Alterations of Fas (APO-1/CD95) gene in transitional cell carcinomas of urinary bladder

Fas (Apo-1/CD95) is a cell-surface receptor involved in cell death signaling. The key role of the Fas system in negative growth regulation has been studied mostly within the immune system, and somatic mutations of Fas in cancer patients have been described solely in lymphoid-lineage malignancies. We analyzed somatic mutations and loss of heterozygosity of Fas gene in 43 transitional cell carcinomas of urinary bladder. Overall, 12 tumors (28%) were found to have Fas mutations, including 11 missense mutations and 1 frameshift mutation. Ten of the 12 mutations were located in the death domain known to be involved in the transduction of an apoptotic signal, and 8 of these 10 mutations showed an identical G to A transition at bp 993, indicating a potential hotspot in bladder cancers. Three of eight (38%) informative tumors carrying Fas mutations showed LOH at polymorphic sites in the promoter region. This is the first report on the Fas gene mutations in nonlymphoid malignancies, and our data suggest that alterations of the Fas gene might lead to the loss of its apoptotic function and contribute to the pathogenesis of some bladder cancers.

Downregulated gelsolin expression in hyperplastic and neoplastic lesions of the prostate

BACKGROUND

Because of its role in cell motility and growth regulation, gelsolin, an actin-binding protein, has been considered a tumor suppressor and a potential prognostic marker in some neoplasias, such as breast and bladder cancer. Little is known about its immunoexpression in prostatic adenocarcinoma (PCA).

METHODS

Formalin-fixed, paraffin-embedded tissues of 72 prostatectomy specimens with adenocarcinoma and 8 nonneoplastic prostates from autopsies were stained with a gelsolin monoclonal antibody using the Avidin-biotin-peroxidase complex (ABC) method after microwave antigen retrieval. Immunoreactivity was evaluated in PCA, prostatic intraepithelial neoplasia (PIN), benign prostatic hyperplasia (BPH), and nonproliferative glandular tissue and stroma. The results were statistically analyzed.

RESULTS

Consistent gelsolin immunoreactivity was seen in prostatic stromal cells, smooth muscle, endothelia, and nerves. Variable gelsolin expression was seen in 20-100% (average (A) = 65.5%) of glandular cells in nonproliferative tissue (N = 75); 0-50% (A = 9.7%) in BPH (N = 59); 0-80% (A = 8.9%) in PIN (N = 61); and 0-90% (A = 9.3%) in PCA (N = 71). The level of gelsolin expression in nonproliferative prostatic tissue was similar between prostates with PCA (A = 63.4%) and nonneoplastic prostates (A = 67.5%). The level of gelsolin expression did not correlate with age, tumor size, Gleason score, or stage.

CONCLUSIONS

Gelsolin is decreased in PCA, PIN, and BPH in comparison to nonproliferative tissue. The role of this downregulation in the development of PCA is not clear. The similar reduction seen in PIN and BPH suggests that this event takes place indiscriminately in hyperplasia and early tumorigenesis in the prostate, which might limit its prognostic significance in PCA.

Clinical and molecular biological analysis of a nosocomial outbreak of vancomycin-resistant enterococci in a neonatal intensive care unit

Vancomycin-resistant enterococci (VRE) have emerged as important nosocomial pathogens since 1988. We report here an outbreak of VRE between April 1997 and May 1997 in our neonatal intensive care unit (NICU). All isolates from four patients were identified as Enterococcus faecium positive and were resistant to vancomycin and teicoplanin. All of the patients with VRE were isolated for at least 5 d after admission to the unit and the positive cultures lasted between 13 and 31 d. There were no cases of sepsis or mortality in the patients with VRE. Two cases had previously received vancomycin therapy. All isolates were shown to have the vanA gene and had the same band pattern on repetitive PCR. After the four episodes, all equipment used to care for the patients were decontaminated and the staff engaged in therapy used disposable gloves and gowns. There were no more episodes. However, the NICU is no longer a safety area with regards to vancomycin-resistant enterococcal infection.

