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Biomedical subjects

M A Rizzo

Publications and source records attributed to M A Rizzo.

18 recordsLinked to original sources
PubMed2004

Prevalence and treatment of spasticity reported by multiple sclerosis patients.

The objective of this study was to characterize the population of multiple sclerosis (MS) patients suffering from spasticity and to evaluate treatment patterns, including intrathecal baclofen (ITB) delivery, related to patient quality of life (QOL). We conducted a cross-sectional, two-level study using data from the Patient Registry of the North American Research Committee on MS (NARCOMS). In addition, we surveyed a subgroup of 198 preselected patients who are using ITB (ITBG) and a random sample of 315 oral drug users (ORALG). Among the registrants, 16% reported no spasticity, 31% minimal, 19% mild, 17% moderate (frequently affects activities), 13% severe (daily forced to modify activities) and 4% total (prevents daily activities). Patients experiencing greater severity included by proportion males, and those older and with longer duration of MS. QOL scores decreased inversely with severity. In the focused survey, ITBG reported lower levels of spasticity than ORALG, less stiffness in the legs, less pain and fewer spasms at any time. They scored significantly lower in the SF-36 physical component, yet reported less fatigue on the MFIS scale. Prevalence data reveal that one third of MS patients modify or eliminate daily activities as a result of spasticity. Treatment of spasticity can significantly impact QOL parameters by reducing spasms, pain and fatigue.

Administration, Oral↗
PubMed2003

Glatiramer acetate (Copaxone): comparison of continuous versus delayed therapy in a six-year organized multiple sclerosis trial.

The aim of this study was to assess the long-term safety and efficacy of glatiramer acetate (GA) for patients with multiple sclerosis (MS) who received active treatment versus those on placebo for approximately 30 months (24-35 months) before receiving GA during a six-year organized, prospective open label study. Entry required two relapses in the previous two years and an Expanded Disability Status Scale (EDSS) score of 0-5. Patients (251) were equally randomized to daily subcutaneous GA, 20 mg, or to placebo. After approximately 30 months, 208 patients continued in an open label study: 101 continued on GA and 107 switched from placebo to active drug. Groups were well matched at randomization and entry to the open label study. Patients always on GA showed a steady decline in relapses: a mean of 1.5 per year at entry, a mean of 0.42 over the entire six years (95% CI = 0.34-0.51), a 72% reduction (P = 0.0001). They averaged a relapse every four + years (yearly rate 0.23 in year six) and 26/101 remain relapse free. Patients did less well if on placebo for 30 months, but relapses then declined, and by year six the rates were similar. Of patients always on GA, 69% showed neurological improvement of > or = 1 EDSS steps or remained stable compared with 57% if GA treatment was delayed. Of relapse-free patients always on GA over six years, only three of 26 (11%) were worse by > or = 1 EDSS steps, whereas nine of 21 (43%) in the placebo/active group were worse (P < 0.03). Disability, measured every six months, showed that the group of patients always on GA was relatively stable over the six years, while the group who received placebo for the first two-and-a-half years did significantly less well. Daily injections of GA were well tolerated. This longest ever organized MS treatment trial shows that delaying therapy with GA increases the risk of neurologic disability, reinforcing the rationale for using GA as a first-line treatment early in the course of relapsing-remitting MS.

Disability Evaluation↗
PubMed2000

The activation of phospholipase D by endothelin-1, angiotensin II, and platelet-derived growth factor in vascular smooth muscle A10 cells is mediated by small G proteins of the ADP-ribosylation factor family.

