Patent foramen ovale (PFO) and migraine: role of platelet Tissue Factor expression and oxidative stress. The LEARNER study

Background

Migraine is a chronic neurovascular disorder with a multifactorial aetiology. A strong relationship links migraine with aura (MHA) and patent foramen ovale (PFO), with migraine regression after PFO closure. Increased platelet aggregation and oxidative stress were documented in migraineurs. Current guidelines suggest the use of aspirin or P2Y12-antagonists. To date, however, no clear mechanisms connecting MHA to PFO has been demonstrated.

Purpose

To perform a comprehensive analysis of platelet activation, inflammation and oxidative stress status in 78 aspirin-treated MHA-patients before (T0) and 6-months after (T1) PFO closure (LEARNER Study-NCT03521193-clinicaltrials.gov). Primary endpoint was migraine regression rate in relation to these parameters.

Methods

P-selectinpos-, activated-glycoproteinIIbIIIa (aGPIIbIIIa)pos-, Tissue Factor (TF)pos-, reactive oxygen species (ROS)pos-platelets, platelet-leukocyte aggregates (PLA) and microvesicles (MVs) were evaluated by flow cytometry; thrombin generation (TG) by Calibrated Automated Thrombogram (CAT) assay; oxidative stress status by mass spectrometry. Twelve aspirin-treated-healthy subjects (HS) were enrolled for comparison. To test the effect of PFO patients' plasma on platelet activation, blood from HS was plasma-depleted and replaced with a pool of plasma from PFO patients.

Results

Migraine resolution occurred in 69.7%, significant reduction in 27%, while no effect was observed in 2 patients (3.2%). Only ROSpos-platelets, and TFpos-platelets and -MVs were significantly higher at T0, sustaining a TG capacity that was associated with an altered blood GSSG/GSH (Oxidized/Reduced Glutathione) ratio. This phenotype reverted to HS levels at T1 (Fig. 1). MHA-PFO plasma, added to HS blood, mirrored the in vivo platelet activation and N-acetylcysteine blunted it. In vitro GSSG treatment of HS platelets reproduced the in vivo condition. Aspirin had little effect on the platelet prothrombotic phenotype which was effectively inhibited by a P2Y12-antagonist (Fig.2).

Conclusions

MHA-PFO patients show a platelet-associated prothrombotic phenotype, characterized by a marked thrombin generation capacity sustained by an elevated number of platelets and MVs expressing a functionally active Tissue Factor and sustained by altered oxidative stress status. This phenotype, not fully controlled by aspirin but by P2Y12-antagonism, reverted after PFO closure together with a complete migraine remission.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Italian Ministry of Health

Long COVID-19 syndrome: association of cardiopulmonary impairment with a persistent platelet activation

Background

A considerable proportion of patients do not fully recover from COVID-19 infection and report symptoms that persist beyond the initial phase of infection: this condition is defined long-COVID-19 syndrome (LCS). LCS can involve lungs as well as several extrapulmonary organs, including the cardiovascular system. The risk and 1-year burden of cardiovascular diseases (CVD) is increased in COVID-19 survivors, even in subjects at low risk of CVD. Recently, we documented that acute COVID-19 infection induces altered platelet activation state characterized by a prothrombotic phenotype and by the formation of platelet-leukocyte aggregates (PLA), that may be involved in the pulmonary microthrombi found in autoptic specimens. No data are yet available on the contribution of platelet activation to residual pulmonary impairment and procoagulant potential in LCS patients.

Purpose

To study platelet activation status, microvesicle (MV) profile, platelet thrombin generation capacity (pTGC) in LCS patients enrolled at 6 months after resolution of the acute phase (6mo-FU), compared to acute COVID-19 infection patients.

Methods

6mo-FU COVID-19 patients (n=24) with established LCS were enrolled at Centro Cardiologico Monzino. Residual pulmonary impairment was assessed by Cardiopulmonary Exercise Testing (CPET) and 64-rows-CT scan evaluation. Platelet activation (P-selectin, Tissue Factor [TF] and PLA) and MV profile were assessed by flow cytometry; pTGC by calibrated automated thrombogram. 46 patients enrolled during acute COVID-19 infection and 46 healthy subjects (HS) were used for comparison.

Results

Dispnea in LCS patients was confirmed by CPET showing compromised alveolus-capillary membrane diffusion and residual pulmonary impairment. TF+-platelet and -MV levels were 3-fold (1.5% [1.2–2.9] vs 2.4% [1.6–5.7]) and 2-fold (217/μl [137–275] vs 435/μl [275–633]) lower at 6mo-FU compared to acute phase, being comparable to HS. pTGC behaved similarly. At 6mo-FU, the MV profile, in terms of total number and cell origin, returned to physiological levels. Conversely, although lower than that measured in acute phase, a 2.5-fold higher platelet P-selectin expression (6.9% [3–13.5] vs 11.7% [5.2–18.9]) and PLA formation (35.5% [27.4–46.8] vs 67.7% [45.7–85.3]) was observed at 6mo-FU compared to HS. Interestingly, a significant correlation between PLA formation and residual pulmonary impairment was observed (r=−0.423; p=0.02).

