Biomedical subjects

S Fan

Publications and source records attributed to S Fan.

At least 127 records · Page 7Linked to original sources

PubMed1995

Relationships between G1 arrest and stability of the p53 and p21Cip1/Waf1 proteins following gamma-irradiation of human lymphoma cells.

We investigated temporal relationships between ionizing radiation-induced G1 arrest and induction of the p53-regulated genes GADD45, CIP1/WAF1, and MDM2 in a series of Burkitt's lymphoma and lymphoblastoid cell lines that differed in p53 gene status. Emphasis was placed on characterization of the EW36 cell line, which despite expressing wild-type p53 genes, is defective in G1 arrest following gamma-irradiation (P. M. O'Connor et al., Cancer Res., 53: 4776-4780, 1993). Induction of CIP1/WAF1, GADD45, and to a lesser extent MDM2 mRNA was observed in all wild-type p53 lines that arrested in G1. Cell lines that contained only mutant p53 genes or were heterozygous for p53 mutations failed to induce appreciable levels of these p53-regulated transcripts and did not arrest in G1. G1 arrest in the wild-type p53 cell line WMN was more prolonged than elevation of CIP1/WAF1, GADD45, or MDM2 transcripts, suggesting that G1 arrest duration must be dependent upon stability of these newly synthesized proteins. In agreement, we found that p21Cip1/Waf1, a potent inhibitor of G1-S phase cyclin-dependent kinases, was maintained at elevated levels throughout the period that WMN cells remained arrested in G1. EW36 cells exhibited normal induction of CIP1/WAF1, GADD45, and MDM2 mRNA following gamma-irradiation, suggesting that the defect in G1 arrest must reside downstream of p53 transactivation. Investigations into the stability of p53 and p21Cip1/Waf1 revealed that EW36 cells failed to maintain elevated levels of these proteins following irradiation. p53 levels decreased within 4 h of irradiation, and p21Cip1/Waf1 levels decreased shortly after the normal decline of CIP1/WAF1 mRNA levels. Degradation of p21Cip1/Waf1 coincided with the escape of EW36 cells from G1 arrest. Our studies suggest that p21Cip1/Waf1 stability may determine G1 arrest duration and that premature degradation of this protein could provide an alternative route to subversion of the G1 checkpoint in cancer cells.

Burkitt Lymphoma↗

PubMed1995

Study of the role of retinoblastoma protein in terminal differentiation of murine erythroleukemia cells.

Hexamethylenebisacetamide-induced terminal differentiation of Friend virus-transformed murine erythroleukemia (MEL) cells can be inhibited by okadaic acid, an inhibitor of type 1 and type 2A protein phosphatases. The inhibition is shown to be correlated with prevention of dephosphorylation of retinoblastoma protein (pRB) in cells and bypass of G1 prolongation in the cell cycle. These results suggest that pRB-mediated G1 prolongation is necessary for MEL cells to commit to terminal differentiation. However, further experiments demonstrate that the simple cell cycle exit is not sufficient for commitment to terminal differentiation. Induction of dephosphorylation of pRB and subsequent G1 prolongation by forskolin does not lead MEL cells to differentiate. Additional pRB has been expressed in MEL cells by transfection with a neo-resistant plasmid containing RB cDNA under the control of a cytomegalovirus promoter. Exogenously expressed pRB is hyperphosphorylated in logarithmically growing MEL cells without any noticeable change in growth rate between the transfected cell line and the parental cell line. This result suggests that pRB in MEL cells is regulated by protein kinases and protein phosphatases and not by transcription.

Acetamides↗

PubMed1995

Disruption of p53 function sensitizes breast cancer MCF-7 cells to cisplatin and pentoxifylline.