We show here that A10 cells express the phospholipase D (PLD) isoforms PLD1b and PLD2. The activation of PLD in these cells by angiotensin II (AngII), endothelin-1 (ET-1), and platelet-derived growth factor (PDGF) was found to be sensitive to inhibitors of the activation of ADP-ribosylation factor (ARF) but not to blockers of Rho protein function. PDGF, AngII, and ET-1 induced the binding of ARF proteins to cell membranes in a permeabilized cell assay. Cells permeabilized and depleted of ARF were no longer sensitive to stimulation with AngII, ET-1, or PDGF, but the addition of recombinant myristoylated human ARF1 restored agonist-dependent PLD activity. Expression of dominant negative ARF mutants blocked receptor-dependent activation of PLD. PLD activity was also potently stimulated by treatment with phorbol esters, but this activity was only partially inhibited by brefeldin A or by the overexpression of ARF dominant negative mutants. Transient expression of catalytically inactive mutants of PLD2, but not PLD1, inhibited significantly PDGF- and AngII-dependent PLD activity. We conclude: 1) the activation of PLD by cell surface receptors occurs primarily by an ARF-dependent mechanism in A10 cells, whereas the activation of PLD by protein kinase C-dependent pathways is only partially dependent on the regulation of ARF proteins; and 2) cell surface receptors, such as AngII and PDGF, signal primarily via PLD2 in A10 cells.

ADP Ribose Transferases↗
PubMed1998

Characterization of cationic lipid-protamine-DNA (LPD) complexes for intravenous gene delivery.

A previous study has shown an efficient, systemic transgene expression in mice via intravenous administration of a LPD formulation composed of DOTAP liposomes, protamine sulfate and plasmid DNA. In this study, factors affecting the in vivo performance of this formulation were further evaluated. A protocol in which liposomes were mixed with protamine before the addition of plasmid DNA was shown to produce small condensed particles with a diameter of about 135 nm. These particles were stable over time and gave a high level of gene expression in all tissues examined including lung, heart, spleen, liver and kidney with the highest level of expression in the lung. Inclusion of dioleoylphosphatidylethanolamine (DOPE) as a helper lipid significantly decreased the in vivo activity of LPD. In contrast, inclusion of cholesterol as a helper lipid increased the in vivo transfection efficiency of LPD and more importantly, decrease the amount of cationic lipid required for the maximal level of gene expression. Studies on the interaction between mouse serum and LPD showed that LPD became negatively charged after exposure to serum, and LPDs containing different helper lipids varied in the amount of associated serum proteins. LPD containing DOPE was more enriched in a protein corresponding to albumin in molecular weight. These results suggest that the mechanism of LPD-mediated intravenous gene delivery might be different from that of in vitro lipofection and that serum protein association might be a major factor limiting the in vivo transfection by LPD.

Animals↗
PubMed1998

Morphologically identified cutaneous afferent DRG neurons express three different potassium currents in varying proportions.

Outward K+ currents were recorded using a whole cell patch-clamp configuration, from acutely dissociated adult rat cutaneous afferent dorsal root ganglion (DRG) neurons (L4 and L5) identified by retrograde labeling with Fluoro-gold. Recordings were obtained 16-24 h after dissociation from cells between 39 and 49 mm in diameter with minimal processes. These cells represent medium-sized DRG neurons relative to the entire population, but are large cutaneous afferent neurons giving rise to myelinated axons. Voltage-activated K+ currents were recorded routinely during 300-ms depolarizing test pulses increasing in 10-mV steps from -40 to +50 mV; the currents were preceded by a 500-ms conditioning prepulse of either -120 or -40 mV. Coexpression of at least three components of K+ current was revealed. Separation of these components was achieved on the basis of sensitivities to the K+ channel blockers, 4-aminopyridine (4-AP) and dendrotoxin (DTx), and by the current responses to variation in conditioning voltage. Changing extracellular K+ concentration from 3 to 40 mM resulted in a shift to the right of the I-V curve commensurate with K+ being the principal charge carrier. Presentation of 100 mM 4-AP revealed a rapidly activating K+ current sensitive to low concentrations of 4-AP. High concentrations of 4-AP (6 mM) extinguished all inactivating current, leaving almost pure sustained current (IK). On the basis of the relative distribution of K+ currents neurons could be separated into three distinct categories: fast inactivating current (IA), slow inactivating current (ID), and sustained current (IK); only IA and IK; and slow inactivating current and IK. However, IK was always the dominant outward current component. These results indicate that considerable variation in K+ currents is present not only in the entire population of DRG neurons, as previously reported, but even within a restricted size and functional group (large cutaneous afferent neurons).