In vitro anticomplementary activity of hederagenin saponins isolated from roots of Dipsacus asper

Anticomplementary activity of hederagenin and related saponins isolated from Dipsacus asper was investigated in vitro. HN saponin F (3) was most potent with IC50 value of 3.7x10(-5) M followed by 3-O-beta-D-glucopyranosyl-(1->3)-alpha-L-rhamnopyranosyl-(1->2)-beta-L-+ ++arabi nopyranosyl hederagenin 28-O-beta-D-glucopyranosyl-(1->6)-beta-D-glucopyrano side (8), 3-O-beta-L-arabinopyranosyl hederagenin 28-O-beta-D-glucopyranosyl-(1->6)-beta-D-glucopyranoside (5), dipsacus saponin A (4), and hederagenin (1) on the classical pathway (CP) of complement system, while the saponins 3-5 did not show the inhibition of hemolysis and rather increase the hemolysis on the alternative pathway (AP). However, all of C-3 monodesmosides [prosapogenin CP (2), dipsacus saponin B (6), and dipsacus saponin C (7)] evoked hemolysis directly on the erythrocytes.

Sophoricoside analogs as the IL-5 inhibitors from Sophora japonica

Fruits of Sophora japonica L. (Leguminosae) exhibited an inhibitory effect in the IL-5 bioassay of mIL-5-dependent Y16 proliferation. The isoflavonoids of sophoricoside, genistein, orobol, and genistin were isolated as the IL-5 inhibitors from fresh fruits of the plant by activity-guided fractionation. Among the IL-5 inhibitors, sophoricoside exhibited the highest inhibitory effect with 89% inhibition at 12.5 microM, 82% at 6.3 microM, 72% at 3.1 microM, 59% at 1.6 microM, and 24% at 0.8 microM where the 50% inhibition (IC50) was shown at the concentration of 1.5 microM. Oxyphenylbutazone as the positive control exhibited the IC50 value at the concentration of 31.7 microM. In the order of IC50 values the inhibitory potency in the IL-5 bioassay was sophoricoside > orobol (9.8 microM) approximately equal to genistin (10.6 microM) > genistein (51.9 microM). The position of O-glycosylation and number of hydroxy groups in the isoflavonoids seem to play an important role in the inhibitory effect in the IL-5 bioassay.

Combinatorial mixture synthesis and biological evaluation of dihydrophenyl triazine antifolates

The traditional 'one-pot' three component synthesis was adapted successfully for combinatorial mixtures synthesis of dihydrophenyl triazines, which are nonclassical, dihydrofolate reductase (DHFR) inhibitors. Each library was designed to comprise eight reaction mixture pots and in every pot there were three dihydrophenyl triazines. A total of three libraries were synthesized and the final number of compounds harvested was 64. The products precipitated out of the reaction mixture and could be collected easily and cleansed by washing. Solid supports and further purification processes were not required. The reactions were monitored by TLC and a HPLC method was developed to determine the number of products in each pot. All 24 pots were screened for inhibitory activity against the rat liver DHFR. Two pots showed good inhibitory activity and the products in them were individually synthesized, characterized and biologically tested again. One lead compound was identified amongst all the compounds synthesized, and would be further optimized.

Intrapulmonary and gastric teratoma : report of two cases

The lung and stomach are very unusual sites for teratoma. The histologic findings of intrapulmonary and gastric teratomas are not different from those arising in usual sites, such as the ovary or testis. However, preoperative diagnosis is sometimes difficult to make partly because of unusual location. We report here two cases of teratoma, one intrapulmonary teratoma and the other gastric. The intrapulmonary teratoma in our study had an endobronchial tumor growth, which rules out mediastinal teratoma. Meanwhile gastric teratomas usually present as a submucosal tumor and most cases are reported in infancy and childhood. Gastric teratoma in this study occurred in a 27-year-old man. To the best of our knowledge, this case of intrapulmonary teratoma is the eighth and the gastric teratoma is the first to be reported in Korea.

Acyl-CoA: cholesterol acyltransferase inhibitory activity of ginseng sapogenins, produced from the ginseng saponins

Ginseng sapogenins were produced from ginseng saponins, isolated from Korean ginseng roots. Ginseng saponins very mildly inhibited acyl-CoA:cholesterol acyltransferase (ACAT) in vitro, however, the sapogenins showed strong inhibitory activity on microsomal ACAT. Therefore, the sapogenins will be one of key ingredients of ginseng affected a lowering of the serum total cholesterol level.

