shh is a candidate polarizing signal in the maintenance of gastric pit-gland asymmetry.

Leptin is a growth factor for colonic epithelial cells

BACKGROUND AND AIMS

Obesity increases the risk of colon cancer, whereas physical activity reduces the risk. Plasma levels of leptin increase in proportion to the level of obesity and are reduced by physical activity. Leptin acts as a growth factor for several cell types and thus may provide a biological explanation for the observed epidemiological risk factors. The aim of this study was to investigate whether leptin is a growth factor for colonic epithelial cells.

METHODS

The presence of the leptin receptor in human colon cancer cell lines was assessed using reverse-transcription polymerase chain reaction and immunoblotting, and its presence in human colonic tissue was assessed by immunohistochemistry. The effects of leptin in vitro on HT29 cells were assessed by assessing p42/44 mitogen-activated protein kinase phosphorylation, thymidine incorporation, and cell numbers and in vivo in C57BL/6 mice by colonic bromodeoxyuridine incorporation.

RESULTS

The leptin receptor is expressed in human colon cancer cell lines and human colonic tissue. Stimulation with leptin leads to phosphorylation of p42/44 mitogen-activated protein kinase and increases proliferation in vitro and in vivo.

CONCLUSIONS

Leptin is a growth factor in colonic epithelial cells and one that may provide a biological explanation for the observed associations between obesity, physical activity, and colon cancer.

Can cardiotocography prior to induction of labour predict obstetric intervention? A pilot study

We set out to study the value of cardiotocography (CTG) performed before induction of labour for prolonged pregnancy in predicting obstetric intervention. This was a prospective observational study, based in a district general hospital. We studied 100 consecutive patients who underwent induction of labour for prolonged pregnancy. Cardiotocographs (CTGs) were performed before induction of labour on the tenth day after the estimated date of confinement (290 days). The CTGs were then reviewed without knowledge of the outcome of the induction of labour. Obstetric outcomes were then compared. The main outcome measures were the intrapartum presence or absence of meconium stained liquor and the necessity for obstetric intervention. Ninety per cent of CTGs were normal. There was no difference found between the two groups for operative delivery or the presence of meconium liquor. Caesarean section was more likely in the group with an abnormal CTG before induction of labour, but the possibility of this being due to chance is high in this study. There was one case of undiagnosed growth restriction in the abnormal CTG group. These results may be due to a true lack of difference in obstetric intervention between women with normal or abnormal CTGs prior to induction of labour or more probably an inability to detect a difference in our small study. These baseline data allow the calculations necessary for a more substantive trial.

PACAP peptides modulate guinea pig cardiac neuron membrane excitability and neuropeptide expression

Morphological studies identified PACAP-immunoreactive nerve fibers in dense pericellular arrangements around virtually every cholinergic parasympathetic neuron of guinea pig cardiac ganglia; all postganglionic cardiac neurons expressed membrane-associated PAC1 receptor protein. Characterization of the alternative splice variants established predominant expression of the PAC1(very short) receptor transcript containing neither HIP nor HOP exons. PACAP depolarized cardiac neurons and increased membrane excitability; the excitability resulted from neither altered action potential properties nor inhibition of IM. Treatment of cardiac ganglia explants with PACAP significantly reduced the numbers of cholinergic neurons coexpressing somatostatin immunoreactivity, which did not appear to be correlated with prosomatostatin mRNA expression. The PACAP-mediated decrease in somatostatin immunoreactive neurons required calcium influx through L-type calcium channels and activation of adenylyl cyclase, whereas activation of phospholipase C or protein kinase A was not required. These observations indicate that PACAP through the PAC1 receptors elicits complex actions on guinea pig parasympathetic cardiac ganglia neurons, including modulation of membrane ion conductances and modulation of neuropeptide expression.

Regulation of parasympathetic neurons by mast cells and histamine in the guinea pig heart

The potential interaction between the immune system and the autonomic nervous system was examined in the cardiac ganglia of guinea pigs. Intracellular voltage recordings were used to determine the effects of mast cell degranulation on the membrane properties of parasympathetic neurons in animals actively sensitized to ovalbumin. Stimulation of mast cell degranulation by perfusion with ovalbumin (10 micrograms/ml) produced a depolarization and increase in the excitability of intracardiac neurons. These effects could be mimicked by histamine application, either by perfusion (10 microM) or by local pressure application (100 microM, 1-2 s application). In either case, histamine application resulted in a similar membrane depolarization and increase in excitability. Immunohistochemical experiments demonstrated that histamine-immunoreactive mast cells are located in close proximity to parasympathetic postganglionic neurons. The histamine response was not due to release of other neurotransmitters from adjacent nerve terminals and both the depolarization and increase in excitability were inhibited by the H1 antagonist, pyrilamine (300 nM), and were unaffected by the H2 antagonist cimetidine (5 microM). Incubation of cardiac ganglion preparations from sensitized animals with pyrilamine prior to ovalbumin perfusion resulted in the inhibition of both the depolarization and increase in excitability. These results demonstrate that mast cell degranulation, and the subsequent release of histamine, results in the stimulation of intracardiac neurons via the activation of H1 receptors. Thus, local inflammatory reactions in the cardiac tissue can lead to the rapid activation of parasympathetic neurons, thereby altering cardiac function.

