SEARCH · PubMed Health

Results for “Intracellular quantification”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources

PubMed1998

Differential induction of functional B1-bradykinin receptors along the rat nephron in endotoxin induced inflammation.

BACKGROUND: Under physiological conditions, the effects of kinins in the kidney are mainly mediated by the bradykinin B2-receptor, whereas the kinin B1-receptor is strongly induced under inflammatory conditions in a variety of tissues. Knowledge of the distribution of the B1-receptor along the nephron is of importance since the B1-receptor might replace B2-receptors under these conditions. METHODS: Using a RT-PCR/Southern blot approach allowing relative quantification of mRNA levels, ten different microdissected rat nephron segments were analyzed for the presence of the B1- and B2-receptor before and after endotoxin treatment to induce experimental inflammation. The functionality of the expressed receptors was assessed by kinin-induced intracellular calcium ([Ca2+]i) mobilization in microdissected nephron segments. RESULTS: While under physiological conditions no B1-receptor mRNA could be detected, after 18 hours of treatment with bacterial lipopolysaccharide (LPS) the expression of B1-receptor mRNA was strongly induced in the efferent arteriole, the medullary and inner medullary thin limb, and in the distal tubule. Moderate expression was found in the glomerulus, proximal convoluted and straight tubules, and in the medullary thick ascending limb. Small but detectable expression was observed in the cortical collecting duct. The induction of B1-receptor mRNA expression resulted in functional receptor expression, since increases in [Ca2+]i were observed upon B1-agonist stimulation. LPS treatment also increased the expression of B2-receptor mRNA in all nephron segments except in the glomerulus, the inner medullary thin limb and the outer medullary collecting duct. However, no related changes in B2-agonist induced rises in [Ca2+]i were found. CONCLUSIONS: These studies show a functional induction of the B1-kinin receptor along the rat nephron, which should be taken in account to address the effects of kinins under inflammatory conditions in the kidney.

Animals↗

PubMed2000

A novel sensitive approach for frequency analysis of measles virus-specific memory T-lymphocytes in healthy adults with a childhood history of natural measles.

Measles virus (MV), a single-stranded negative-sense RNA virus, is an important pathogen causing almost 1 million deaths annually. Acute MV infection induces immunity against disease throughout life. The immunological factors which are responsible for protection against measles are still poorly understood. However, T-cell-mediated immune responses seem to play a central role. The emergence of new single-cell methods for quantification of antigen-specific T-cells directly ex vivo has prompted us to measure frequencies of MV-specific memory T-cells. As an indicator for T-cell activation IFN-gamma production was measured. PBMC were analysed by intracellular staining and ELISPOT assay after stimulation with MV-infected autologous B-lymphoblastoid cell lines or dendritic cells. T-cell responses were exclusively seen with PBMC from MV-seropositive healthy adults with a history of natural measles in childhood. The median frequency of MV-specific T-cells was 0.35% for CD3(+)CD4(+) and 0.24% for the CD3(+)CD8(+) T-cell subset. These frequencies are comparable with T-cell numbers reported by other investigators for persistent virus infections such as Epstein-Barr virus, cytomegalovirus or human immunodeficiency virus. Hence, this study illustrates that MV-specific CD4(+) and CD8(+) T-cells are readily detectable long after the acute infection, and thus are probably contributing to long-term immunity. Furthermore, this new approach allows efficient analysis of T-cell responses from small samples of blood and could therefore be a useful tool to further elucidate the role of cell-mediated immunity in measles as well as in other viral infections.

Adult↗

PubMed2000

Elevated intraluminal pressure inhibits vascular tissue plasminogen activator secretion and downregulates its gene expression.