Conclusion

These data strengthen the hypothesis that the presence of PLA in the bloodstream, and thus also in the pulmonary microcirculation, may contribute to support pulmonary dysfunction still observed in LCS patients.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Italian Ministry of Health (Ricerca Corrente 2020 MPP COVID4)

Targeting ion channels in cancer: a novel frontier in antineoplastic therapy

Targeted therapy is considerably changing the treatment and prognosis of cancer. Progressive understanding of the molecular mechanisms that regulate the establishment and progression of different tumors is leading to ever more specific and efficacious pharmacological approaches. In this picture, ion channels represent an unexpected, but very promising, player. The expression and activity of different channel types mark and regulate specific stages of cancer progression. Their contribution to the neoplastic phenotype ranges from control of cell proliferation and apoptosis, to regulation of invasiveness and metastatic spread. As is being increasingly recognized, some of these roles can be attributed to signaling mechanisms independent of ion flow. Evidence is particularly extensive for K(+) channels. Their expression is altered in many primary human cancers, especially in early stages, and they frequently exert pleiotropic effects on the neoplastic cell physiology. For instance, by regulating membrane potential they can control Ca(2+) fluxes and thus the cell cycle machinery. Their effects on mitosis can also depend on regulation of cell volume, usually in cooperation with chloride channels. However, ion channels are also implicated in late neoplastic stages, by stimulating angiogenesis, mediating the cell-matrix interaction and regulating cell motility. Not surprisingly, the mechanisms of these effects are manifold. For example, intracellular signaling cascades can be triggered when ion channels form protein complexes with other membrane proteins such as integrins or growth factor receptors. Altered channel expression can be exploited for diagnostic purposes or for addressing traceable or cytotoxic compounds to specific neoplastic tissue. What is more, recent evidence indicates that blocking channel activity impairs the growth of some tumors, both in vitro and in vivo. This opens a new field for medicinal chemistry studies, which can avail of the many available tools, such as blocking antibodies, antisense oligonucleotides, small interfering RNAs, peptide toxins and a large variety of small organic compounds. The major drawback of this approach is that some ion channel blockers produce serious side effects, such as cardiac arrhythmias. Therefore, drug developing efforts aimed at producing less harmful compounds are needed and we discuss possible approaches toward this goal. Finally, we propose that a novel therapeutic tactic could be developed by unlocking ion channels from multiprotein membrane signaling complexes.

hERG1 channels are overexpressed in glioblastoma multiforme and modulate VEGF secretion in glioblastoma cell lines

Recent studies have led to considerable advancement in our understanding of the molecular mechanisms that underlie the relentless cell growth and invasiveness of human gliomas. Partial understanding of these mechanisms has (1) improved the classification for gliomas, by identifying prognostic subgroups, and (2) pointed to novel potential therapeutic targets. Some classes of ion channels have turned out to be involved in the pathogenesis and malignancy of gliomas. We studied the expression and properties of K⁺ channels in primary cultures obtained from surgical specimens: human ether a gò-gò related (hERG)1 voltage-dependent K⁺ channels, which have been found to be overexpressed in various human cancers, and human ether a gò-gò-like 2 channels, that share many of hERG1's biophysical features. The expression pattern of these two channels was compared to that of the classical inward rectifying K⁺ channels, IRK, that are widely expressed in astrocytic cells and classically considered a marker of astrocytic differentiation. In our study, hERG1 was found to be specifically overexpressed in high-grade astrocytomas, that is, glioblastoma multiforme (GBM). In addition, we present evidence that, in GBM cell lines, hERG1 channel activity actively contributes to malignancy by promoting vascular endothelial growth factor secretion, thus stimulating the neoangiogenesis typical of high-grade gliomas. Our data provide important confirmation for studies proposing the hERG1 channel as a molecular marker of tumour progression and a possible target for novel anticancer therapies.