NF-kappaB, p38 MAPK and JNK are highly expressed and active in the stroma of human colonic adenomatous polyps

The factors that govern the progression from colonic adenomatous polyp to colon cancer are poorly understood. The observation that NSAIDs act as chemopreventative agents and reduce the size of colonic polyps suggests the involvement of inflammatory signalling, but inflammatory signalling in colonic polyps has not been studied. We investigated the expression of the active forms of NF-kappaB, JNK and p38 MAPK using immunohistochemistry with activation specific antibodies in human colonic adenomas. We show that active NF-kappaB is seen in stromal macrophages that also express COX-2 and TNF-alpha, active JNK is seen in stromal and intraepithelial T-lymphocytes and periendothelial cells of new blood vessels, and active p38 MAPK is most highly expressed in macrophages and other stromal cells. These results demonstrate the presence of active inflammatory signal transduction in colonic polyps and that these are predominantly in the stroma. In the case of NF-kappaB this coincides with the cellular localisation of COX-2. These results support evidence that NSAIDs may act through effects on stromal cells rather than epithelial cells.

Pituitary adenylate cyclase-activating polypeptide innervation of the mudpuppy cardiac ganglion

The presence and potential origin of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) was determined in cardiac ganglia of the mudpuppy, Necturus maculosus. Although PACAP has been implicated in the regulation of cardiac function in several mammalian species, the presence of this peptide in the autonomic nervous system (ANS) of other species is unclear. Thus, this study is the first to characterize this highly conserved peptide in the ANS of a non-mammalian species. PACAP-immunoreactivity was observed in nerve fibers throughout the mudpuppy cardiac ganglia and often was co-localized with the sensory neuropeptides substance P and calcitonin gene-related peptide. Removal of all extrinsic inputs to the ganglia by organ culture eliminated PACAP-immunoreactivity in the cardiac ganglia, whereas bilateral vagotomies only partially reduced PACAP-labeling. PACAP-immunoreactive neurons were observed in both high thoracic dorsal root ganglia and in vagal sensory ganglia. While no PACAP-positive neurons were observed in caudal medulla brainstem regions, PACAP-containing nerve fibers were found in the region of the nucleus solitarius. These results suggest that, in the mudpuppy, PACAP is found primarily in visceral afferent fibers, originating from cells in either the dorsal root ganglia or vagal sensory ganglia. Based on their anatomic localization, these afferent fibers may function to transmit important sensory information to cardiovascular centers in the brain as well as serving as local reflex inputs to modulate postganglionic parasympathetic output within the cardiac ganglion itself.

Leptin signaling in human peripheral blood mononuclear cells, activation of p38 and p42/44 mitogen-activated protein (MAP) kinase and p70 S6 kinase

The adipocyte-derived hormone leptin plays an important role as a relayer of nutritional status to several organ systems. Evidence is accumulating that leptin plays an important role in the adequate functioning and maintenance of the immune system. Here we show that leptin induces sustained phosphorylation of p38 MAP kinase in human peripheral blood mononuclear cells (PBMCs). We show furthermore that leptin induces two routes to phosphorylation of the 40S ribosomal protein S6, one is activation of the p90 ribosomal S6 kinase (RSK) via the MEK/p42/p44 MAP kinase pathway, the other is via activation of p70 S6 kinase. Thus, these results give new insight in the mechanism that underlies the immunomodulatory effects of leptin.

Role of mitochondrial dysfunction in the Ca2+-induced decline of transmitter release at K+-depolarized motor neuron terminals

The present study tested whether a Ca2+-induced disruption of mitochondrial function was responsible for the decline in miniature endplate current (MEPC) frequency that occurs with nerve-muscle preparations maintained in a 35 mM potassium propionate (35 mM KP) solution containing elevated calcium. When the 35 mM KP contained control Ca2+ (1 mM), the MEPC frequency increased and remained elevated for many hours, and the mitochondria within twitch motor neuron terminals were similar in appearance to those in unstimulated terminals. All nerve terminals accumulated FM1-43 when the dye was present for the final 6 min of a 300-min exposure to 35 mM KP with control Ca2+. In contrast, when Ca2+ was increased to 3.6 mM in the 35 mM KP solution, the MEPC frequency initially reached frequencies >350 s-1 but then gradually fell approaching frequencies <50 s-1. A progressive swelling and eventual distortion of mitochondria within the twitch motor neuron terminals occurred during prolonged exposure to 35 mM KP with elevated Ca2+. After approximately 300 min in 35 mM KP with elevated Ca2+, only 58% of the twitch terminals accumulated FM1-43. The decline in MEPC frequency in 35 mM KP with elevated Ca2+ was less when 15 mM glucose was present or when preparations were pretreated with 10 microM oligomycin and then bathed in the 35 mM KP with glucose. When glucose was present, with or without oligomycin pretreatment, a greater percentage of twitch terminals accumulated FM1-43. However, the mitochondria in these preparations were still greatly swollen and distorted. We propose that prolonged depolarization of twitch motor neuron terminals by 35 mM KP with elevated Ca2+ produced a Ca2+-induced decrease in mitochondrial ATP production. Under these conditions, the cytosolic ATP/ADP ratio was decreased thereby compromising both transmitter release and refilling of recycled synaptic vesicles. The addition of glucose stimulated glycolysis which contributed to the maintenance of required ATP levels.