We recently discovered that patients with essential hypertension have a markedly impaired capacity for stimulated release of tissue plasminogen activator (tPA) from vascular endothelium. This defect may reduce the chance of timely spontaneous thrombolysis in case of an atherothrombotic event. We now investigated whether increased intraluminal pressure as such may depress vascular tPA release or downregulate its gene expression. Segments of human umbilical veins were studied in a new computerized vascular perfusion model under steady laminar flow conditions for 3 or 6 hours. Paired segments were perfused at high or physiological intraluminal pressure (40 versus 20 mm Hg) under identical shear stress (10 dyne/cm(2)). Quantitative immunohistochemical evaluation of cellular tPA immunoreactivity was performed on paraffin-embedded 5-microm vascular sections. tPA mRNA in endothelial cells was quantified with reverse transcription real-time TaqMan polymerase chain reaction with GAPDH as endogenous control. Secretion of tPA into perfusion medium was evaluated with SDS-PAGE and Western blotting, followed by densitometric quantification. High-pressure perfusion downregulated tPA gene expression with a 38% decrease in tPA mRNA levels (P=0.01) compared with vessels perfused under normal intraluminal pressure. tPA release into the perfusion medium was markedly suppressed by high pressure (P<0.01 ANOVA). The intracellular storage pool of tPA was reduced after 6 but not 3 hours. Thus, elevated intraluminal pressure downregulates tPA gene and protein expression and inhibits its release from the endothelium independently of shear stress. The defective capacity for stimulated tPA release that we demonstrated in patients with essential hypertension might thus be an effect of the elevated intraluminal pressure per se.

Blood Pressure↗

PubMed2006

Differential expression of genes encoding tight junction proteins in colorectal cancer: frequent dysregulation of claudin-1, -8 and -12.

BACKGROUND AND AIMS: As integral membrane proteins, claudins form tight junctions together with occludin. Several claudins were shown to be up-regulated in various cancer types. We performed an expression analysis of genes encoding tight junction proteins to display differential gene expression on RNA and protein level and to identify and validate potential targets for colorectal cancer (CRC) therapy. PATIENTS AND METHODS: Amplified and biotinylated cRNA from 30 microdissected CRC specimen and corresponding normal tissues was hybridized to Affymetrix U133set GeneChips. Quantification of differential protein expression of claudin-1, -8 and -12 between normal and corresponding tumour tissues was performed by Western blot analyses. Paraffin-embedded CRC tissue samples, colon cancer cell lines and normal tissue microarray were analysed for protein expression of claudin-1 by immunohistochemistry (IHC). RESULTS: Claudin-1 (CLDN1) and -12 (CLDN12) are frequently overexpressed in CRC, whereas claudin-8 (CLDN8) shows down-regulation in tumour tissue on RNA level. Quantification of proteins confirmed the overexpression of claudin-1 in tumour tissues, whereas changes of claudin-8 and -12 were not significantly detectable on protein level. IHC confirmed the markedly elevated expression level of claudin-1 in the majority of CRC, showing membranous and intracellular vesicular staining. CONCLUSIONS: Differential expression of genes encoding claudins in CRC suggests that these tight junction proteins may be associated to and involved in tumorigenesis. CLDN1 is frequently up-regulated in large proportion of CRC and may represent potential target molecule for blocking studies in CRC.

Aged↗

PubMed2003

Mechanisms of staurosporine induced apoptosis in a human corneal endothelial cell line.

BACKGROUND: Apoptosis very probably plays a key part in endothelial cell loss during corneal storage in organ culture as well as hypothermic storage. However, the mechanisms underlying endothelial apoptosis are poorly understood. The response of a human corneal endothelial cell (HCEC) line to staurosporine, a known inducer of apoptosis, was investigated to gain insights into the intracellular modulators that participate in endothelial cell death. METHODS: Immortalised HCECs were studied after 3, 6, 12, and 24 hours of incubation with 0.2 micro M staurosporine. Cell shedding was monitored. Hoechst 33342 fluorescent DNA staining combined with propidium iodide was used for apoptosis/necrosis quantification and morphological examination. The caspase-3 active form was assessed using western blot, proteolytic activity detection, and immunocytochemistry. The cleaved form of poly(ADP-ribose) polymerase (PARP) was assessed using immunocytochemistry and western blot. The ultrastructural features of cells were screened after 12 hours with staurosporine or vehicle. RESULTS: The specific apoptotic nature of staurosporine induced HCEC death was confirmed. The ultrastructural features of staurosporine treated cells were typical of apoptosis. HCEC shedding and DNA condensation increased with time. Caspase-3 activity was detected as early as 3 hours after exposure with staurosporine, peaking at 12 hours of incubation. The presence of cleaved PARP after 3 hours confirmed caspase-3 activation. CONCLUSIONS: These data suggest strongly that HCEC cell death induced by staurosporine is apoptosis. The main consequence of HCEC apoptosis is shedding. Staurosporine induced apoptosis of endothelial cells involves activation of caspase-3, and could be a useful model to study strategies of cell death inhibition.

Apoptosis↗

PubMed2003

[A new membrane-permeable peptide from human].