4-Aminopyridine↗
PubMed1998

The role of G proteins in insulin signalling.

Insulin modulates many intracellular processes including cellular metabolism, cell proliferation and cell differentiation. Some of these processes involve significant changes in the traffic of intracellular vesicles or in the structural organization of the cell. These phenomena have been linked to the activity of regulatory GTP-binding proteins. Most, if not all functions, of the insulin receptor are associated with its tyrosine kinase activity. Thus, over the past few years, a significant effort has been dedicated to elucidate the cross-talk between the tyrosine kinase activity of the receptor and the regulation of G protein-mediated pathways. Recent progress indicates that G proteins may mediate the control of several of insulin's intracellular functions. These include the regulation of the MAP kinase pathway, the activation of phospholipase D and the regulation of glucose uptake. This article discusses some recent advances in this area.

Animals↗
PubMed1997

Successful treatment of painful traumatic mononeuropathy with carbamazepine: insights into a possible molecular pain mechanism.

The delayed onset of painful paresthesias following trauma to a peripheral nerve is a well recognized but poorly understood phenomenon. This report describes an illustrative case of painful paresthesias in the territory of the ilioinguinal nerve, 3 to 6 weeks after an otherwise routine herniorraphy, which subsequently responded dramatically to carbamazepine. The case is considered in light of recent studies which have determined molecular changes which occur in dorsal root ganglion (DRG) neurons following axotomy and neuroma formation. Voltage-dependent sodium (Na+) channels in DRG neurons undergo a change following axotomy, in which there is significant up- and down-regulation of different subpopulations of Na channels over a time frame measured in days to weeks. Such changes may render the DRG neurons hyperexcitable, thus contributing to a neuropathic pain syndrome, yet susceptible to treatment with a sodium channel blocker such as carbamazepine.

Analgesics, Non-Narcotic↗
PubMed1997

TTX-sensitive and -resistant Na+ currents, and mRNA for the TTX-resistant rH1 channel, are expressed in B104 neuroblastoma cells.

To examine the molecular basis for membrane excitability in a neuroblastoma cell line, we used whole cell patch-clamp methods and reverse transcription-polymerase chain reaction (RT-PCR) to study Na+ currents and channels in B104 cells. We distinguished Tetrodotoxin (TTX)-sensitive and -resistant Na+ currents and detected the mRNA for the cardiac rH1 channel in B104 cells. Na+ currents could be recorded in 65% of cells. In the absence of TTX, mean peak Na+ current density was 126 +/- 19 pA/pF, corresponding to a channel density of 2.7 +/- 0.4/micron 2 (mean +/- SE). Time-to-peak (t-peak), activation (tau m), and inactivation time constants (tau h) for Na+ currents in B104 cells were 1.0 +/- 0.04, 0.4 +/- 0.06, and 0.9 +/- 0.04 ms at -10 mV. The peak conductance-voltage relationship had a V 1/2 of -39.8 +/- 1.5 mV. V 1/2 for steady-state inactivation was -81.6 +/- 1.5 mV. TTX-sensitive and -resistant components of the Na current had half-maximal inhibitions (IC50), respectively, of 1.2 nM and, minimally, 575.5 nM. The TTX-sensitive and -resistant Na+ currents were kinetically distinct; time-to-peak, tau m, and tau h for TTX-sensitive currents were shorter than for TTX-resistant currents. Steady-state voltage dependence of the two currents was indistinguishable. The presence of TTX-sensitive and -resistant Na+ currents, which are pharmacologically and kinetically distinct, led us to search for mRNAs known to be associated with TTX-resistant channels, in addition to the alpha subunit mRNAs, which have previously been shown to be expressed in these cells. Using RT-PCR and restriction enzyme mapping, we were unable to detect alpha SNS, but detected mRNA for rH1, which is known to encode a TTX-resistant channel, in B104 cells. B104 neuroblastoma cells thus express TTX-sensitive and -resistant Na+ currents. These appear to be encoded by neuronal-type and cardiac Na+ channel mRNAs including the RH1 transcript. This cell line may be useful for studies on the rH1 channel, which is known to be mutated in the long-QT syndrome.