Mechanisms of pituitary adenylate cyclase activating polypeptide (PACAP)-induced depolarization of sympathetic superior cervical ganglion (SCG) neurons

Our understanding of PACAP expression and regulation of sympathetic neuronal function has been augmented considerably over the last few years. Among the three major VIP/PACAP receptor subtypes, the SCG appears to express preferentially one particular variant of the PACAP-selective PACAP1 receptor coupled to multiple intracellular signaling cascades. The in situ histochemical hybridization and immunocytochemical studies of PACAP1 receptor mRNA and protein are in good agreement; nearly all of the SCG neurons express the PACAP-selective receptor, suggesting that most of the sympathetic neurons are under PACAP neuromodulation. In accord with that possibility, several independent studies have now demonstrated PACAP peptide expression in the IML sympathetic preganglionic neurons and fibers, including those projecting to the SCG, further emphasizing the significance of PACAP peptides as a preganglionic noncholinergic mediator of sympathetic function. Given the high potency of PACAP on any of a number of cellular responses, the functional relevance of PACAP peptides on SCG neurons is considerable. We have previously demonstrated the potency and efficacy of both PACAP27 and PACAP38 on sympathetic neuron neurotransmitter/neuropeptide production and secretion; the ability of these peptides to stimulate neuronal second messenger activation was also in the nanomolar range. These results are congruous with our current electrophysiological studies, which were driven to further define the dynamic sympathetic responses to PACAP. In line with the morphological studies, for example, more than 90% of the sympathetic neurons responded to PACAP. In agreement with previous neuropharmacological data, the PACAP-induced depolarizations were elicited at physiologically relevant peptide concentrations at high affinity PACAP-selective receptors. The effects were direct and the alterations in postganglionic neuronal membrane properties appeared to be mediated by several ionic mechanisms. If these studies were analogous to pieces in a puzzle to understand the effects of PACAP in sympathetic development and function, the picture of late has been more completely assembled. But several important challenges still remain. What are the signal transduction mechanisms that mediate the PACAP-induced changes in sympathetic membrane properties? How do the resulting alterations impact the acute and more long-term responses of sympathetic neurons? Does the coupling of PACAP1 receptors to intracellular signaling pathways differ during development, resulting in a transition from the neurotrophic properties of PACAP in neuroblasts to neuromodulatory roles of the peptides in postmitotic neurons? By looking at these issues in one distinct neuronal system, we enlarge our understanding and appreciation of peptides, and PACAP in particular, in the molecular and cellular events guiding neuronal development, function, and plasticity.

Pituitary adenylate cyclase-activating polypeptide expression and modulation of neuronal excitability in guinea pig cardiac ganglia

Cardiac output is regulated by the coordinate interactions of stimulatory sympathetic and inhibitory parasympathetic signals. Intracardiac parasympathetic ganglia are integrative centers of cardiac regulation, and modulation of the parasympathetic drive on the heart is accomplished by altering intrinsic cardiac ganglion neuron excitability. The pituitary adenylate cyclase-activating polypeptide (PACAP)/vasoactive intestinal peptide (VIP) family of peptides modulates cardiac function, and in guinea pig heart, PACAP appears to act directly on intrinsic parasympathetic cardiac ganglia neurons through PACAP-selective receptors. A multidisciplinary project tested whether cardiac PACAP peptides act through PACAP-selective receptors as excitatory neuromodulators amplifying the parasympathetic inhibition from guinea pig cardiac ganglia. The in vivo sources of regulatory PACAP peptides were localized immunocytochemically to neuronal fibers and a subpopulation of intrinsic postganglionic cardiac neurons. RT-PCR confirmed that cardiac ganglia expressed proPACAP transcripts and have PACAP peptide biosynthetic capabilities. Messenger RNA encoding PACAP-selective PAC1 receptor isoforms were also present in cardiac ganglia. Alternative splicing of PAC1 receptor transcripts produced predominant expression of the very short variant with neither HIP nor HOP cassettes; lower levels of the PAC1HOP2 receptor mRNA were present. Almost all of the parasympathetic neurons expressed membrane-associated PAC1 receptor proteins, localized immunocytochemically, which correlated with the population of cells that responded physiologically to PACAP peptides. PACAP depolarized cardiac ganglia neurons and increased neuronal membrane excitability. The rank order of peptide potency on membrane excitability in response to depolarizing currents was PACAP27>PACAP38>VIP. The PACAP-induced increase in excitability was not a function of membrane depolarization nor was it caused by alterations in action potential configuration. These results support roles for PACAP peptides as integrative modulators amplifying, through PACAP-selective receptors, the parasympathetic cardiac ganglia inhibition of cardiac output.

Expression and physiological actions of neuropeptide Y in guinea pig parasympathetic cardiac ganglia

Guinea pig atrial whole mount preparations containing the parasympathetic cardiac ganglia were used to establish the expression, distribution and actions of neuropeptide Y (NPY) in atrial tissues. NPY-immunoreactive fibers densely innervated the atrial myocardium and blood vessels. Fibers containing NPY also innervated intrinsic parasympathetic cardiac neurons. Four percent of the cardiac neurons, identified using microtubule associated protein-2 antiserum, were NPY-positive. An endogenous source of NPY was confirmed with reverse transcription PCR which demonstrated the presence of proNPY mRNA. Sixty percent of the parasympathetic cardiac neurons were hyperpolarized by local application of NPY. NPY also decreased the amplitude and duration of the action potential after hyperpolarization in 60% of the neurons and decreased the fast excitatory postsynaptic potential in about 50% of the cells. These observations indicate that NPY is anatomically positioned to directly alter the output of the parasympathetic cardiac ganglia either by hyperpolarizing the cardiac neurons or by decreasing the fast synaptic input which drives individual neurons.