Interneurons transiently express the ERG K+ channels during development of mouse spinal networks in vitro

During spinal cord maturation neuronal excitability gradually differentiates to meet different functional demands. Spontaneous activity, appearing early during spinal development, is regulated by the expression pattern of ion channels in individual neurons. While emerging excitability of embryonic motoneurons has been widely investigated, little is known about that of spinal interneurons. Voltage-dependent K+ channels are a heterogeneous class of ion channels that accomplish several functions. Recently voltage-dependent K+ channels encoded by erg subfamily genes (ERG channels) were shown to modulate excitability in immature neurons of mouse and quail. We investigated the expression of ERG channels in immature spinal interneurons, using organotypic embryonic cultures of mouse spinal cord after 1 and 2 weeks of development in vitro. We report here that all the genes of the erg family known so far (erg1a, erg1b, erg2, erg3) are expressed in embryonic spinal cultures. We demonstrate for the first time that three ERG proteins (ERG1A, ERG2 and ERG3) are co-expressed in the same neuronal population, and display a spatio-temporal distribution in the spinal slices. ERG immuno-positive cells, representing mainly GABAergic interneurons, were present in large numbers at early stages of development, while declining later, with a ventral to dorsal gradient. Patch clamp recordings confirmed these data, showing that ventral interneurons expressed functional ERG currents only transiently. Similar expression of the erg genes was observed at comparable ages in vivo. The role of ERG currents in regulating neuronal excitability during the earliest phases of spinal circuitry development will be examined in future studies.

Physical and functional interaction between integrins and hERG potassium channels

Integrins are adhesion receptors capable of transmitting intracellular signals that regulate many different cellular functions. Among integrin-mediated signals, the activation of ion channels can be included. We demonstrated that a long-lasting activation of hERG (human ether-a-go-go-related gene) potassium channels occurs in both human neuroblastoma and leukaemia cells after the activation of the β1 integrin subunit. This activation is apparently a determining factor inducing neurite extension and osteoclastic differentiation in both the cell types. More recently, we provided evidences that β1 integrins and hERG channels co-precipitate in both the cell types. Preliminary results suggest that a macromolecular signalling complex indeed occurs between integrins and the hERG1 protein and that hERG channel activity can modulate integrin downstream signalling.

Megaesophagus in an asthmatic patient and beta2 stimulant treatment by inhalation

Megaesophagus is a severe esophageal malformation. We report a case of megaesophagus in an asthmatic patient affected by congenital non-haemolytic anaemia and undergoing beta2 stimulant treatment by inhalation. Our case could be due to chronic beta2 receptor stimulation with imbalance of alpha and beta receptor, without any implication of favism.

Phosphatase inhibitors increase the open probability of ENaC in A6 cells

We studied the cellular phosphatase inhibitors okadaic acid (OKA), calyculin A, and microcystin on the epithelial sodium channel (ENaC) in A6 renal cells. OKA increased the amiloride-sensitive current after approximately 30 min with maximal stimulation at 1-2 h. Fluctuation analysis of cell-attached patches containing a large number of ENaC yielded power spectra with corner frequencies in untreated cells almost two times as large as in cells pretreated for 30 min with OKA, implying an increase in single channel open probability (P(o)) that doubled after OKA. Single channel analysis showed that, in cells pretreated with OKA, P(o) and mean open time approximately doubled. Two other phosphatase inhibitors, calyculin A and microcystin, had similar effects on P(o) and mean open time. An analog of OKA, okadaone, that does not inhibit phosphatases had no effect. Pretreatment with 10 nM OKA, which blocks protein phosphatase 2A (PP2A) but not PP1 in mammalian cells, had no effect even though both phosphatases are present in A6 cells. Several proteins were differentially phosphorylated after OKA, but ENaC subunit phosphorylation did not increase. We conclude that, in A6 cells, there is an OKA-sensitive phosphatase that suppresses ENaC activity by altering the phosphorylation of a regulatory molecule associated with the channel.

HERG potassium channels are constitutively expressed in primary human acute myeloid leukemias and regulate cell proliferation of normal and leukemic hemopoietic progenitors

An important target in the understanding of the pathogenesis of acute myeloid leukemias (AML) relies on deciphering the molecular features of normal and leukemic hemopoietic progenitors. In particular, the analysis of the mechanisms involved in the regulation of cell proliferation is decisive for the establishment of new targeted therapies. To gain further insight into this topic we report herein a novel approach by analyzing the role of HERG K(+) channels in the regulation of hemopoietic cell proliferation. These channels, encoded by the human ether-a-gò-gò-related gene (herg), belong to a family of K(+) channels, whose role in oncogenesis has been recently demonstrated. We report here that herg is switched off in normal peripheral blood mononuclear cells (PBMNC) as well as in circulating CD34(+) cells, however, it is rapidly turned on in the latter upon induction of the mitotic cycle. Moreover, hergappears to be constitutively activated in leukemic cell lines as well as in the majority of circulating blasts from primary AML. Evidence is also provided that HERG channel activity regulates cell proliferation in stimulated CD34(+) as well as in blast cells from AML patients. These results open new perspectives on the pathogenetic role of HERG K(+) channels in leukemias.