The possibility that appropriately designed chemotherapy could act selectively against p53-defective tumor cells was explored in MCF-7 human breast cancer cells. These cells were chosen because they have normal p53 function but are representative of a tumor cell type that does not readily undergo p53-dependent apoptosis. Two sublines (MCF-7/E6 and MCF-7/mu-p53) were established in which p53 function was disrupted by transfection with either the human papillomavirus type-16 E6 gene or a dominant-negative mutant p53 gene. p53 function in MCF-7/E6 and MCF-7/mu-p53 cells was defective relative to control cells in that there were no increases in p53 or p21Waf1/Cip1 protein levels and no G1 arrest following exposure to ionizing radiation. Survival assays showed that p53 disruption sensitized MCF-7 cells to cisplatin (CDDP) but not to several other DNA-damaging agents. CDDP sensitization was not limited to MCF-7 cells since p53 disruption in human colon carcinoma RKO cells also enhanced sensitivity to CDDP. Contrary to the other DNA-damaging agents tested, CDDP-induced DNA lesions are repaired extensively by nucleotide excision, and in agreement with a defect in this process, MCF-7/E6 and MCF-7/mu-p53 cells exhibited a reduced ability to repair a CDDP-damaged chloramphenicol acetyltransferase-reporter plasmid transfected into the cells. Therefore, we attributed the increased CDDP sensitivity of MCF-7 cells with disrupted p53 to defects in G1 checkpoint control, nucleotide excision repair, or both. The G2 checkpoint inhibitor pentoxifylline exhibited synergism with CDDP in killing MCF-7/E6 cells but did not affect sensitivity of the control cells. Moreover, pentoxifylline inhibited G2 checkpoint function to a greater extent in MCF-7/E6 than in the parental cells. These results suggested that, in the absence of p53 function, cancer cells are more vulnerable to G2 checkpoint abrogators. Our results show that a combination of CDDP and pentoxifylline is capable of synergistic and preferential killing of p53-defective tumor cells that do not readily undergo apoptosis.

Apoptosis↗

PubMed1995

A mutant p21 cyclin-dependent kinase inhibitor isolated from a Burkitt's lymphoma.

The growth arrest mediated by p53 is caused at least in part by the p53 mediated expression of p21 (p21waf1/Cip1). Since only one-third of primary Burkitt's lymphomas (BL) demonstrate mutations in the p53 gene, we examined the structural integrity of the p21 coding region by single-strand conformational polymorphism and DNA sequence analysis to determine the extent to which this gene is mutated in BL. Of 34 BLs analyzed, a frequent change (38%) at codon 31 that replaced Ser with Arg was found in 13 samples, 10 of which were from Africa. This change at codon 31 is also detected in peripheral blood DNA from normal subjects and may thus represent a polymorphism. One BL cell line, DH978, carried a change at codon 63: Phe to Leu. This mutation was heterozygous, and both the wild-type and the mutated p21 mRNA were expressed in the tumor cell line. By transfection experiments, the mutant p21 was less efficient in suppressing clonogenicity than wild-type p21. To our knowledge, this is the only mutation described in p21. The availability of this mutant p21 should further help in functional studies of p21.

Base Sequence↗

PubMed1995

Selective sensitivity of macrophages to cytotoxicity by inhibitors of macromolecular synthesis: induction of apoptosis.

Initial studies designed to measure the effect of inhibiting RNA synthesis by dactinomycin on macrophage functions revealed that the cells were uniformly killed at concentrations that have been routinely used to inhibit RNA synthesis in other cell types. We, thus, determined the dose curve for the cytotoxicity of dactinomycin for macrophages and two other cell types, L929 cells and splenic lymphocytes. Macrophages were extremely sensitive to the cytotoxicity of dactinomycin compared to the other cell types. Submicromolar concentrations that induced 100% cytotoxicity in macrophages caused little death in L929 cells or lymphocytes. Concentrations of dactinomycin that inhibited RNA synthesis by 40% in macrophages induced almost complete cell death but inhibition of over 80% of RNA synthesis in L929 cells or lymphocytes induced no measurable cytotoxicity. Macrophages did take up more dactinomycin than other cells but the amount was not sufficient to account for the large differences in cytotoxicity. We next tested the effects of doxorubicin and cycloheximide and found that macrophages were also extremely sensitive to killing by these compounds, and there was a very close association between the amount of inhibition of protein synthesis and the amount of toxicity. The morphology of macrophages exposed to these agents was consistent with death by apoptosis. This was further supported by assays measuring membrane integrity and DNA fragmentation. These data demonstrate that inhibition of macromolecular synthesis in macrophages, by different mechanisms, causes macrophages to undergo apoptosis. They further suggest that, in contrast to other cell types that require protein synthesis for apoptosis, macrophages require the synthesis of certain proteins to avoid apoptosis.