Tachykinin-induced activation of non-specific cation conductance via NK3 neurokinin receptors in guinea-pig intracardiac neurones

1. Whole mount preparations from guinea-pig hearts were used to characterize the receptors and ionic mechanisms mediating the substance P (SP)-induced depolarization of parasympathetic postganglionic neurones of the cardiac ganglion. 2. Measurement of the amplitude of depolarization in response to superfusion of different tachykinin agonists (neurokinins A (NKA) and B (NKB), SP, and senktide) gave a rank-order potency of NKB = senktide > NKA > SP, indicating involvement of an NK3 receptor. The use of the selective tachykinin receptor antagonists SR 140333, SR 48986, and SR 142801 demonstrated that only the NK3 receptor antagonist SR 142801 inhibited the SP-induced depolarization. 3. The SP-induced depolarization was not inhibited by Ba2+, TEA, or niflumic acid, or altered by reduced Cl- solutions, but was attenuated in reduced Na+ solutions. Single electrode voltage clamp studies demonstrated that the SP-induced inward current increased in amplitude at more negative potentials, had a reversal potential of approximately 0 mV, and was reduced in amplitude in reduced Na+ solutions. 4. We conclude that the SP-induced depolarization in guinea-pig postganglionic parasympathetic neurones of the cardiac ganglion is due to NK3-mediated activation of a non-selective cation conductance.

Transmitter release differs at snake twitch and tonic endplates during potassium-induced nerve terminal depolarization

Twitch and tonic muscle fibers of snake skeletal muscle differ in their synpatic as well as mechanical properties. These experiments were aimed at detemining the basis of the difference in vesicular release properties of nerve terminals at twitch and tonic endplates. Miniature endplate currents (MEPCs) were recorded from voltage-clamped garter snake muscle fibers depolarized by high K+ in either a control Ca2+ or high-Ca2+ solution. MEPC frequency increased at twitch and tonic endplates and remained elevated for 8 h during depolarization in control Ca2+. At twitch endplates depolarized in the presence of high Ca2+, an increase in MEPC frequency was followed by a progressive decline. In contrast, MEPC frequency remained elevated in high Ca2+ at tonic endplates. The observed decrease in MEPC frequency at depolarized twitch endplates in high Ca2+ was not a function of the level of depolarization or initial MEPC frequency, nor was it due to a reduction in MEPC amplitude and loss of MEPCs in baseline noise. An optical assay of presynaptic function in which the activity-dependent dye FM1-43 was used confirmed that quantal releases differs at twitch and tonic endplates. Most twitch nerve terminals were labeled by FM1-43 during prolonged depolarization with control Ca2+ or after brief depolarization with high Ca2+. In contrast, the number of twitch nerve terminals and the degree to which they were stained was greatly reduced after prolonged exposure to high K+ and high Ca2+, whereas depolarized tonic endplates were well stained by FM1-43 during brief and prolonged exposure to high Ca2+. FM1-43 staining also revealed variable levels of quantal release between individual boutons at twitch endplates after prolonged depolarization in high-Ca2+ solution. The observed reduction in presynaptic function at twitch nerve terminals after prolonged depolarization in high-Ca2+ solution was reversible and therefore not due to irreversible damage to terminal boutons. MEPC frequency increased at both twitch and tonic endplates when either Sr2+ or Ba2+ was substituted for high Ca2+ during K(+)-induced depolarization. Over time, in Sr2+ or Ba2+ solutions, MEPC frequency remained elevated at tonic endplates but declined at twitch endplates with a time course similar to that observed in high Ca2+. MEPC amplitudes at both endplates remained constant. We conclude that the regulation of quantal release differs in nerve terminals innervating twitch and tonic endplates and postulate that differential intraterminal accumulation of Ca2+ may underlie the observed difference in presynaptic function.

Activation of the protein phosphatase calcineurin during carbachol exposure decreases the extent of recovery from end-plate desensitization

1. Our previous studies demonstrated that protein kinase C (PKC) activity is required for acetylcholine (ACh) sensitivity to recover fully at snake twitch fiber end plates after prolonged exposure to carbachol. In the present studies, we have investigated whether protein phosphatase(s), activated during carbachol exposure, dephosphorylated critical membrane proteins, which required rephosphorylation by PKC to maintain end-plate sensitivity. End-plate sensitivity was assessed from measurements of miniature end-plate currents (MEPCs) and carbachol-activated currents (EPCCARBS). Conductance of ACh-activated channels was determined from patch-clamp recordings of single-channel currents. 2. Pretreatment of snake muscle preparations with the protein kinase inhibitor staurosporine (0.5 microM), followed by a 10-min exposure to 540 microM carbachol, reduced mean MEPC amplitudes to values 30-40% less than those recorded before carbachol exposure. Conversely, at control end plates exposed to carbachol, the mean MEPC amplitude was reduced by only approximately 5% compared with precarbachol values. This staurosporine-induced decrease in ACh sensitivity could be prevented by pretreatment with the protein phosphatase 2B (calcineurin) inhibitor deltamethrin (0.5 microM), whereas okadaic acid (5 microM) and calyculin A (0.5 microM), inhibitors of protein phosphatases 1 and 2A, had no effect. 3. After a 10-min exposure to 540 microM carbachol, EPCCARB amplitudes (produced by local superfusion with 20 microM carbachol) were significantly smaller at staurosporine-treated end plates than at control end plates. In contrast, the EPCCARB amplitude recorded from end plates pretreated with both deltamethrin and staurosporine was not significantly different from that recorded at control end plates. 4. Substitution of 10 mM Mn2+ for external Ca2+ during the exposure to 540 microM carbachol prevented the decrease in MEPC amplitude recovery at staurosporine-treated end plates. These results suggested that the alteration in sensitivity at staurosporine-treated end plates was calcium dependent. 5. At control end plates, a single population of ACh-activated channels (45-50 pS) is observed both before and after a 10-min exposure to 540 microM carbachol. Conversely, at staurosporine-treated end plates, after exposure to carbachol, a second population of small-conductance (25-30 pS) ACh-activated channels is present in addition to the predominant 45- to 50-pS ACh-activated channels. In preparations pretreated with both deltamethrin and staurosporine, after carbachol exposure, there was a significant decrease in the frequency of small-conductance ACh-activated channels. Deltamethrin treatment alone produced no small-conductance channels before or after a 10-min exposure to 540 microM carbachol. Also, no small-conductance ACh-gated channels were recorded at PKC-inhibited end plates after carbachol exposure either with pretreatment with 10 microM cyclosporin A (another inhibitor of calcineurin) or with the substitution of 10 mM Mn2+ for Ca2+ during the 10-min agonist exposure. 6. We propose that during prolonged exposure to the nicotinic agonist carbachol, calcium influx through ACh-gated channels elevates the level of ionized calcium at the inner surface of the post-junctional membrane and that this local rise in intracellular calcium activates the calcium-dependent phosphatase calcineurin. Dephosphorylation of some key membrane protein by calcineurin leads to a decrease in the extent of recovery from desensitization. Under normal conditions, this process is effectively reversed by PKC activity and end-plate sensitivity recovers fully. However, when PKC is inhibited, the extent of recovery of end-plate sensitivity is decreased, and associated with this decrease is the presence of small-conductance ACh-activated channels not normally recorded at snake twitch fiber end plates.