Brain Neoplasms↗
PubMed1997

Differential effects of NGF and BDNF on axotomy-induced changes in GABA(A)-receptor-mediated conductance and sodium currents in cutaneous afferent neurons.

The effects of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) on injury-induced changes in the electrophysiological properties of adult rat cutaneous afferent dorsal root ganglion (DRG) neurons were examined. Whole cell patch-clamp techniques were used to study gamma-aminobutyric acid-A (GABA(A))-receptor-mediated conductance, voltage-dependent sodium currents, and action potential waveform in cutaneous afferent neurons (35-60 microm diam) cultured from control and axotomized animals. Cutaneous afferent neurons were identified by retrograde labeling with hydroxy-stilbamidine (Fluoro-gold, a fluorescent retrograde axonal tracer); the sciatic nerve was transected 1 wk after Fluoro-gold injection and L4/L5 DRG neurons were cultured 2-3 wk after axotomy. NGF, BDNF, or Ringer (vehicle) solution was delivered in vivo directly to the transected sciatic nerve stump in axotomized rats via an osmotic pump. Recordings were obtained from neurons 5-24 h after culture. Axotomized neurons from rats treated with vehicle solution displayed a twofold increase in GABA-induced conductance and a prominent reduction in the proportion of neurons expressing action potentials that had inflections on the falling phase. The expression of kinetically slow tetrodotoxin (TTX)-resistant sodium current was markedly reduced and an increased expression of kinetically fast TTX-sensitive current was observed in neurons from vehicle-treated, axotomized rats. Treatment with NGF (0.25 microg/microl at 12 microl/day for 14 days) in axotomized animals resulted in an increase in the proportion of neurons expressing TTX-resistant, slow sodium currents and inflected action potentials, but had no effect on GABA-induced conductance. Treatment with BDNF (0.5 microg/microl at 12 microl/day for 14 days) attenuated the axotomy-induced increase in GABA(A)-receptor-mediated conductance while minimally affecting action potential waveform. The observed neurotrophin effects occurred independently of cell size changes. These findings indicate a differential regulation of GABA(A) receptor and sodium channel properties in axotomized rat cutaneous afferent neurons by specific neurotrophic factors.

Animals↗
PubMed1996

Spinal sensory neurons express multiple sodium channel alpha-subunit mRNAs.

The expression of sodium channel alpha-, beta 1- and beta 2-subunit mRNAs was examined in adult rat DRG neurons in dissociated culture at 1 day in vitro and within sections of intact ganglia by in situ hybridization and reverse transcription polymerase chain reaction (RT-PCR). The results demonstrate that sodium channel alpha-subunit mRNAs are differentially expressed in small (< 25 microns diam), medium (25-45 microns diam.) and large (> 45 microns diam.) cultured DRG neurons at 1 day in vitro (div). Sodium channel mRNA I is expressed at higher levels in large neurons than small DRG neurons, while sodium channel mRNA II is variably expressed, with most cells lacking or exhibiting low levels of detectable signal of these mRNAs and limited numbers of neurons with moderate expression levels. DRG neurons generally exhibit negligible or low levels of hybridization signal for sodium channel mRNA III. Sodium channel mRNAs Na6 and NaG show similar patterns of expression, with most large and many medium DRG neurons exhibiting high levels of expression. The mRNA for the rat cognate of human sodium channel hNE-Na is detected in virtually every DRG neuron; most cells in all size classes exhibit moderate or high levels of hNE-Na expression. Sodium channel SNS mRNA is expressed in all size classes of DRG neurons, but shows greater expression in small and medium DRG neurons than in large neurons. The mRNA for the rat cognate of mouse sodium channel mNa 2.3 is not detected, or is detected at low levels, in most DRG neurons, regardless of size, although moderate expression is detected in some neurons. Sodium channel beta 1- and beta 2-subunit mRNAs exhibit similar expression patterns; they are detected in most DRG neurons, although the level of expression tends to be greater in large neurons than in small neurons. RT-PCR and in situ hybridization of intact adult DRG showed a similar pattern of expression of sodium channel mRNAs to that observed in DRG neurons in vitro. These results demonstrate that adult DRG neurons express multiple sodium channel mRNAs in vitro and in situ and suggest a molecular basis for the biophysical heterogeneity of sodium currents observed in these cells.