S-adenosyl-L-homocysteine hydrolase is necessary for aldosterone-induced activity of epithelial Na(+) channels

The A6 cell line was used to study the role of S-adenosyl-L-homocysteine hydrolase (SAHHase) in the aldosterone-induced activation of the epithelial Na(+) channel (ENaC). Because aldosterone increases methylation of several different molecules, and because this methylation is associated with increased Na(+) reabsorption, we tested the hypothesis that aldosterone increases the expression and activity of SAHHase protein. The rationale for this work is that general methylation may be promoted by activation of SAHHase, the only enzyme known to metabolize SAH, a potent end-product inhibitor of methylation. Although aldosterone increased SAHHase activity, steroid did not affect SAHHase expression. Antisense SAHHase oligonucleotide decreased SAHHase expression and activity. Moreover, this oligonucleotide, as well as a pharmacological inhibitor of SAHHase, decreased aldosterone-induced activity of ENaC via a decrease in ENaC open probability. The kinetics of ENaC in cells treated with antisense plus aldosterone were similar to those reported previously for the channel in the absence of steroid. This is the first report showing that active SAHHase, in part, increases ENaC open probability by reducing the transition rate from open states in response to aldosterone. Thus aldosterone-induced SAHHase activity plays a critical role in shifting ENaC from a gating mode with short open and closed times to one with longer open and closed times.

Cyclic-nucleotide-gated channels: pore topology in desensitizing E19A mutants

In cyclic-nucleotide-gated "CNG" channels, the pore-loop "P-loop" is formed by the amino acid residues R345-S371 (here called R1-S27). Residue E19 determines the channel's interaction with extracellular divalent cations and contributes to ion conduction. Neutralization of this residue with alanine introduces channel desensitization. We have used serial cysteine mutagenesis to study P-loop topology in the alpha subunit of the mammalian rod CNG channels containing the E19A substitution. The pore topology was tested in the closed channel state and, when cGMP was present, during and after desensitization. With E19A substitution, the T15C, T16C, I17C and T20C mutants desensitized more slowly than controls. Moreover, the typical rundown produced by the I17C substitution in the wild-type "w.t." background was considerably reduced. Overall, with the E19A substitution, the accessibility pattern tested by applying the thiol-specific reagents Cd2+ and MTSET from the cytoplasmic side of the plasma membrane was similar to that observed with the w.t. Moreover, P22C channels were not inhibited by Cd2+ and MTSET (which do not cross the lipid bilayer) applied from the inside, but were blocked by MTSEA (which permeates the plasma membrane) also applied from the inside. This suggests that the residues following E19 remain accessible from the external side after E19A substitution. Thus, although the residues T15 to T20 seemed to participate in the structural rearrangements producing desensitization, no major P-loop remodelling occurs in desensitizing channels.

HERG potassium channels are more frequently expressed in human endometrial cancer as compared to non-cancerous endometrium

HERG K(+)channels, besides contributing to regulate cardiac and neuronal excitability, are preferentially expressed in tumour cell lines of different histogenesis, where their role in the development and maintenance of the neoplastic phenotype is under study. We show here that both herg gene and HERG protein are expressed with high frequency in primary human endometrial cancers, as compared to normal and hyperplastic endometrium. RT-PCR and immunohistochemistry, using specific anti-HERG antibodies developed in our laboratory, were applied to tissue specimens obtained from 18 endometrial cancers and 11 non-cancerous endometrial tissues. herg RNA and HERG protein are expressed in 67% and 82%, respectively, of cancerous, while in only 18% of non-cancerous tissues. In particular, no expression was found in endometrial hyperplasia. Moreover, electrophysiological experiments confirmed the presence of functioning HERG channels on the plasma membrane of tumour cells. On the whole, these data are the first demonstration of the presence of HERG channels in primary human neoplasias, and could candidate HERG as a potential tool capable of marking cancerous versus hyperplastic endometrial growth.

The nicotinic receptor beta 2 subunit is mutant in nocturnal frontal lobe epilepsy

Clustered attacks of epileptic episodes originating from the frontal lobe during sleep are the main symptoms of autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE, MIM 600513). Despite the clinical homogeneity, three forms of ADNFLE have been associated with chromosomes 20 (ENFL1; ref. 1), 15 (ENFL2; ref. 2) and 1 (ENFL3; ref. 3). Mutations of the gene encoding the neuronal nicotinic acetylcholine receptor alpha 4 subunit (CHRNA4 ) have been found in ADNFLE-ENFL1 families, but these mutations account for only a small proportion of ADNFLE cases. The newly identified locus associated with ENFL3 harbours several candidate genes, including CHRNB2 (ref. 8), whose gene product, the beta 2 nicotinic acetylcholine receptor (nAChR) subunit, co-assembles with the alpha 4 nAChR subunit to form the active receptor.