Evidence for afferent fiber innervation of parasympathetic neurons of the guinea-pig cardiac ganglion

The present study was done to establish whether peptidergic afferent inputs can modulate parasympathetic neurons of the guinea-pig cardiac ganglion. Whole mount preparations from the guinea-pig heart were utilized to localize afferent terminals by immunohistochemistry and for intracellular recordings from individual neurons in situ. Action potentials could be elicited by both intracellular current injection and stimulation of interganglionic fiber bundles. Two types of neuron, phasic (95%) and tonic (5%) as defined by their firing properties, were observed. High frequency (5-10 Hz) interganglionic fiber stimulation produced a calcium-dependent, slow depolarization in many cells which was not blocked by 100 microM hexamethonium or 1 microM atropine. A prolonged depolarization was also produced by local application of capsaicin (1 mM), which releases substance P and CGRP from afferent nerve terminals. Microinjection of the mammalian tachykinins substance P, neurokinin A and neurokinin B (all at 100 microM), also produced a slow depolarization. Application of specific agonists for the tachykinin receptor subtypes indicated that these neurons express both NK2 and NK3 receptors. Individual cells were filled with neurobiotin to examine their morphology and the preparations were counter-stained for SP-like immunoreactivity. The results demonstrated that SP-positive fibers are found in close apposition to both phasic and tonic neurons. From these results, we suggest that the parasympathetic neurons of the guinea-pig cardiac ganglion receive inputs from peptidergic, afferent fibers and that this input provides a pathway for potential local reflex control of cardiac function.

Necessity of protein kinase C activity for maintenance of acetylcholine receptor function at snake twitch fibre endplates

1. The extent of recovery of endplate sensitivity following a 5 or 10 min exposure to carbachol was determined from measurements of miniature endplate current (m.e.p.c.) amplitudes in voltage-clamped snake twitch fibre endplates. M.e.p.c. amplitude recovery was dependent on the carbachol concentration (0.27-5.4 mM) and duration of application. Staurosporine pretreatment (0.5 microM for approximately 15 min) further decreased the extent of m.e.p.c. amplitude recovery. 2. The decrease in m.e.p.c. amplitude at control endplates exposed to high concentrations of agonist (5.4 mM carbachol for 10 min) was due to an apparent decrease in postsynaptic receptor density, not to a change in the conductance of the acetylcholine (ACh)-activated channels. 3. Pretreatment with either 1 microM lavendustin A or 50 microM KN-62 had no effect on m.e.p.c. amplitude recovery, whereas pretreatment with either 0.5 microM staurosporine, 50 microM sphingosine, or 0.5 microM calphostin C significantly reduced m.e.p.c. amplitude recovery following carbachol exposure. 4. Sphingosine and staurosporine produced a concentration-dependent decrease in the extent of m.e.p.c. amplitude recovery, but had no effect on m.e.p.c. characteristics in the absence of carbachol. In addition, this decrease in m.e.p.c. amplitude was not due to the presence of a subpopulation of small amplitude m.e.p.cs. 5. Prolonged treatment (18-20 h) of muscles with 200 nM phorbol 12-myristate 13-acetate (PMA), to down regulate protein kinase C, resulted in a significant reduction in m.e.p.c. amplitudes following exposure to carbachol. Conversely, treatment with 200 nM 4 alpha PMA, an inactive analogue, had no effect on m.e.p.c. amplitude recovery. 6. Only large amplitude ACh-activated channels (~50 pS) were recorded from fibres either in the presence of 50 micro M sphingosine or from fibres chronically exposed to PMA. However, following recovery from a 10 min exposure to 540 micro M carbachol, both small conductance (-25 pS) and large conductance ACh-activated channels were recorded in both sphingosine- and phorbol-treated preparations. The conductance of these two populations of channels was virtually identical to those seen in staurosporine treated fibres following carbachol exposure.7. We conclude that protein kinase C is required for full recovery of AChR sensitivity following carbachol-induced receptor inactivation. Exposure to high concentrations of agonist for prolonged periods appears to result in the inactivation of a subpopulation of receptors. These receptors must be replaced or reactivated by a process involving protein kinase C. When this phosphorylation step is inhibited, the AChRs remain in an activatable form, but with a reduced conductance.