Animals↗
PubMed1996

Mechanisms of paresthesiae, dysesthesiae, and hyperesthesiae: role of Na+ channel heterogeneity.

Paresthesiae, dysesthesiae, and hyperesthesiae ('positive symptoms') result from ectopic nerve impulses secondary to inappropriate membrane excitability which develops in the setting of chronic sensory axonal injury. The molecular changes in the membranes of dorsal root ganglion neurons which underlie ectopic impulse generation as a result of chronic axonal injury are unknown. Preliminary evidence has suggested that voltage-dependent Na+ channels are one of the participants in the production of ectopic impulses, but the precise form of their participation remains to be determined. The present paper reviews normal sensory anatomy and Na+ channel physiology, as well as clinical syndromes heralded by positive sensations and what is so far known about the cellular and molecular mechanisms underlying them. Properties of two distinct populations of Na+ channels native to the DRG neurons which give rise to cutaneous afferents are described. The biophysical properties of each population of Na+ channels must be tuned with respect to the other in order to cooperate in the generation of action potential activity underlying normal sensory function. A novel hypothesis is put forth suggesting that chronic axonal injury leads to intraneuronal heterogeneity of the populations of Na+ channels in cutaneous afferents, as revealed by their characteristic properties. This may result in one population of Na+ channels activating the other, leading to membrane instability, and possibly to ectopic impulse generation.

Axons↗
PubMed1995

Selective loss of slow and enhancement of fast Na+ currents in cutaneous afferent dorsal root ganglion neurones following axotomy.

Voltage-dependent Na+ currents were recorded via patch-clamp from identified adult rat lumbar cutaneous dorsal root ganglion (DRG) neurones using whole-cell and bleb-patch-clamp configurations. Na+ currents in DRG neurones studied 18 days after sciatic nerve ligation were compared with those in control neurones. Control neurones tended to have a singular kinetically slow Na+ current or net Na+ current suggestive of two kinetic varieties of channel in a single neurone. Three changes occurred following axotomy: (1) the peak Na+ current increased significantly, (2) kinetically slow TTX-resistant Na+ current, which predominated in controls, was significantly attenuated or lacking altogether, and (3) a singular, TTX-sensitive kinetically fast form of Na+ current predominated. These findings suggest that as part of the response to axonal injury, DRG neurones increase Na+ channel biosynthesis and/or modify preexisting channels such that their kinetics are accelerated. The results are consistent with the idea that axotomized DRG neurones become hyperexcitable due to the emergence of a high density of kinetically fast, pharmacologically distinguishable, Na+ channels in the membrane.

Animals↗
PubMed1994

Delayed depolarization and slow sodium currents in cutaneous afferents.