Animals↗

PubMed1995

Avoiding acyclovir neurotoxicity in patients with chronic renal failure undergoing haemodialysis.

Acute neurotoxicity following the administration of the recommended oral dose of acyclovir (800 mg twice daily) to dialysis-dependent patients is increasingly recognised. This suggests that the recommended dose is too high. Little is known of the pharmacokinetics of oral acyclovir in dialysis patients. We studied 7 patients with oliguric end stage renal failure receiving haemodialysis. Following haemodialysis, each patient received a single 800-mg tablet of acyclovir. Plasma acyclovir levels were monitored over the next 48 h as well as before and after the next routine dialysis. Peak plasma levels were achieved at 3 h (12.54 +/- 1.76 microM, range 8.5-17.5 microM) with the half-life calculated to be 20.2 +/- 4.6 h. Mean plasma level of 6.29 +/- 0.94 microM were within the quoted range to inhibit herpes zoster virus (4-8 microM) at 18 h. Haemodialysis (4-5 h) eliminated 51 +/- 11.5% of the acyclovir which remained at 48 h. Computer modelling of various dose modifications suggests that a loading dose of 400 mg and a maintenance dose of 200 mg twice daily is sufficient to maintain a mean plasma acyclovir level of 6.4 +/- 0.8 microM. A further loading dose (400 mg) after dialysis would raise the residual acyclovir concentration by 6.1 +/- 1.0 microM. Such a dose modification should prevent neurotoxicity, whilst the rapid elimination of acyclovir by a single haemodialysis treatment provides both a diagnostic and therapeutic tool when toxicity is suspected.

Acyclovir↗

PubMed1995

Biodegradation of sorbed chemicals in soil.

Rates of biodegradation of sorbed chemicals are usually lower in soil than in aqueous systems, in part because sorption reduces the availability of the chemical to microorganisms. Biodegradation, sorption, and diffusion occur simultaneously and are tightly coupled. In soil, the rate of biodegradation is a function of a chemical's diffusion coefficient, sorption partition coefficient, the distance it must diffuse from the site of sorption to microbial populations that can degrade it, and its biodegradation rate constant. A model (DSB model) was developed that describes biodegradation of chemicals limited in the availability by sorption and diffusion. Different kinetics expressions describe biodegradation depending on whether the reaction is controlled by mass transfer (diffusion and sorption) or the intrinsic biodegradation rate, and whether biodegradation begins during or after the majority of sorption has occurred. We tested the hypothesis that there is a direct relationship between how strongly a chemical is sorbed and the chemical's biodegradation rate. In six soils with different organic carbon contents, there was no relationship between the extent or rate of biodegradation and the sorption partition coefficient for phenanthrene. Aging of phenanthrene residues in soil led to a substantial reduction in the rate of biodegradation compared to biodegradation rates of recently added phenanthrene. Considerable research has focused on identification and development of techniques for enhancing in situ biodegradation of sorbed chemicals. Development of such techniques, especially those involving inoculation with microbial strains, should consider physical mass transfer limitations and potential decreases in bioavailability over time.

Absorption↗

PubMed1995

[The design and application of speech signal processing system by computer in stomatology.].