Requirement of a colchicine-sensitive component of the cytoskeleton for acetylcholine receptor recovery

1. The effect of colchicine treatment on acetylcholine receptor function was examined in potassium depolarized, voltage-clamped snake twitch fibre endplates. Receptor function was assessed by analysis of miniature endplate currents (m.e.p.c.) as well as acetylcholine (ACh)-induced single channel currents. 2. Pretreatment of snake muscle fibres with colchicine (10 microM to 100 microM) for 16-18 h had no effect on m.e.p.c. amplitude or decay rates. At higher concentrations (1 mM), there was a slight decrease in the average m.e.p.c. amplitude. 3. Colchicine produced a concentration-dependent decrease in the extent of m.e.p.c. amplitude recovery following a 10 min exposure to 540 microM carbachol. Exposure of 100 microM colchicine-treated preparations to 0.5 microM staurosporine further reduced the extent of m.e.p.c. amplitude recovery following carbachol exposure. 4. The decrease in m.e.p.c. amplitude following carbachol exposure was not due to a shift in the m.e.p.c. reversal potential. In addition, the distribution of m.e.p.c. amplitudes remained unimodal in both control and colchicine (100 microM)-treated preparations following carbachol exposure. 5. In addition to the normal, large conductance (approximately 48 pS) ACh-activated channels, a population of small conductance (approximately 29 pS) channels was observed in colchicine-treated preparations following exposure to carbachol. In preparations treated with both colchicine and staurosporine and then exposed to carbachol, the conductance of these small channels was identical to that of colchicine or staurosporine alone. 6. We suggest that prolonged exposure of snake twitch fibre endplates to agonist results in the activation and desensitization of ACh receptors. Furthermore, we propose that for a subpopulation of the inactivated receptors, restoration of function requires both the integrity of a subsynaptic cytoskeletal component and phosphorylation by a staurosporine-sensitive protein kinase. One plausible mechanism is that some receptors become destabilized in the membrane and phosphorylation of a cytoskeletal component, whose distribution may depend on an intact microtubular system, is required to re-anchor these receptors. If this anchoring process is inhibited either by disruption of the cytoskeleton with colchicine, or inhibition of the kinase by staurosporine, these receptors remain activatable, but have a reduced conductance.

Necessity of divalent cations for recovery from carbachol-induced nicotinic acetylcholine receptor inactivation at snake twitch fibre endplates

1. Previous studies demonstrated that elevation of the extracellular calcium concentration during a prolonged exposure to a high concentration of carbachol reverses the staurosporine-induced decrease in the extent of endplate resensitization in voltage-clamped snake twitch fibres. The present studies were designed to establish the site, specificity and potential mechanisms by which calcium could reverse the effects of staurosporine on acetylcholine receptor recovery. 2. Pretreatment of potassium-depolarized muscle preparations with 0.5 microM staurosporine, followed by a 10 min incubation with 540 microM carbachol, produced a significant decrease in the recovery of miniature endplate current (m.e.p.c.) amplitudes. Raising the extracellular calcium concentration from 1 mM to 10 mM during the agonist application reversed this inhibition. In addition, a brief (3 min) incubation in an elevated calcium (10 mM) solution in staurosporine-treated preparations previously exposed to 540 microM carbachol also reversed the reduction in m.e.p.c. amplitude. 3. Substitution of calcium with 10 mM strontium had no effect on the staurosporine-induced decrease in m.e.p.c. amplitude, whereas 10 mM magnesium partially substituted for calcium. Inclusion of (+)-tubocurarine (13 microM) in the 10 mM calcium solution to prevent the influx of calcium through agonist-activated channels did not prevent the reversal of the staurosporine-induced decrease in m.e.p.c. amplitudes. This suggested that the site of action of calcium on endplate resensitization was extracellular. 4. Analysis of acetylcholine (ACh)-induced single channel currents demonstrated that a population of small conductance channels seen only in the staurosporine-treated preparations following carbachol exposure, was still present in staurosporine-treated preparations incubated in 540 microM carbachol solution containing 10 mM calcium. Thus the effect of calcium on ACh receptor recovery was not due to the conversion of the small conductance channels to the normal, large conductance channels.5. Removal of calcium from the extracellular solution with the magnesium concentration unchanged,resulted in no change in the extent of m.e.p.c. amplitude recovery, nor did it alter the ability of staurosporine to inhibit recovery. Removal of both calcium and magnesium resulted in a significant decrease in the extent of recovery and staurosporine produced no additional decrease. This decrease in m.e.p.c. recovery in the divalent cation-free solution was not associated with a change in mean channel conductance as determined by noise analysis.6. Based on the results from these experiments, we suggest that, with prolonged exposure to agonist,some ACh receptors at the endplate become irreversibly inactivated. For full recovery of endplate sensitivity to occur, inactivated ACh receptors must be replaced. Part of the replacement ACh receptors appear to be recruited from a readily available but not previously activated pool and this process is dependent on extracellular calcium and/or magnesium. Thus, elevation of extracellular calcium may be able to reverse the apparent decrease in endplate sensitivity in staurosporine-treated fibres following carbachol exposure by increasing the number of functional receptors at the endplate.