Cyclic nucleotide-gated channels: intra- and extracellular accessibility to Cd2+ of substituted cysteine residues within the P-loop

In cyclic nucleotide-gated (CNG) channels from the bovine rod, the pore loop "P-loop", connecting the S5 and S6 transmembrane segments, is formed by the residues R345-S371 (here named R1-S27). It determines channel selectivity and contributes to gating. We have studied its topology, by testing the accessibility to Cd2+ of serially substituted cysteine residues. Channels were expressed in Xenopus oocytes. The accessibility of V4C, S6C, T16C, 117C, T20C, P22C and S27C from the cytoplasmic side of the plasma membrane was tested by applying 1-100 microM Cd2+ to the inner face of inside-out patches, at negative membrane potentials. Under these conditions, the effect of Cd2+ on wild-type channels was negligible. The accessibility of the same residues from the external side of the membrane was tested by measuring CNG current inhibition persisting after wash-out of Cd2+ applied to outside-out patches. T16C and I17C channels were strongly inhibited by Cd2+ from the inside, in the presence of cGMP. The Kd for T16C block was 16 microM. Thus the T16 and I17 residues participate directly in channel function and are accessible from the cytoplasmic side when the channels are open. In contrast, V4C, T20C and P22C residues were only inhibited when 100 microM Cd2+ was applied externally, suggesting that V4C, T20C and P22C face the outer side of the P-loop.

Methylation increases the open probability of the epithelial sodium channel in A6 epithelia

We used single channel methods on A6 renal cells to study the regulation by methylation reactions of epithelial sodium channels. 3-Deazaadenosine (3-DZA), a methyltransferase blocker, produced a 5-fold decrease in sodium transport and a 6-fold decrease in apical sodium channel activity by decreasing channel open probability (P(o)). 3-Deazaadenosine also blocked the increase in channel open probability associated with addition of aldosterone. Sodium channel activity in excised "inside-out" patches usually decreased within 1-2 min; in the presence of S-adenosyl-l-methionine (AdoMet), activity persisted for 5-8 min. Sodium channel mean time open (t(open)) before and after patch excision was higher in the presence of AdoMet than in untreated excised patches but less than t(open) in cell-attached patches. Sodium channel activity in excised patches exposed to both AdoMet and GTP usually remained stable for more than 10 min, and P(o) and the number of active channels per patch were close to values in cell-attached patches from untreated cells. These findings suggest that a methylation reaction contributes to the activity of epithelial sodium channels in A6 cells and is directed to some regulatory element closely connected with the channel, whose activity also depends on the presence of intracellular GTP.

The properties of cysteine mutants in the pore region of cyclic-nucleotide-gated channels

The properties of the pore of cyclic-nucleotide-gated channels are thought to depend mostly on the structure of the "P loop" which connects the S5 and S6 transmembrane segments. We applied scanning cysteine mutagenesis to the P loop of the alpha subunit of cGMP-gated channels from bovine rod, i.e. to the amino acid residues K346 to S371 (here named K2-S27). Mutant channels were expressed in Xenopus laevis oocytes and currents recorded from inside-out patches, in symmetrical sodium and in the absence of divalent cations. Cysteine mutations had minor effects on the affinity for cGMP and the selectivity to monovalent alkali cations. However, in mutants within the segment W9-T16, open probability was strongly reduced. It was less than 0.2 in saturating cGMP compared to 0.8 in wild-type channels. Moreover, W9C and L12C mutants were outward rectifiers, while T16C was an inward rectifier. These mutant channels showed a time dependence in the development of the steady-state current. Currents from I17C channels progressively decayed in inside-out patches. This rundown was prevented by 1 mM dithiothreitol on the cytoplasmic side of the plasma membrane, suggesting that I17 is an intracellular residue. On the other hand, mutants within the segment T20-S27 had normal open probabilities, around 0.8 in saturating cGMP, but altered single-channel conductance.