1. Intraaxonal recordings were obtained in vitro from the sural nerve (SN), the muscle branch of the anterior tibial nerve (ATN), or the deafferented ATN (dATN) in 5- to 7-wk-old rats. Whole-nerve sucrose gap recordings were obtained from the SN and the ATN. This allowed study of cutaneous (SN), mixed motor and muscle afferent (ATN), and isolated muscle afferent (dATN) axons. 2. Application of the potassium channel blocking agent 4-aminopyridine (4-AP) to ATN or dATN resulted in a slight prolongation of the action potential. In contrast, a distinct delayed depolarization followed the axonal action potential in cutaneous afferents (SN) exposed to 4-AP. The delayed depolarization could be induced by a single whole-nerve stimulus or by injection of constant-current depolarizing pulses into individual axons. The delayed depolarization often gave rise to bursts of action potentials and was followed by a prominent afterhyperpolarization (AHP). 3. In paired-pulse experiments on single SN axons, the recovery time (half-amplitude of the action potential) was 3.06 +/- 1.82 (SE) ms (n = 12). After exposure to 4-AP the recovery time of the delayed depolarization was considerably longer (half-recovery time: 99.0 +/- 28.3 ms; n = 15) than that of the action potential (18.8 +/- 9.1 ms; n = 16). 4. Application of tetraethylammonium (TEA) to cutaneous or muscle afferents alone had little effect on single action potential waveform. However, TEA reduced the amplitude of the AHP elicited by a single stimulus in cutaneous afferent axons after exposure to 4-AP and resulted in repetitive spike discharge. 5. The delayed depolarization and spike burst activity induced by 4-AP in SN was present in Ca(2+)-free solutions containing 1 mM ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and was not blocked by Cd2+ (1.0 mM). 6. We obtained whole-cell patch-clamp recordings to study Na+ currents from either randomly selected dorsal root ganglion neurons or cutaneous afferent neurons identified by retrograde labeling with Fluoro-Gold. The majority of the randomly selected neurons had a singular kinetically fast Na+ current. In contrast, no identified cutaneous afferent neurons had a singular fast Na+ current. Rather, they had a combination of kinetically separable fast and slow currents or a singular relatively slow Na+ current.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Aminopyridine↗
PubMed1994

Slow sodium conductances of dorsal root ganglion neurons: intraneuronal homogeneity and interneuronal heterogeneity.

1. Voltage-dependent Na+ conductances were studied in small (18-25 microns diam) adult rat dorsal root ganglion (DRG) neurons with the use of the whole cell patch-clamp technique. Na+ currents were also recorded from larger (44-50 microns diam) neurons and compared with those of the small neurons. 2. The predominant Na+ conductance in the small neurons was selective over tetramethylammonium by at least 10-fold and was resistant to 1 microM external tetrodotoxin (TTX). Na+ conductances in many larger DRG neurons were kinetically faster and, in contrast, were blocked by 1 microM TTX. 3. The Na+ conductance in the small neurons was kinetically slow. Activation half-times were voltage dependent and ranged from 2 ms at -20 mV to 0.7 ms at +50 mV. Approximately 50% of the activation half-time was comprised of an initial delay. Inactivation half-times were voltage dependent and ranged from 11 ms at -20 mV to 2 ms at +50 mV. 4. Peak slow Na+ conductances were near maximal with conditioning potentials negative to -120 mV and were significantly reduced or eliminated with conditioning potentials positive to -40 mV. The slow Na+ conductance increased gradually with test potentials extending from -40 to +40 mV. In some cells the conductance could be saturated at +10 mV. Peak conductance/voltage relationships, although stable in a given neuron, revealed marked variability among neurons, spanning > 20- and 50-mV domains for steady-state activation and inactivation (current availability), respectively. 5. Kinetics remained stable within a given neuron over the course of an experiment. However, considerable kinetic variation was exhibited from neuron to neuron, such that the half-times of activation and of inactivation spanned an order of magnitude. In all small neurons studied there appeared to be a singular kinetic component of the current, based on sensitivity to the conditioning potential, voltage dependence of activation, and inactivation half-time. 6. Unique closing properties were exhibited by Na+ channels of the small neurons. Hyperpolarization following a depolarization-induced fully inactivated state resulted in tail currents that appeared to be the consequence of reactivation of the slow Na+ conductance. Tail currents recorded at various times during a fixed level of depolarization revealed that the underlying channels accumulated into a volatile inactivated state over the course of the preceding depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Hypermagnesemic pseudocoma.

We treated a case of iatrogenic hypermagnesemia that clinically mimicked a central brain-stem herniation syndrome. Hypermagnesemia (magnesium level, 9.85 mmol/L [24 mg/dL]) can cause parasympathetic blockade, inducing fixed and dilated pupils, in addition to neuromuscular blockade. Extreme hypermagnesemia can therefore mimic a midbrain syndrome and cause a pseudocomatose state.