OBJECTIVE: To study the translocation ability of a new protein domain (Circadian locomotor output cycles kaput protein's DNA-binding peptide, hCLOCK's DNA_BIND) from human through the membrane. METHOD: hCLOCK's DNA_BIND, which was chemically synthesized and labeled with FITC at N-terminal, was incubated with the vascular endothelial cell (ECV-304) and primary culture neuroglial cells in the culture medium, the distribution of it was observed on a fluorescence microscope. RESULT: hCLOCK's DNA_BIND has the ability to translocate through the cell membrane and accumulate in the nucleus. The quantification of cellular uptake of it increases with the increase of incubation time and concentration. However, the peptide was internalized at 4 degrees C as efficiently as that at 37 degrees C. CONCLUSION: It is promising to provide a new safe carrier for the intracellular treatment.

Cell Membrane↗

PubMed2004

In vivo monitoring of intracellular expression of human interleukin-2 using green fluorescent protein fusion partner in Pichia pastoris.

The use of Pichia pastoris for protein production was simplified by creation of fusion proteins containing green fluorescent protein (GFP) and the product of interest. Human interleukin-2 (hIL-2) was used as a model product: GFP enabled clear identification of fusion protein expression and, more importantly, the quantification of hIL-2. Although GFP fusions for bioprocess monitoring have been demonstrated in other hosts, this is its first use in P. pastoris.

Biotechnology↗

PubMed2004

Fast quantification of water in single living cells by near-infrared microscopy.

We have set up a near-infrared microscope using a tuneable diode laser in the range from 1530 to 1570 nm. This spectral range is close to the peak of the water overtone absorption. We used this new microscope to study liver cells, hepatocytes, showing that quantitative information of the intracellular water concentration in living cells can be extracted.

Absorption↗

PubMed2004

Quantification of optison bubble size and lifetime during sonication dominant role of secondary cavitation bubbles causing acoustic bioeffects.

Acoustic cavitation has been shown to deliver molecules into viable cells, which is of interest for drug and gene delivery applications. To address mechanisms of these acoustic bioeffects, this work measured the lifetime of albumin-stabilized cavitation bubbles (Optison) and correlated it with desirable (intracellular uptake of molecules) and undesirable (loss of cell viability) bioeffects. Optison was exposed to 500 kHz ultrasound (acoustic pressures of 0.6-3.0 MPa and energy exposures of 0.2-200 J/cm2) either with or without the presence of DU145 prostate cancer cells (10(6) cells/ml) bathed in calcein, a cell-impermeant tracer molecule. Bubble lifetime was determined using a Coulter counter and flow cytometer, while bioeffects were evaluated by flow cytometry. The lifetime of Optison cavitation nuclei was found to decrease and bioeffects (molecular uptake and loss of cell viability) were found to increase with increasing acoustic energy exposure. These bioeffects correlated well with the disappearance of bubbles, suggesting that contrast agent destruction either directly or indirectly affected cells, probably involving unstabilized cavitation nuclei created upon the destruction of Optison. Because Optison solutions presonicated to destroy all detectable bubbles also caused significant bioeffects, the indirect mechanism involving secondary cavitation bubbles is more likely.

Acoustics↗

PubMedDate not supplied

Entamoeba histolytica: correlation of assessment methods to measure erythrocyte digestion, and effect of cysteine proteinases inhibitors in HM-1:IMSS and HK-9:NIH strains.

Entamoeba histolytica trophozoites are able to degrade human erythrocytes; the loss of erythrocyte cellular matrix and degradation of plasma membrane were observed, along with the decrease in the average size of digestive vacuoles. Ninety-six percent of hemoglobin ingested was hydrolyzed by trophozoites within 3h, as evidenced by electrophoresis. Accordingly, X-ray spectroscopy revealed the presence of iron inside vacuoles after erythrophagocytosis, the concentration of which decreased to control levels in a similar period. Quantification of erythrocyte digestion at the early and late periods was determined by a spectrophotometric procedure, with t(1/2)=1.67 h and 35-min for HM-1:IMSS and HK-9:NIH trophozoites, respectively. In the latter, activity was due to the combined action of intracellular enzymatic activity and exocytosis. E-64c and leupeptin totally inhibited erythrocyte digestion within a 3-h period, thereafter hydrolysis took place at lower rate. Our results suggest that erythrocyte digestion in E. histolytica proceeds in different ways in these two amebic strains, and can be blocked by proteinase inhibitors.

Animals↗

PubMed2006

Streptococcus gordonii utilizes several distinct gene functions to recruit Porphyromonas gingivalis into a mixed community.