Quantal transmitter release at snake twitch and tonic muscle fibres during prolonged nerve terminal depolarization

1. Miniature endplate currents (MEPCs) were recorded in vitro from voltage-clamped twitch and tonic muscle fibres in costocutaneous muscles of the garter snake, Thamnophis. Recordings were made from fibres in a control sodium-containing solution and then during exposure to an isotonic potassium solution containing either 1.0 mM calcium and 4.2 mM magnesium or 3.6 mM calcium. The experiments were done at two levels of external calcium in order to demonstrate that the change in MEPC frequency was calcium dependent. During the initial exposure to the isotonic potassium solutions, the MEPC frequency was increased manyfold at both twitch and tonic fibres, but it declined progressively with continued exposure. MEPCs were recorded from both fibre types throughout a 20 h exposure to the isotonic potassium solution with 1 mM calcium, but no MEPCs were recorded at most twitch endplates after approximately 6 h in the isotonic potassium solution containing 3.6 mM calcium. In contrast, MEPCs were still present at tonic fibre endplates after 20 h in the isotonic potassium solution containing 3.6 mM calcium. 2. After 30 min in the isotonic potassium solution with 1 mM calcium, the MEPC amplitude recorded from both fibre types was approximately twice that in the control sodium-containing solution. At tonic endplates, the MEPC amplitude was also twofold greater in the isotonic potassium solution with 3.6 mM calcium than in sodium-containing solution. In contrast, after 30 min in the isotonic potassium solution containing 3.6 mM calcium, the MEPC amplitude at twitch endplates was similar to that in control solution. 3. In both fibre types, MEPC amplitude decreased progressively with continued exposure to the isotonic potassium solutions. The progressive decrease in MEPC amplitude was not due to a gradual decrease in postsynaptic sensitivity to acetylcholine. 4. The effects of high potassium were reversible as MEPCs were recorded at twitch fibre endplates in preparations which were returned to the control sodium-containing solution after a 20 h exposure to the isotonic potassium solution containing 3.6 mM calcium. 5. Ultrastructural examination showed that after a 6 h exposure to the isotonic potassium solutions most nerve terminals innervating twitch fibre endplates were devoid of synaptic vesicles whereas at the same time many synaptic vesicles were present in nerve terminals innervating tonic fibre endplates. Surprisingly, numerous synaptic vesicles were present in nerve terminals innervating either fibre type in muscle preparations exposed to the isotonic potassium solutions for 20 h.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of staurosporine-induced decrease in acetylcholine receptor recovery from desensitization

1. Previously, we showed in voltage-clamped snake twitch muscle fibres that the extent of recovery of the nicotinic acetylcholine (ACh) receptor from carbachol-induced desensitization is reduced by pretreatment with the protein kinase inhibitor staurosporine. The present studies were undertaken to determine the mechanism underlying the staurosporine-induced inhibition of recovery. 2. Pretreatment with 0.5 microM staurosporine significantly decreased the extent of recovery of spontaneous miniature endplate current (m.e.p.c.) amplitudes in preparations exposed to 540 microM carbachol. The decrease in recovery of m.e.p.c. amplitude by staurosporine was dependent on the duration of carbachol exposure. No significant decrease in m.e.p.c. amplitude was observed with a 1 min exposure to agonist, whereas a significant decrease in recovery was seen with agonist exposures between 5-10 min. Further, the effect of staurosporine pretreatment on ACh receptor recovery was long-lasting such that m.e.p.c. amplitude remained decreased for at least 60 min. 3. Estimation of mean channel conductance by noise analysis during local perfusion of 20 microM carbachol demonstrated a decrease in conductance from 52 pS to 23 pS in staurosporine-treated preparations following recovery from desensitization. Staurosporine treatment in the absence of desensitization did not alter the mean channel conductance. 4. A single population of ACh-activated single channel currents with a conductance of 45-49 pS was recorded in cell-attached patches from enzymatically cleaned endplates in control and staurosporine-treated preparations not exposed to carbachol. 5. At staurosporine-treated endplates exposed to carbachol and then allowed to recover, a population of small conductance (23 pS) channels was observed. These channels were not normally seen in control preparations which had undergone carbachol-induced desensitization and recovery.6. We suggest that the decrease in m.e.p.c. amplitude observed following recovery from desensitization in staurosporine-treated endplates results from the activation of a mixture of small and large conductance ACh receptor channels.

Galanin stimulates phosphatidylinositol turnover in cardiac tissue of the mudpuppy

A galanin-like peptide has been found in the parasympathetic fibers innervating the mudpuppy myocardium and direct application of galanin produces hyperpolarization of atrial myocytes and a decrease in twitch tension. In the present study, atrial and ventricular strips were incubated with galanin and then evaluated for changes in either phosphatidylinositol turnover or cyclic nucleotide levels. Galanin caused a significant and concentration-dependent increase in phosphatidylinositol turnover in both atrial and ventricular tissue. However, galanin had no effect on cyclic AMP or cyclic GMP levels in either basal or adrenergically-stimulated preparations. These results suggest that the galanin-induced cardio-inhibition in the mudpuppy may be mediated, at least in part, by a change in phosphatidylinositol turnover.