Adult↗
PubMed1992

Transient K current in the somatic membrane of cultured central neurons of embryonic rat.

1. Somatic K currents of cultured hippocampal, striatal, and spinal cord neurons of embryonic rat were recorded under voltage clamp in membrane spheres ("blebs") excised by means of a tight-seal pipette. 2. The somatic K current in blebs was subject to rapid and near complete inactivation during 300-ms depolarizations, whereas whole-cell K currents included a substantial maintained component. Size and kinetic properties of bleb and whole-cell currents were stable throughout the recording period. 3. The steady-state inactivation of somatic A current was steeply voltage dependent and complete near voltage levels that activated current, whereas peak conductances did not saturate during depolarizations up to +90 mV. Activation started with a delay. Half-times of activation decreased with depolarization, but half-times of inactivation varied little with depolarization. Recovery from inactivation followed a sigmoidal time course with half-times of approximately 50 ms. 4. Half-times of activation and inactivation varied over more than an order of magnitude between individual neurons. Midpoint potentials of inactivation and peak conductance varied over approximately 40 mV. The parameter ranges of hippocampal, striatal, and spinal cord neurons overlapped. 5. Individual soma membranes revealed signs of K channel heterogeneity in their 4-aminopyridine block, current fluctuations, and current kinetics. On the other hand, currents elicited after conditioning pulses that established varied degrees of steady-state inactivation or of recovery from full inactivation had superimposable time courses. 6. The described characteristics of the somatic A channels are compared with those reported for the RCK4, Raw3, and mShal products expressed in Xenopus oocytes. Whereas the ranges of voltage dependencies and of most kinetic characteristics are compatible among native and cloned channels, these three cloned channels recover much more slowly from inactivation. In addition, inactivation in native channels, unlike that in RCK4 and Raw3 channels, was stable after excision in a subcellular fragment.

4-Aminopyridine↗
PubMedDate not supplied

Stimulation of tumor cell growth in vitro by a monoclonal antibody to a tumor specific protein (TSP-180) present on the cell surface of 3LL cells.

Proliferation capacity and MHC class I antigen expression of two Lewis lung carcinoma (3LL) metastatic variants (C87, BC215) grown under defined experimental conditions (serum-free defined medium or 10 per cent serum) have been studied following exposure to MoAb 135-13C which recognizes on these cells a tumor surface protein of 180,000 daltons (TSP-180). The results of this study indicate that the high metastatic clone (C87) binds higher amounts of MoAb to TSP-180 and Db antigens than does the low metastatic one (BC215), while both clones express very low amounts of Kb antigens. 3LL clones grown in 10 per cent serum or adapted in serum-free, defined medium show the same metastatic phenotype and MHC class I antigen expression, but when grown in defined medium exhibit increased capacity to bind MoAb 135-13C. However, the relative binding rate of 3LL clones grown in 10 per cent serum or in defined medium is unchanged: the high metastatic clone always showing higher capacity to bind MoAb to TSP-180. Furthermore, comparison of EGF binding sites on the cell surface of 3LL clones, grown in different culture conditions, demonstrates that the C87 clone binds higher amounts of labelled EGF and that this amount increases in serum-free defined medium, exactly as reported for TSP-180. In addition, competition experiments demonstrated that MoAb 135-13C does not compete for EGF binding sites on 3LL cell surface. Studies on cell proliferation following exposure to MoAb 135-13C, revealed that the low metastatic clone (BC215) is more actively stimulated than the high metastatic one. Moreover, similar data were obtained after exposure of 3LL clones to physiological amounts of different growth factors (i.e. EGF, MSA, insulin). Analysis of MHC class I antigen expression following exposure to MoAb 135-13C indicated that MoAb 135-13C induces on the cell surface of the C87 clone a transient low modulation of Db antigens. These results suggest that 3LL cells endowed with lower metastatic potential are more dependent on the microenvironmental conditions than the high metastasizing ones, and that MoAb 135-13C binding to 3LL cell surface stimulates proliferation as reported for several known growth factors.

Animals↗