Glucocorticoids prevent NF-kappaB activation by inhibiting the early release of platelet-activating factor in response to lipopolysaccharide

Lipopolysaccharide (LPS) is a known inducer of numerous pro-inflammatory events including the production of platelet-activating factor (PAF). PAF released in response to LPS is a major contributor to the pathological events associated with endotoxemia. The present study demonstrates that dexmethasone (DEX) inhibited the LPS-induced early plasma PAF raise in a dose- and time-dependent manner. In addition, DEX prevented the subsequent PAF-mediated pathological phenomena such as anaphylactic shock-like symptoms, symptoms of disseminated intravascular coagulation and hemorrhage in renal medullae. DEX or the PAF antagonist BN 50739 significantly inhibited LPS-induced NF-kappaB activation. The inhibition of NF-kappaB activation by DEX was overcome by the injection of exogenous PAF. Administration of PAF or LPS resulted in a rapid loss of IkappaBalpha protein. The LPS-induced degradation of IkappaBalpha was prevented by pretreatment with BN 50739, suggesting that PAF is a critical intermediate in the LPS-triggered degradation of IkappaBalpha protein. DEX prevented the LPS-induced IkappaBalpha degradation, which was also reversed by exogenous PAF. Administration of DEX or BN 50739 caused an increase in cytoplasmic IkappaBalpha level. Our results indicate that DEX inhibits IkappaBalpha degradation and subsequent NF-kappaB activation through blocking the initial release of PAF.

Distribution of carcinoembryonic antigen and biologic behavior in colorectal carcinoma

PURPOSE

Carcinoembryonic antigen is assumed from the results of several experiments to be associated with invasion of colorectal carcinoma by adhesion or contact inhibition. The patterns and the intensity of carcinoembryonic antigen distribution in colorectal carcinoma were assessed to verify whether they were correlated with malignant potential from those biologic characteristics.

METHODS

Carcinoembryonic antigen distribution was tested in the archival samples of 149 colorectal carcinomas by immunohistochemistry, using three characterized anti-carcinoembryonic antigen monoclonal antibodies: T84.66, PR1A3, and PR3B10. The distribution patterns in neoplastic tissue were categorized into unstained, apicoluminal, and diffuse cytoplasmic patterns. Tumor, invasive tumor margin, and tissue surrounding the tumor were examined.

RESULTS

Although all three antibodies revealed a positive correlation, T84.66 showed better discrimination than the others. Although none of the negative staining of the tumor or invasive tumor margin showed recurrence, the apicoluminal pattern showed recurrence, and the diffuse pattern showed the most frequent recurrence (P < 0.01). Recurrence was also associated with staining intensity in the apicoluminal pattern in both the tumor and invasive tumor margin (P < 0.05). Infiltrative tumor growth and lymph node metastasis were more frequent in cases of positive staining in tissue surrounding the tumor. Patients with the apicoluminal pattern achieved longer survival than patients with the diffuse-cytoplasmic pattern in the invasive tumor margin (P = 0.024) by a multivariate analysis including tumor stage and histologic differentiation.

CONCLUSION

The distribution of carcinoembryonic antigen in tumors and surrounding tissue seems to be closely correlated with invasiveness and metastatic behavior in colorectal carcinoma. Carcinoembryonic antigen immune staining can be considered as an efficient tool to determine groups with risk of recurrence.

Identification of a zeta-crystallin (quinone reductase)-like 1 gene (CRYZL1) mapped to human chromosome 21q22.1

To identify a new gene(s) located on the yeast artificial chromosome (YAC) clone D142H8 that was mapped to human chromosome 21q22.1, purified YAC DNA from the clone was utilized directly as a probe to screen a human brain cDNA library after the suppression of human repetitive DNA. One cDNA clone hybridizing specifically to the YAC D142H8 DNA was identified. The clone has an insert of 1341 bp and the longest open reading frame of 349 amino acids. A search of GenBank revealed that the clone has a high degree of homology to zeta-crystallin (quinone reductase) at the amino acid level, and its nucleotide sequence represents the expressed sequence from the 50-kb segment of the human chromosome 21q11.1. Thus a new gene was named CRYZL1 (zeta-crystalline-like 1). Genomic Southern blot with total human and yeast DNAs suggests that CRYZL1 might be a single-copy gene. The fluorescence in situ hybridization procedure was applied, and the results showed that the gene mapped to the human chromosome 21q22.1 subband. The CRYZL1 mRNA was expressed in heart, brain, skeletal muscle, kidney, pancreas, liver, and lungs but at different levels in different tissues.

Transluminal angioplasty for middle cerebral artery stenosis in patients with acute ischemic stroke

BACKGROUND AND PURPOSE

Precutaneous transluminal angioplasty (PTA) is currently performed to treat supraaortic atherosclerotic lesions. Our purpose was to evaluate the safety and efficacy of PTA for middle cerebral artery (MCA) stenosis in patients with acute ischemic stroke.