Low expression of the ClC-2 chloride channel during postnatal development: a mechanism for the paradoxical depolarizing action of GABA and glycine in the hippocampus

In early postnatal development, during the period of synapse formation, gamma-aminobutyric acid (GABA) and glycine, the main inhibitory transmitters in the adult brain, paradoxically excite and depolarize neuronal membranes by an outward flux of chloride. The mechanisms of chloride homeostasis are not fully understood. It is known that in adult neurons intracellular chloride accumulation is prevented by a particular type of chloride channel, the ClC-2. This channel strongly rectifies in the inward direction at potentials negative to ECl thus ensuring chloride efflux. We have tested the hypothesis that in the developing hippocampus, a differential expression or regulation of ClC-2 channels may contribute to the depolarizing action of GABA and glycine. We have cloned a truncated form of ClC-2 (ClC-2nh) from the neonatal hippocampus which lacks the 157 bp corresponding to exon 2. In situ hybridization experiments show that ClC-2nh is the predominant form of ClC-2 mRNA in the neonatal brain. ClC-2nh mRNA is unable to encode a full-length protein due to a frameshift, consequently it does not induce any currents upon injection into Xenopus oocytes. Low expression of the full-length ClC-2 channel, could alter chloride homeostasis, lead to accumulation of [Cl-]i and thereby contribute to the depolarizing action of GABA and glycine during early development.

Lithium blocks cell cycle transitions in the first cell cycles of sea urchin embryos, an effect rescued by myo-inositol

Lithium is a classical inhibitor of the phosphoinositide pathway and is teratogenic. We report the effects of lithium on the first cell cycles of sea urchin (Lytechinus pictus) embryos. Embryos cultured in 400 mM lithium chloride sea water showed marked delay to the cell cycle and a tendency to arrest prior to nuclear envelope breakdown, at metaphase and at cytokinesis. After removal of lithium, the block was reversed and embryos developed to form normal late blastulae. The lithium-induced block was also reversed by myo- but not epi-inositol, indicating that lithium was acting via the phosphoinositide pathway. Lithium microinjection before fertilization caused arrest prior to nuclear envelope breakdown at much lower concentrations (3-5 mM). Co-injection of myo-inositol prevented the block. Microinjection of 1–2 mM lithium led to block at the cleavage stage. This was also reversed by coinjection of myo-inositol. Embryos blocked by lithium microinjection proceeded rapidly into mitosis after photolysis of caged inositol 1,4,5-trisphosphate. These data demonstrate that a patent phosphoinositide signalling pathway is essential for the proper timing of cell cycle transitions and offer a possible explanation for lithium's teratogenic effects.

A novel inward-rectifying K+ current with a cell-cycle dependence governs the resting potential of mammalian neuroblastoma cells

1. Human and murine neuroblastoma cell lines were used to investigate, by the whole-cell patch-clamp technique, the properties of a novel inward-rectifying K+ current (IIR) in the adjustment of cell resting potential (Vrest), which was in the range -40 to -20 mV. 2. When elicited from a holding potential of 0 mV, IIR was completely inactivated with time constants ranging from 13 ms at -140 mV to 4.5 s at -50 mV. The steady-state inactivation curve (h(V)) was found to be independent of [Na+]o and [K+]o (2-80 mM) and could be fitted to a Boltzmann curve with a steep slope factor of 5-6, and a V1/2 around Vrest. Divalent ion-free extracellular solutions shifted h(V) to the left by about 28 mV. 3. Peak chord conductance, whose maximal value was approximately proportional to the square root of [K+]o, could be fitted to a Boltzmann curve independently of [K+]o, with a V1/2 value around -48 mV and a slope factor of 18. Extracellular Cs+ and Ba2+ blocked the IIR in a concentration- and voltage-dependent manner, but Ba2+ was less effective than it is on classical inward-rectifier channels. 4. Under control culture conditions the values of Vrest and V1/2 of h(V) varied widely among cells. The knowledge of V1/2 proved crucial or the theoretical prediction of Vrest. After cell synchronization in the G0-G1 phase of the cell cycle, or at the G1-S boundaries, the cells reduced their variability of h(V). The same occurred after cell synchronization in G1 by treatment with retinoic acid. 5. The experimental data could be fitted to a classical model of an inward rectifier, after removing the dependence of conductance activation on (V-EK), and incorporating an inactivation with an intrinsic voltage dependence. Moreover, the model predicts, for this novel inward rectifier and in contrast with the classical inward rectifier, the incapacity of maintaining, in physiological media, a Vrest more negative than -35 to -40 mV, which is an important feature of cancer cells.

Neuroblast long-term cell cultures from human fetal olfactory epithelium respond to odors

Primary cell cultures from human fetal olfactory neuroepithelium have been isolated, cloned, and propagated in continuous in vitro culture for approximately 1 year. The two clones we report here synthesize both neuronal proteins and olfactory-specific markers as well as the putative olfactory neurotransmitter, carnosine. In addition, patchclamp experiments reveal that these cells are electrically excitable. Following exposure to a panel of aromatic chemicals one of the cell cultures shows a specific increase in intracellular cAMP, indicating that some degree of functional maturity is expressed in vitro. The results suggest that these cells originate from the "stem cell" compartment that gives rise to mature olfactory receptor neurons. These long-term cell cultures represent models that will be useful in studying the mechanism(s) of olfaction and the regulation of olfactory neurogenesis and differentiation.