In this study we established a computer bases on Speech Signal Processing System and changes of formant frequencies of the vowel/i/accompany the changes in the oral cavity after maxillary surgery and prosthodontic reconstruction.The study found the F1 for vowel/i/has no change,while the F2 peak significantly shifted between the preprosthetic and postprosthetic speaking condition after anterior resection of relative energy error value and the speech intelligible measured aurally(P<0.05).

English Abstract↗

PubMed1995

Varicella zoster virus infection after allogeneic or autologous hemopoietic stem cell transplantation.

A retrospective study was carried out in 161 patients who underwent allogeneic or autologous hemopoietic stem cell transplants. The aim was to determine the frequency, outcome and risk-factors associated with varicella zoster virus (VZV) infection. Post-transplant VZV infection occurred in 29 patients. The median onset of infection was 6.5 months post-transplant, with 82% of cases occurring within the first year. Localized herpes zoster was seen in 27 patients, one patient had varicella, and one patient had simultaneous presentation of both herpes zoster and varicella. No cutaneous or visceral dissemination was noted in the series. Each patient was treated with intravenous acyclovir. Mild complications with postherpetic neuralgia were reported by three patients. There were no deaths from VZV infection. Two risk factors noted to be associated with VZV infection were the presence of graft-versus-host disease in allogeneic transplants and leukemia as the underlying disease in autologous transplants. The overall incidence of post-transplant VZV infection in the present series was relatively low compared with that of other reports involving either allogeneic or autologous bone marrow transplantation.

Adolescent↗

PubMed1995

[Clinical characteristics of hepatic tuberculosis].

The clinical characteristics of hepatic tuberculosis in 52 cases diagnosed pathologically were analyzed. Fever, abdominal pain and hepatomegaly were the major clinical manifestations; they were present in 96.2%, 42.3% and 88.5% of the patients respectively. The fever had no consistent pattern and the abdominal pain was usually localized to the right hypochondrium and not related to overwork. Hypergrammaglobulinaemia, elevated alkaline phosphatase level and increased ESR were noted in most of the patients (76.9%, 75.0%, 76.5% respectively). 62.5% of the 52 patients was diagnosed by percutaneous liver biopsy. Since there is no consistent clinical pattern in patients with hepatic tuberculosis, the diagnosis should be considered in patients with unexplained fever associated especially with hepatomegaly or hepatosplenomegaly, elevated alkaline phosphatase level, hypergrammaglobulinaemia and increased ESR, Liver biopsy is the most valuable method to confirm the diagnosis of hepatic tuberculosis.

Adolescent↗

PubMed1995

Cytogenetic studies in de novo acute nonlymphocytic leukemia.

BACKGROUND: There is currently considerable interest in the cytogenetic analysis of leukemia. The improvement of banding techniques has made it possible to rather precisely identify deletion, translocation, inversions, and other structural chromosome abnormalities. Specific recurring chromosome abnormalities associated with distinctive morphologic features are thus increasingly recognized in acute nonlymphocytic leukemia. For example, uneven geographic distribution of nonrandom specific chromosome aberrations has been reported. We herein report the results of chromosome studies on 30 Chinese patients with de novo acute nonlymphocytic leukemia. METHODS: Cytogenetic studies were performed at Veterans General Hospital-Taipei, from 1988 to 1993, on unselected samples of 30 patients with de novo acute nonlymphocytic leukemia. Chromosome analysis was performed by short-term culture techniques on bone marrow material obtained from patients at diagnosis. Metaphase chromosomes were banded by the conventional trypsin-Giemsa banding technique and then karyotyped according to the International System for Human Cytogenetic Nomenclature (ISCN). Classification of leukemia was based on the criteria of the French-American-British cooperative group. RESULTS: Of the 30 patients with adequate specimens, 17 (56%) demonstrated clonal chromosome abnormalities. Six patients were found to have structural rearrangements and seven patients have a numerical change as the sole abnormality. Four patients showed both structural and numerical anomalies. t(8;21) was found in 1 of the 8 M2 type ANLL patients and two of them had monosomy 21. Four of the 6 patients with acute promyelocytic leukemia (APL; M3 subtype) showed t(15;17). Two patients with M4 type leukemia and abnormal bone marrow eosinophils showed inv(16)(p13q22). One patient with M4 type leukemia demonstrated the loss of chromosome #7 and none showed the loss or deletion of chromosome #5. CONCLUSIONS: This study revealed a consistent finding of t(15;17) in APL; however, a low incidence of t(8;21), -5/5q- and -7/7q- in our patients demonstrated the possible difference in the incidence of chromosomal abnormalities in ANLL between the oriental peoples and the whites.