Dental plaque biofilm formation proceeds through a developmental pathway initiated by the attachment of pioneer organisms, such as Streptococcus gordonii, to tooth surfaces. Through a variety of synergistic interactions, pioneer organisms facilitate the colonization of later arrivals including Porphyromonas gingivalis, a potential periodontal pathogen. We have investigated genes of S. gordonii required to support a heterotypic biofilm community with P. gingivalis. By screening a plasmid integration library of S. gordonii, genes were identified that are crucial for the accumulation of planktonic P. gingivalis cells into a multispecies biofilm. These genes were further investigated by specific mutation and complementation analyses. The biofilm-associated genes can be grouped into broad categories based on putative function as follows: (i) intercellular or intracellular signalling (cbe and spxB), (ii) cell wall integrity and maintenance of adhesive proteins (murE, msrA and atf), (iii) extracellular capsule biosynthesis (pgsA and atf), and (iv) physiology (gdhA, ccmA and ntpB). In addition, a gene for a hypothetical protein was identified. Biofilm visualization and quantification by confocal microscopy confirmed the role of these genes in the maturation of the multispecies community, including biofilm architectural development. The results suggest that S. gordonii governs the development of heterotypic oral biofilms through multiple genetic pathways.

Bacterial Adhesion↗

PubMed2001

Noninvasive quantification of total sodium concentrations in acute reperfused myocardial infarction using 23Na MRI.

The transport of sodium and potassium between the intra- and extracellular pools and the maintenance of the transmembrane concentration gradients are important to cell function and integrity. The early disruption of the sodium pump in myocardial infarction in response to the exhaustion of energy reserves following ischemia and reperfusion results in increased intracellular (and thus total) sodium levels. In this study a method for noninvasively quantifying myocardial sodium levels directly from sodium (23Na) MRI is presented. It was used to measure total myocardial sodium on a clinical 1.5T system in six normal dogs and five dogs with experimentally-induced myocardial infarction (MI). The technique was validated by comparing total sodium content measured by 23Na MRI with that measured by atomic absorption spectrophotometry (AAS) in biopsied tissue. Total sodium measured by 23Na MRI was significantly elevated in regions of infarction (81.3 +/- 14.3 mmol/kg wet wt, mean +/- SD) compared to noninfarcted myocardial tissue from both infarcted dogs (36.2 +/- 1.1, P < 0.001) and from normal controls (34.4 +/- 2.8, P < 0.0001). Myocardial tissue sodium content as measured by 23Na MRI did not vary regionally in the lateral, anterior, or inferior regions in normal hearts (ANOVA, P = NS). Sodium content measured by 23Na MRI agreed with the mean AAS estimates of 31.3 +/- 5.6 mmol/kg wet wt (P = NS) in normal hearts, and did not differ significantly from AAS measurements in MI (P = NS). Thus, local tissue sodium levels can be accurately quantified noninvasively using 23Na MRI in normal and acutely reperfused MI. The detection of regional myocardial sodium elevations may help differentiate viable from nonviable, infarcted tissue.

Animals↗

PubMed1997

Regulation of expression of two different transcripts of the NF-1 gene in neuroblastoma.

Neurofibromin, the gene product of the NF-1 gene is expressed in two isoforms. The m-RNA of NF-1 type II contains an insertion of 63 bases in the so called GAP-related domain, that distinguishes it from the type I transcript. By sequence homology neurofibromin is supposed to have a similar function in regulating activity of ras in intracellular signal transduction as the GTPase activating protein (GAP). Both transcripts of NF-1 are simultaneously expressed in different molar ratio in neuroblastoma tumors. 1) We examined 9 different neuroblastoma cell lines for the ratio of expression of NF-1 type I and type II. For quantification of the two transcripts we performed RT-PCR of the m-RNA of the neuroblastoma cells using primers designed to cover the GAP-related domain. We found values ranging from a more than 3-fold excess of type I transcript in the cell line Kelly to a slight excess of the type II transcript (I/II = 0.6) in the cell line IMR 5. 2) As there are indications that expression of NF-1 type II is related to the state of differentiation, we tried to shift expression of NF-1 from type I to type II by treatment of the neuroblastoma cells with retinoic acid. Treatment of Kelly cells with 5 microM retinoic acid for 24 h already lowered the excess of the type I transcript from 3-fold to an only 1.6-fold excess. An inversion of the molar ratio from an excess of the type I transcript to an excess of type II transcript would enable to investigate the different role of the two transcripts in the regulation of ras-activity and differentiation.