Leiomyosarcoma of the Scrotum

Scrotal leiomyosarcoma is a rare tumour which occurs in the muscular structures of the scrotum. Based on a recently observed case and on literature, the Authors discuss diagnostic and therapeutic problems of this tumour. The few cases observed do not allow definitive conclusions.

Integrin-mediated neurite outgrowth in neuroblastoma cells depends on the activation of potassium channels

Electrical signals elicited by integrin interaction with ECM components and their role in neurite outgrowth were studied in two clones (N1 and N7) isolated from 41A3 murine neuroblastoma cell line. Although the two clones similarly adhered to fibronectin (FN) and vitronectin (VN), this adhesion induced neurite outgrowth in N1 but not in N7 cells. Patch clamp recordings in whole cell configuration showed that, upon adhesion to FN or VN but not to platelet factor 4 (PF4), N1 cells undergo a marked (approximately equal to 20 mV) hyperpolarization of the resting potential (Vrest) that occurred within the first 20 min after cell contact with ECM, and persisted for approximately 1 h before reverting to the time zero values. This hyperpolarization was totally absent in N7 cells. A detailed analysis of the molecular mechanisms involved in N1 and N7 cell adhesion to ECM substrata was performed by using antibodies raised against the FN receptor and synthetic peptides variously competing with the FN or VN binding to integrin receptor (GRGDSP and GRGESP). Antibodies, as well as GRGDSP, abolished adhesion of N1 and N7 clones to FN and VN, revealing a similar implication of integrins in the adhesion of these clones to the ECM proteins. However, these anti-adhesive treatments, while ineffective on Vrest of N7 cells, abolished in N1 cells the FN- or VN-induced hyperpolarization and neurite outgrowth, that appeared therefore strictly associated and integrin-mediated phenomena. The nature of this association was deepened through a comparative analysis of the integrin profiles and the ion channels of N1 and N7 cells. The integrin immunoprecipitation profile resulted very similarly in the two clones, with only minor differences concerning the alpha V containing complexes. Both clones possessed Ca2+ and K+ delayed rectifier (KDR) channels, while only N1 cells were endowed with inward rectifier K+ (KIR) channels. The latter governed the Vrest, and, unlike KDR channels, were blocked by Ba2+ and Cs+. By moving patched cells in contact with FN-coated beads, it was shown that KIR channel activation was responsible for the FN-mediated hyperpolarization of Vrest. Treatment with Pertuxis toxin (PTX) abolished this hyperpolarization and neurite outgrowth, indicating that a G protein is interposed between integrins and KIR channels and that the activation of these channels is required for neuritogenesis. In fact, the block of KIR channels by Cs+ abolished both hyperpolarization and neurite outgrowth, provided that the cation was supplied during the first two hours after N1 cell contact with FN.(ABSTRACT TRUNCATED AT 400 WORDS)

Polar/apolar compounds induce leukemia cell differentiation by modulating cell-surface potential

The mechanism of action of polar/apolar inducers of cell differentiation, such as dimethyl sulfoxide and hexamethylene-bisacetamide, is still obscure. In this paper evidence is provided that their effects on murine erythroleukemia cells are modulated by various extracellular cations as a precise function of the cation effects on membrane surface potential. The interfacial effects of the inducers were directly measured on the charged electrode, showing that both dimethyl sulfoxide and hexamethylene-bisacetamide, at the effective concentrations for cell differentiation and within the physiological range of charge density, adsorb at the charged surface and produce a potential shift. A linear correlation was found between this shift and the inducer effects on cell differentiation. Besides offering a different interpretation of the mechanism of action of the inducers, these findings indicate that surface potential has a signaling function. They may also be relevant to cancer treatments based on tumor-cell commitment to terminal differentiation.

Intra and extracellular surface charges near Ca2+ channels in neurons and neuroblastoma cells

The properties of low (LVA) and high (HVA) voltage-activated calcium currents were investigated in rat sensory neurons and a murine neuroblastoma cell line exposed to various concentrations of intra- or extracellular monovalent ([c+]i/o) and trivalent ([c3+]i/o) cations. In neurons, when [c+]i was changed from 150 to 20 mM, positive shifts of 18-28 mV were observed in activation curves of both LVA and HVA currents, as well as in LVA inactivation curves. Extracellularly, in divalent-free solutions, [c+]o of 20-50 mM produced medium (12-22 mV) negative shifts of the LVA channel properties. These data were used to estimate, by a "screening" model, a negative surface charge density around neuron's calcium channels of 1/1,000 and 1/1,325 eA-2 at the outside or inside face, respectively. In the presence of physiological concentrations of divalent cations, [c+]o of 20-60 mM caused smaller (4-11 mV) negative shifts of the activation and inactivation curves, which can be explained by assuming a partial neutralization of negative charges by divalent cations. By applying the above procedure to LVA channels of neuroblastoma cells, the ratio of extra- to intracellular surface charge density turned out to be more than tenfold higher than in neurons. Effects produced by [c3+]i/o were not in agreement with expectations based on screening or binding models.