Adult↗

PubMed1995

Factors related to long-term effects of thymectomy on myasthenia gravis.

The authors report the results of long-term follow-up after thymectomy on 92 cases with myasthenia gravis (MG), including 22 cases of thymomatous MG. These patients were followed up for 6-73 months with an average of 23 months. The surgically effective rate was 88.0% and the late mortality, 6.5%. The sex of the patients and the durations of disease were not obviously related to the prognosis, however the effect of thymectomy was much better in patients aged 10-39 years than in other age groups. The modified Osserman's clinical classification, acetylcholine receptor (AchR) antibodies and citric acid extract (CAE) antibodies titers in plasma and pathological patterns of the surgical specimens of thymus including immunohistochemical observation play an important role among various factors related to the long-term effects.

Adolescent↗

PubMed1994

p53 gene mutations are associated with decreased sensitivity of human lymphoma cells to DNA damaging agents.

The present study assessed the role of the p53 tumor suppressor gene in cell cycle arrest and apoptosis following treatment of Burkitt's lymphoma and lymphoblastoid cell lines with gamma-rays, etoposide, nitrogen mustard, and cisplatin. Cell cycle arrest was measured by flow cytometry; p53 and p21Waf1/Cip1 protein levels were measured by Western blotting; cell survival was measured in 72-96-h growth inhibition assays and by trypan blue staining, and apoptotic DNA fragmentation was assessed by either agarose gel electrophoresis or a modified filter elution method. We found that gamma-rays and etoposide induced a strong G1 arrest in the wild-type p53 lines while nitrogen mustard and cisplatin induced relatively little G1 arrest. All agents failed to induce G1 arrest in cells containing mutant p53 genes. The degree of G1 arrest observed with these agents correlated with the rate of p53 and p21Waf1/Cip1 protein accumulation: gamma-rays and etoposide induced rapid accumulation of both p53 and p21Waf1/Cip1; nitrogen mustard and cisplatin induced slow accumulation of p53 and no major accumulation of the p21Waf1/Cip1 protein. Despite differences in G1 arrest and kinetics of p53 or p21Waf1/Cip1 protein accumulation, all agents tended to decrease survival to a greater extent in the wild-type p53 lines compared to the mutant p53 lines. Cell death in the wild-type p53 lines was associated with intracellular DNA degradation into oligonucleosomal sized DNA fragments, indicative of apoptosis. We also observed an inverse sensitivity relationship between nitrogen mustard/cisplatin and etoposide in the mutant p53 lines and this was found to correlate with topoisomerase II mRNA levels in the cells. Our results suggest that p53 gene status is an important determinant of both radio- and chemosensitivity in lymphoid cell lines and that p53 mutations are often associated with decreased sensitivity to DNA damaging agents.

Apoptosis↗

PubMed1994

Anti-AIDS agents. 15. Synthesis and anti-HIV activity of dihydroseselins and related analogs.