METHODS

We performed PTA with the use of a microballoon (2-2.5 mm in diameter and 10-13 mm in length) in 10 consecutive patients (mean age, 48 years) who met the following criteria: high-grade M1 stenosis (> 70%) and mild neurologic deficits (NIH stroke scale < 4) and/or recurrent transient ischemic attacks (TIAs) resistant to anticoagulation, or a large area of hypoperfusion in the MCA territory on brain perfusion SPECT scans. During follow-up, we administered antiplatelet agents and evaluated the status of restenosis by angiography (n = 2), brain perfusion SPECT (n = 4), and/or transcranial Doppler sonography (TCD) (n = 7).

RESULTS

Stenotic arteries were successfully dilated in nine of 10 patients. Angioplasty failed in one patient because the balloon could not pass through the tortuous cavernous internal carotid artery. None of the patients experienced either peri- or postangioplasty complications. Residual stenosis was less than 50%, and clinical improvement, including elimination of TIAs in four patients who had suffered resistant TIAs, was observed in all patients; improvement of the cerebral perfusion was also noted in two patients with a large hypoperfusion area in the MCA territory. The average follow-up period was 11 months (range, 2 to 36 months). None experienced recurrent stroke during the follow-up period. TCD revealed decreased flow velocity of the MCA after angioplasty in seven patients.

CONCLUSION

PTA of the proximal portion of the MCA seems to be a safe and effective therapeutic technique for the prevention of secondary ischemic stroke.

Mutation of p53 and K-ras, and loss of heterozygosity of APC in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is the second most common malignant tumor in liver; however, the carcinogenic mechanism of ICC is poorly understood. To analyze the molecular carcinogenesis of ICC, we examined the alterations of the p53, APC, and K-ras genes in 40 surgically resected ICC cases. The single-strand conformation polymorphism/sequencing revealed a p53 mutation in 12 cases (30%). An immunohistochemical overexpression of the p53 gene was detected in 10 cases (25%). The PCR/RFLP showed loss of heterozygosity of APC in 4 of 17 informative cases (23.5%). And the PCR/RFLP assay of K-ras codon 12 revealed the mutation in nine cases (22.5%). Twenty-one cases (52.5%) showed an alteration of at least one of the examined genes, and six (15%) carried an abnormality in more than two genes. The analysis of the clinicopathologic findings disclosed a significant relationship between the genetic alteration and gross type of the tumor: the p53 mutation was prominent in the ICC of mass-forming type, and K-ras mutation occurred more frequently in the ICC of periductal extension type (p < 0.05). These data suggest that each of the examined genes is involved in the development of ICC and that the p53 and K-ras mutation may play a role in the tumor growth pattern.

Glucocorticoids prevent NF-kappaB activation by inhibiting the early release of platelet-activating factor in response to lipopolysaccharide

Lipopolysaccharide (LPS) is a known inducer of numerous pro-inflammatory events including the production of platelet-activating factor (PAF). PAF released in response to LPS is a major contributor to the pathological events associated with endotoxemia. The present study demonstrates that dexmethasone (DEX) inhibited the LPS-induced early plasma PAF raise in a dose- and time-dependent manner. In addition, DEX prevented the subsequent PAF-mediated pathological phenomena such as anaphylactic shock-like symptoms, symptoms of disseminated intravascular coagulation and hemorrhage in renal medullae. DEX or the PAF antagonist BN 50739 significantly inhibited LPS-induced NF-kappaB activation. The inhibition of NF-kappaB activation by DEX was overcome by the injection of exogenous PAF. Administration of PAF or LPS resulted in a rapid loss of IkappaBalpha protein. The LPS-induced degradation of IkappaBalpha was prevented by pretreatment with BN 50739, suggesting that PAF is a critical intermediate in the LPS-triggered degradation of IkappaBalpha protein. DEX prevented the LPS-induced IkappaBalpha degradation, which was also reversed by exogenous PAF. Administration of DEX or BN 50739 caused an increase in cytoplasmic IkappaBalpha level. Our results indicate that DEX inhibits IkappaBalpha degradation and subsequent NF-kappaB activation through blocking the initial release of PAF.

Structure-activity relationships of lignans from Schisandra chinensis as platelet activating factor antagonists

We studied the structure-activity relationships of lignans from Schisandra chinensis and their derivatives as platelet activating factor (PAF) antagonists. Strong activity was shown in lignans without an ester group at C-6, a hydroxyl group at C-7 or a methylene dioxy moiety and with an R-biphenyl configuration. 6(7)-Dehydroschisandrol A, a derivative of schisandrol A, showed the highest activity (IC50, 2.1x10(-6) M) in this study.