Antineoplastic Agents↗

PubMed1988

Dependence of metabolic and structural heterogeneity of cholesterol ester-rich very low density lipoproteins on the duration of cholesterol feeding in rabbits.

Cholesterol ester-rich (CER) VLDL accumulate rapidly in the plasma of rabbits fed cholesterol-enriched diets. However, the major loci of enhanced synthesis of subfractions of CER-VLDL, their interaction with macrophages, and their relative contribution to atherogenesis have not yet been elucidated. To determine whether anabolism is hepatic or intestinal, subfractions of CER-VLDL were characterized at selected intervals from day 0 to 60 of cholesterol feeding. Rate zonal ultracentrifugation of CER-VLDL from rabbits fed cholesterol for 4 and 60 d demonstrated an early increase of the proportion of cholesterol carried in the intestinally-derived fraction (designated as Fx-I) of VLDL compared with that in hepatically-derived particles (Fx-H). Quantification by size exclusion HPLC also demonstrated that Fx-I was a prominent CER-VLDL component at day 4, while Fx-H particles became increasingly prominent with further cholesterol feeding. At both 4 and 60 d Fx-I stimulated cholesterol esterification and intracellular cholesterol content in macrophages more than the corresponding Fx-H did. In fact, Fx-H harvested at 4 d produced no cholesterol ester deposition. In contrast, Fx-H harvested at 60 d markedly stimulated cholesterol esterification and intracellular cholesterol content. Thus, both compositional and metabolic characteristics of CER-VLDL changed as a function of the duration cholesterol feeding.

Animals↗

PubMed1989

Radiochemical diagnosis of adrenal disease.

The adrenal gland consists of cortical and medullary components, both of which may be functionally imaged using radiopharmaceuticals designed to take advantage of the specialized physiology of each tissue. Radiolabeled cholesterol derivatives are taken up by normal and abnormal adrenal cortex and provide an in vitro map of adrenocortical function in Cushing's Syndrome, hyperaldosteronism, and hyperadrenogenism. Quantification of uptake shows strong correlation with biochemical parameters of adrenocortical hyperfunction. In the case of incidentally discovered euadrenal masses scintigraphy may help to distinguish between benign, nonfunctional cortical adenomas, and destructive, potentially malignant lesions. Radiolabeled metaiodobenzylguanidine (MIBG) is a tracer of type I uptake and intracellular storage capacity for catecholamines in sympathomedullary tissues and tumors derived from this system. This permits the location of pheochromocytomas of all types (benign and malignant, intra- and extra-adrenal, sporadic and familial) as well as neuroblastomas in all stages. Other neuroendocrine tumors with type I uptake capacity may also be imaged. In suitable cases preliminary data suggests the administration of large doses of MIBG may permit internal radiotherapy of otherwise untreatable neuroendocrine tumors.

Adrenal Gland Diseases↗

PubMed2006

Subcellular localization of nicotinamide adenine dinucleotide phosphate oxidase subunits in neurons and astroglia of the rat medial nucleus tractus solitarius: relationship with tyrosine hydroxylase immunoreactive neurons.

Superoxide produced by the enzyme nicotinamide adenine dinucleotide phosphate (NADPH) oxidase mediates crucial intracellular signaling cascades in the medial nucleus of the solitary tract (mNTS), a brain region populated by catecholaminergic neurons, as well as astroglia that play an important role in autonomic function. The mechanisms mediating NADPH oxidase (phagocyte oxidase) activity in the neural regulation of cardiovascular processes are incompletely understood, however the subcellular localization of superoxide produced by the enzyme is likely to be an important regulatory factor. We used immunogold electron microscopy to determine the phenotypic and subcellular localization of the NADPH oxidase subunits p47(phox), gp91(phox,) and p22(phox) in the mNTS in rats. The mNTS contains a large population of neurons that synthesize catecholamines. Significantly, catecholaminergic signaling can be modulated by redox reactions. Therefore, the relationship of NADPH oxidase subunit labeled neurons or glia with respect to catecholaminergic neurons was also determined by dual labeling for the superoxide producing enzyme and tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. In the mNTS, NADPH oxidase subunits were present primarily in somatodendritic processes and astrocytes, some of which also contained TH, or were contacted by TH-labeled axons, respectively. Immunogold quantification of NADPH oxidase subunit localization showed that p47(phox) and gp91(phox) were present on the surface membrane, as well as vesicular organelles characteristic of calcium storing smooth endoplasmic reticula in dendritic and astroglial processes. These results indicate that NADPH oxidase assembly and consequent superoxide formation are likely to occur near the plasmalemma, as well as on vesicular organelles associated with intracellular calcium storage within mNTS neurons and glia. Thus, NADPH oxidase-derived superoxide may participate in intracellular signaling pathways linked to calcium regulation in diverse mNTS cell types. Moreover, NADPH oxidase-derived superoxide in neurons and glia may directly or indirectly modulate catecholaminergic neuron activity in the mNTS.