Forty-two dihydroseselins based on the structure of suksdorfin (1) were synthesized in order to evaluate their anti-HIV activity. These synthetic derivatives include 3',4'-di-O-acyl- and 3'- or 4'-O-acyl-cis-dihydroseselins (8-21) and 3',4'-trans-dihydroseselins with O-acyl and/or O-alkyl groups at the 3' and 4' positions (6, 22-43). Two 4'-azido (44, 45) and three 4'-alkylamido (46, 48, 49) derivatives were also prepared. By using optically pure reagents, three pairs of diastereoisomers were synthesized and separated as optically pure compounds (14, 15; 16, 17; 38, 39). Together with the above synthetic derivatives, seselin (3) and (+/-)-cis-(4), (+)-cis- (5), and (+/-)-trans-dihydroseselin-3',4'-diol (7) were also tested for their in vitro anti-HIV activity. An optically pure compound, 3',4'-di-O-(-)-camphanoyl-(+)-cis-khellactone (16), showed potent inhibitory activity and remarkable selectivity against HIV replication. The EC50 value and in vitro therapeutic index (TI) of 16 are 4 x 10(-4) microM and 136,719, respectively, which are better than those shown by AZT in the same assay. In addition, compound 16 is also active against HIV replication in a monocytic cell line and in peripheral blood mononuclear cells (PBMCs). Our in vitro assay indicated that, like compound 1, compound 16 is not an inhibitor of HIV-1 reverse transcriptase. Moreover, the anti-HIV activity of 16 is stereoselective as its three diastereoisomers (17, 38, 39) are at least 10,000 times less active. Since other synthetic dihydroseselin derivatives with different substituents or without any substituents are inactive or are active only at much higher concentration, the antiviral potency of 16 could be associated with the camphanoyl moieties of its structure. Therefore, compound 16 represents a unique coumarin structure with promising anti-HIV activity.

Acquired Immunodeficiency Syndrome↗

PubMed1994

CGRP in the serum of endotoxin-treated rats suppresses lymphoproliferation.

Mouse mesenteric lymph node cells were incubated with concanavalin A (Con A) with or without the rat form of calcitonin gene-related peptide (rCGRP) (0.1 fM-1 microM) +/- human (h)CGRP8-37 (1 microM) for 48 h. DNA synthesis was assessed by [3H]thymidine incorporation. Con A-stimulated DNA synthesis was suppressed by 13, 20, and 30% at 10 fM, 1 pM, and 100 pM of rCGRP, respectively. hCGRP8-37 (1 microM), a selective blocker of CGRP1 receptor, completely inhibited the suppression of DNA synthesis by rCGRP (10 fM-100 pM). rCGRP caused concentration-dependent elevations of cAMP levels, which were potentiated by pretreatment with 3-isobutyl-1-methylxanthine (0.3 mM, 10 min), an inhibitor of cAMP-phosphodiesterase. hCGRP8-37 (1 microM) significantly inhibited cAMP elevations induced by rCGRP at the lower concentrations, but not at the highest concentrations of rCGRP. These data suggest that rCGRP, at circulating levels (1-10 pM), appears to directly interact with receptors on mouse mesenteric lymph node cells that are coupled to cAMP generation, ultimately inhibiting lymphocyte proliferation. To test the involvement of CGRP in suppression of lymphocyte proliferation by serum from endotoxin-treated rats, mouse mesenteric lymph node cells were stimulated with Con A with or without dilutions of endotoxin treated rat serum. At a 1:20 dilution, DNA synthesis was suppressed 30%, at a 1:40 dilution, DNA synthesis was suppressed by 34%, and at a 1:80 dilution, DNA synthesis was suppressed 25%. At all serum dilutions, coincubation with hCGRP8-37 (1 microM) significantly inhibited the suppressive effect of the endotoxin treated rat serum. These data suggest that the immunosuppression observed during endotoxin shock may be due, at least in part, to CGRP in serum.

Animals↗

PubMed1994

Sources of attention-sensitive visual event-related potentials.