Response to fibronectin-integrin interaction in leukaemia cells: delayed enhancing of a K+ current

In murine erythroleukaemia cells, the response of ion channels was followed before and after contact with fibronectin-coated latex microspheres. Patch-clamp experiments in 'whole-cell' and in 'cell-attached' configurations showed that cell adhesion to fibronectin promoted plasma membrane hyperpolarization mediated by activation of potassium channels that were indistinguishable from calcium-dependent potassium channels K(Ca) in these cells. K+ current increase began in 5-6 min and was completed about 10 min after the first contact. The timecourse of this process recorded from 'whole-cell' was very similar to that followed in intact cells by observing the increase of single channel currents. The open probability of single channels in the patch increased after contact, revealing that this activation is propagated at distance from the adhesion site. The slow onset of the effect suggests the presence of a complex regulatory pathway between fibronectin-integrin binding and activation of potassium channels. Decreasing cytoplasmic free Ca2+ concentration to pCa 9 diminished, but did not inhibit, the response. The current induced by fibronectin was not blocked by apamin, alpha-charybdotoxin or glibenclamide, but was abolished by high concentrations of tetraethylammonium (TEA). These data suggest for the first time the existence of a specific regulative connection between integrin receptors and ionic channels.

Effects of inhibitors of ion-motive ATPases on the plasma membrane potential of murine erythroleukemia cells

The membrane electric effects of N,N'-dicyclohexyl-carbodiimide (DCCD) and vanadate were studied in murine erythroleukemia cells (MELC), comparing the patch-clamp technique and the accumulation ratio (ARexp) of [3H]-tetraphenylphosphonium (TPP+). Electrophysiological measurements showed that both these inhibitors produce, at micromolar concentrations, a 20-30 mV hyperpolarization of resting potential (delta psi p) of MELC, which is abolished when the electrochemical equilibrium potential of K+ (EK) is brought close to zero. DCCD and vanadate turned out to have distinct targets on the plasma membrane of MELC (an H+ pump and the Na+,K(+)-ATPase, respectively). Measurements of ARexp showed that: (i) patch-clamp measurements of delta psi p were equivalent to those based on ARexp of antimycin-pretreated cells (ARANT); (ii) DCCD produced a strong increase in ARANT, that was antagonized by carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone (FCCP) and diethylstilbestrol (DES); (iii) vanadate determined a marked increase in ARANT that was insensitive to FCCP, but antagonized by ouabain; (iv) incubation in high K+ medium (HK) brought ARANT to 1.0 in the controls, but did not lower this ratio below 3.0 in the presence of DCCD or vanadate; (v) the total amount of TPP+ taken up by the cells was in any case water extractable by a freezing and thawing procedure. On the whole, our data indicate that DCCD and vanadate hyperpolarize the MELC by increasing the K+ conductance and, at the same time, enhance the TPP+ binding, probably by changing the electrostatic potential profile of the plasma membrane. These effects seem to involve functional modifications of the target pumps, apparently related to the ion-occluding state of these enzymes.

Fibronectin-integrin binding promotes hyperpolarization of murine erythroleukemia cells

The resting electrical potential (delta psi p) of murine erythroleukemia cells (MELC) was measured by the patch-clamp technique at different times after seeding onto culture surfaces enriched with bovine serum albumin (BSA) or Fibronectin (FN). While BSA did not produce significant changes of potential and cell shape, FN promoted a 15-20 mV hyperpolarization that preceded a marked cell spreading. This hyperpolarization was abolished by either treating cells with anti FN-receptor antibodies, or adding the RGDS tetrapeptide, suggesting that electric signals are elicited by the specific interaction of the FN cell binding domain with integrin receptors.

Cross-talk between receptors coupled to calcium currents in adult but not neonatal rat sensory neurons

In adult rat sensory neurons Ca2+ currents were studied with the whole-cell patch-clamp technique. Two categories of neuromodulators, known to activate different 2nd messenger systems: 1) angiotensin II (AII), bovine serum albumin (BSA), Acetylcholine (ACh) and 2) GABA, stimulated the low-voltage activated (LVA) and inhibited the high voltage activated (HVA) currents, respectively. The simultaneous application of the two types of drugs failed to inhibit the HVA current via a putative cross-talk between the two 2nd messengers.