Animals↗

PubMed2003

Clinical and technical evaluation of the ACS:OV serum assay and comparison with three other CA125-detecting assays.

BACKGROUND: In this study the clinical and technical performance of the CA125- detecting Bayer ACS:OV immunoluminometric serum assay was compared with three other well-established CA125-detecting assays. METHODS: A total of 1112 serum samples was included in this evaluation: 462 from apparently healthy women, 153 from patients with benign ovarian disease, 163 from patients with malignant ovarian disease, 10 from patients with borderline ovarian malignancies and 78 samples from 12 ovarian cancer patients during monitoring of disease. Serum samples from women with malignant endometrial (n = 68) and colon (n = 32) diseases were also included. Moreover, serum samples from women with benign uterine disease and endometriosis (n = 136) plus 10 serum samples from men (n = 7) and women (n = 3) with human anti-mouse antibodies (HAMA) after immunoscintigraphy were included. All samples were tested in duplicate with the Bayer ACS:OV, the Centocor CA125 II, the Abbott IMx CA125 and the Roche (formerly Boehringer Mannheim) Enzymun-Test CA125 II assays. RESULTS: The clinical performance of the Bayer ACS:OV assay, assessed in various patient groups, was similar to that of the two other automated assays. In serum from patients with benign diseases the highest values were found in patients with benign ovarian tumours. In the ovarian cancer patients followed during the course of disease we found similar marker patterns with all four assays. In contrast to the Roche Enzymun-CA125 II assay and to a lesser extent the Centocor CA125 II assay, the Bayer ACS:OV assay was less sensitive to interference from HAMA. CONCLUSION: The Bayer ACS:OV assay is a precise and reliable test for the quantification of CA125 in serum.

Biomarkers, Tumor↗

PubMed1986

Quantification of membrane properties of trigeminal root ganglion neurons in guinea pigs.

Passive and active (voltage- and time-dependent) membrane properties of trigeminal root ganglion neurons of decerebrate guinea pigs have been determined using frequency-domain analyses of small-amplitude perturbations of membrane voltage. The complex impedance functions of trigeminal ganglion neurons were computed from the ratios of the fast Fourier transforms of the intracellularly recorded voltage response from the neuron and of the input current, which had a defined oscillatory waveform. The impedance magnitude functions and corresponding impedance locus diagrams were fitted with various membrane models such that the passive and active properties were quantified. The complex impedances of less than one-quarter of the 105 neurons which were investigated extensively could be described by the complex impedance function for a simple RC-electrical circuit. In such neurons, the voltage responses to constant-current pulses, using conventional bridge-balance techniques, could be fitted with single exponential curves, also suggesting passive membrane behavior. A nonlinear least-squares fit of the complex impedance function for the simple model to the experimentally observed complex impedance yielded estimates of the resistance of the electrode, and of input capacitance (range, 56 to 490 pF) and input resistance (range, 0.8 to 30 M omega) of the neurons. The majority of trigeminal ganglion neurons were characterized by a resonance in the 50- to 250-Hz bandwidth of their impedance magnitude functions. Such neurons when injected with "large" hyperpolarizing current pulses using bridge-balance techniques showed membrane voltage responses that "sagged" (time-dependent rectification). Also, repetitive firing commonly occurred with depolarizing current pulses; this characteristic of neurons with resonance in their impedance magnitude functions was not observed in neurons with "purely" passive membrane behavior. A nonlinear least-squares fit of a five-parameter impedance fitting function based on a membrane model to the impedance locus diagram of a neuron with resonance yielded estimates of its membrane properties: input capacitance, the time-invariant part of the conductance, the conductance activated by the small oscillatory input current, and the relaxation time constant for this conductance. The ranges of the estimates for input capacitance and input resistance were comparable to the ranges of corresponding properties derived for neurons exhibiting "purely" passive behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