Aminergic and peptidergic elements and actions in a cardiac parasympathetic ganglion

Correlated histochemical, immunocytochemical, and electrophysiological experiments have been undertaken to identify putative neurotransmitter-neuromodulator substances in cells and fibers in the parasympathetic cardiac ganglion of the mudpuppy, Necturus maculosus, and to determine the action of these agents on the properties of the parasympathetic postganglionic neurons. The mudpuppy cardiac ganglion contains two neuron types: large parasympathetic postganglionic neurons and smaller intrinsic neurons initially identified as small intensely fluorescent cells. We have shown that the postganglionic neurons contain both acetylcholine and a galanin-like neuropeptide. Also, we have demonstrated that the intrinsic neurons contain a number of different biogenic amines such as dopamine and serotonin, as well as neuropeptides including a substance P-like peptide and a galanin-like peptide. The results of these studies indicate that the anatomical and histochemical organization of the mudpuppy cardiac ganglion is more complex than that seen in other amphibians and is very similar to that found in most mammalian species. Previously, we showed that galanin has actions that make it of interest as a potential inhibitory neurotransmitter in the mudpuppy cardiac ganglion. Galanin hyperpolarizes and decreases membrane excitability in most parasympathetic neurons. Here we show that galanin initiates membrane hyperpolarization by activating a voltage- and time-dependent potassium conductance. We also present the initial results of ongoing studies which indicate that calcitonin gene-related peptide can depolarize some of the parasympathetic neurons as well as evidence that serotonin initiates depolarization in many parasympathetic neurons. This serotonin-induced depolarization consists of an initial transient depolarization followed by a longer, more slowly developing depolarization. Action potential activity is stimulated during the initial period of depolarization, but depressed during the later, slow depolarization. The results of these electrophysiological experiments suggest that many of the bioactive substances that have been identified in the different cells and nerve fibers within the cardiac ganglion affect the excitability of the postganglionic neurons. In conclusion, we suggest that the results of the studies summarized in this review demonstrate that the cardiac ganglion in the mudpuppy is not simply a relay station. Rather, the cardiac ganglion has a complex organization and exhibits a diversity of physiological responses, indicating that it very likely is another site of integration for control of cardiac function.

Staurosporine inhibits the extent of acetylcholine receptor recovery from carbachol-induced desensitization in snake twitch fibres

1. The effect of the protein kinase inhibitor, staurosporine, on the extent and time course of recovery following carbachol-induced desensitization was studied in snake twitch-muscle fibres maintained in an isotonic potassium propionate solution and voltage-clamped to +30 mV. 2. Pretreatment with staurosporine (0.5 microM) decreased the extent of recovery of spontaneous miniature endplate current (m.e.p.c.) amplitudes following desensitization by a sustained application of 540 microM carbachol. Recovery was inhibited by approximately 50% without altering the time course of m.e.p.c. recovery. 3. Staurosporine also produced a concentration-dependent (10 nM to 0.5 microM) decrease in the amplitude of a second carbachol-induced current, following a wash period, as compared to the amplitude of the current produced by the initial carbachol application. Pretreatment with 0.5 microM K252a, another wide spectrum protein kinase inhibitor, also decreased the extent of recovery of the response to a second carbachol application following desensitization. 4. Staurosporine pretreatment (0.5 microM) had no effect on either the kinetics of receptor-channel gating or the initial endplate sensitivity to agonist. This was determined by comparing the amplitude of the carbachol (540 microM)-induced currents and the amplitude and decay rate of m.e.p.cs in control and staurosporine-treated fibres. 5. Staurosporine had no effect on the time course of desensitization onset produced during the initial application of 540 microM carbachol or the depth of desensitization produced by the end of a 2-3 min exposure to 540 microM carbachol.6. Elevation of the external calcium concentration from 1 to 10mM during the 540 microM carbachol application completely antagonized the decreased extent of recovery of m.e.p.c. amplitude produced by pretreatment with 0.5 microM staurosporine.7. We suggest that phosphorylation of a population of acetylcholine receptors is required for complete recovery from desensitization, and that staurosporine inhibits the protein kinases responsible for this phosphorylation.8. We further propose that a transient increase in intracellular calcium, produced by an increase in calcium influx through agonist-activated endplate channels, stimulates additional protein kinase activity, which in turn, antagonizes the effect of staurosporine-treatment on recovery.

Extracellular ATP stimulates norepinephrine uptake in PC12 cells

This study examined the effects of extracellular ATP on norepinephrine (NE) uptake, using PC12 cells as a model of noradrenergic neurons. Previous experiments with synaptosomes led to the hypothesis that extracellular ATP can regulate NE uptake via an ecto-protein kinase. In the present study, we examined the high-affinity uptake of NE (referred to as uptake 1) in PC12 cells in the presence of varying concentrations of extracellular ATP. In the presence of Ca2+, low concentrations of ATP (0.1 microM) increased uptake 1 by approximately 36%. This increase could be mimicked by adenosine-5'-O-(3-thiotriphosphate) tetralithium salt (ATP gamma S), an analogue of ATP which can be utilized by protein kinases, and not by 5'-adenylylimidodiphosphate tetralithium salt, a nonhydrolyzable analogue of ATP, GTP, ADP, and adenosine also had no effect on uptake 1. Preincubation of the cells with NE and ATP gamma S, followed by washing and assaying NE uptake 30 min later, resulted in a persistent increase in uptake 1. Similar pretreatment with ATP did not show this increase; however, simultaneous pretreatment with ATP and ATP gamma S blocked the activation produced by ATP gamma S alone. Kinetic analysis showed that ATP gamma S pretreatment produces an increase in the Vmax of uptake 1 without altering the apparent Km for NE. These results support the hypothesis that extracellular ATP can regulate NE uptake via an ecto-protein kinase.