In a study of the neural processes that mediate visual attention in humans, 32-channel recordings of event-related potentials were obtained from 14 normal subjects while they performed a spatial attention task. The generator locations of the early C1, P1, and N1 components of the visual evoked response were estimated by means of topographic maps of voltage and current source density in conjunction with dipole modelling. The topography of the C1 component (ca. 85 ms post-stimulus) was consistent with a generator in striate cortex, and this component was unaffected by attention. In contrast, the P1 and N1 components (ca. 95 and 170 ms) exhibited current density foci at scalp sites overlying lateral extrastriate cortex and were larger for attended stimuli than for unattended stimuli. The voltage topographies in the 75-175 ms latency range were modeled with a 5-dipole configuration consisting of a single striate dipole and left-right pairs of dipoles located in lateral extrastriate and inferior occipito-temporal areas. This model was found to account for the voltage topographies produced by both attended and unattended stimuli with low residual variance. These results support the proposal that visual-spatial attention modulates neural activity in extrastriate visual cortex but does not affect the initial evoked response in striate cortex.

Adolescent↗

PubMed1994

Clinical observation of treatment of hypertension with calcium.

The effect of oral calcium supplementation (1000 mg/day) on hypertension was studied in 57 borderline and mild-to-moderate hypertensive patients in a randomized, double-blind, placebo-controlled study for 14 weeks. Twenty-five patients from the above groups (11 from the calcium-treated group and 14 from the placebo group) were studied in a crossover fashion for 14 more weeks. The high calcium intake lowered systolic blood pressure by 17 mm Hg (P < .01), and diastolic blood pressure by 11 mm Hg (P < .01). Fifty percent of the calcium-treated patients showed a significant antihypertensive effect and were termed calcium responders. In the crossover study, serum sodium was lower after taking calcium than after placebo intake (P < .05). Pretreatment plasma free calcium content of the calcium-responsive patients was significantly lower (P < .05) than in the calcium nonresponsive patients, and was highly significantly increased (P < .01) after administering calcium. The result showed that oral calcium supplementation can lower blood pressure in a significant fraction of essential hypertensive subjects, and that the free calcium level in plasma may help identify calcium-responsive individuals. While the mechanism by which increased calcium intake lowers blood pressure in hypertension is still undetermined, these data support an underlying relationship between hypertension and calcium and possibly sodium metabolism.

Administration, Oral↗

PubMed1994

Differences in voltage-dependent sodium currents exhibited by superficial and deep layer neurons of guinea pig entorhinal cortex.

1. Sodium currents were studied using whole-cell voltage-clamp techniques in neurons acutely isolated from superficial (II/III) and deep (V/VI) layers of guinea pig entorhinal cortex. 2. Sodium currents were larger (peak amplitude) in superficial than in deep layer cells under the same conditions: -1939 +/- 780 (SD) pA (N = 6) versus -307 +/- 257 pA (N = 6). Specific membrane conductance was calculated to be 12.3 +/- 9.6 mS/cm2 for superficial layer cells and 1.4 +/- 0.9 mS/cm2 for deep layer cells. 3. Sodium currents could be activated in superficial layer cells from potentials as depolarized as -20 mV, whereas no significant currents could be activated in deep neurons from potentials more depolarized than about -50 mV. Using a protocol consisting of a 25-ms prepulse and a 20 ms test pulse, the inactivation curves for superficial layer cells were found to be shifted toward more depolarized potentials by an average of 15 mV (V50 = -59.8 +/- 3.8 mV compared with -75.7 +/- 12.0 mV for deep cells). This produced a region of overlap with the activation curves for superficial cells. 4. Over a range of about -50 to -20 mV in superficial layer cells, the region of overlap of the activation and inactivation curves, a sodium current could be activated, which did not fully inactivate during the test pulse (average peak amplitude: -89.5 +/- 48.7 pA; crossover voltage: -39.2 +/- 2.0 mV). Voltage steps to more depolarized potentials, outside the voltage "window", permitted complete inactivation of the sodium current.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