Chemical modification of analytes in speciation analysis by capillary electrophoresis, liquid chromatography and gas chromatography

Chemical modification of target analytes is widely used in modern analytical methods. This review focuses on the application of chemical modification techniques is the simultaneous analysis of metallic species by capillary electrophoresis, liquid chromatography and gas chromatography. Emphasis is placed on the procedures relating to analyses carried out by capillary electrophoresis. The development of this topic in the past five years is evaluated for liquid chromatography and gas chromatography. The advantages, performance and application in real samples are compared for the three techniques.

Retinoic acids up-regulate steroidogenic acute regulatory protein gene

The steroidogenic acute regulatory (StAR) protein plays essential roles in the delivery of cytosolic cholesterol into the mitochondrial inner membrane, which is an acute regulated and rate-limiting step for the steroid hormone synthesis. Since retinoic acids (RAs) are known to induce the synthesis of steroid hormones in mouse Leydig cells in vitro, mouse Leydig tumour cells, K28, were used to determine the effect of RAs on the level of StAR mRNA by Northern blot analysis. The level of StAR mRNA reached the maximum in a 4-8 h treatment with all-trans-RA (atRA) or 9-cis-RA (9cRA), and the effects were dose-dependent. The effect of 9cRA on the levels of StAR mRNA was blocked by actinomycin D, which indicates that 9cRA might exert a direct effect on the transcription of the gene. Promoter/reporter constructs containing a 5'-flanking region of the mouse or rat StAR gene were prepared, and luciferase activity was assayed following transient transfection into K28 or adrenal tumour cells, Y1. The result revealed that the luciferase activity was increased by 4-5-fold in response to the treatment of 9cRA, which indicated that 9cRA participates transcriptional activation of the StAR protein gene.

Inhibitory constituents against HIV-1 protease from Agastache rugosa

Two diterpenoid compounds, agastanol (1) and agastaquinone (2), were isolated from the roots of Agastache rugosa (Labiatae). Compound 1 and 2 showed significant inhibitory effects against human immunodeficiency virus type 1 (HIV-1) protease activity with IC50 values of 360 and 87 microM, respectively.

Decreased immunoexpression of prostate inhibin peptide in prostatic carcinoma: a study with monoclonal antibody

Prostate inhibin peptide (PIP) is a follicle-stimulating hormone (FSH) regulating peptide produced by the prostate. The mechanism of its endocrine role in regulating prostate growth is believed to be androgen-independent but FSH-dependent. Previous studies using polyclonal antibody proposed PIP as a prostatic-specific marker in cancer diagnosis. However, the recently available monoclonal antibody has not yet been evaluated. Paraffin sections of 72 prostatectomy specimens for prostate cancer with or without hormonal blockage therapy and 10 nonneoplastic prostate tissues from autopsy were stained by using PIP monoclonal antibody (clone: 4A6A6) with the avidin-biotin complex method. PIP reactivity was semiquantitatively estimated in prostatic carcinoma (PCA), prostatic intraepithelial neoplasia (PIN), benign prostatic hyperplasia (BPH) and normal tissue in each case when ever present. Statistical analyses were performed accordingly. PIP expression is predominantly cytoplasmic. Urothelium, seminal vesicles, inflamed prostatic glands, basal cells, and squamous metaplasia were negative for PIP. Average percentage of cells expressing PIP was significantly decreased in PIN (40%) and PCA (14%) when compared with BPH (81%) and normal tissue (68%). There was no correlation of tumor PIP level with patient's age, tumor size, Gleason score, tumor stage, or the usage of preoperative hormonal blockage therapy. PIP monoclonal antibody should be used with caution as a prostate-specific marker in surgical pathology. The mechanism for this alteration and the effect of PIP on prostatic tumor growth, particularly in patients under a variety of hormonal therapies, needs further study.

Location of the primary motor cortex in schizencephaly

BACKGROUND AND PURPOSE

Functional reorganization of the brain can result from congenital brain disorders as well as from brain infarction. The purpose of our study was to use functional MR imaging to determine whether reorganization of brain function occurs in patients with schizencephaly.

METHODS

Four patients with schizencephaly (three right-handed, one ambidextrous) presented with seizures. Associated lesions included agenesis of the corpus callosum (n = 1) and absence of the septum pellucidum (n = 1). Functional MR imaging was performed in each patient using a single-section fast low-angle shot (FLASH) blood oxygen level-dependent (BOLD) technique at 1.5 T in a standard head coil. The motor cortex was initially identified on an axial T1-weighted anatomic image. Thirty consecutive images were obtained during a motor task consisting of repetitive finger-to-thumb opposition. The percentage of change in increased signal intensity was calculated for the primary motor area. An ipsilateral activation index was used to compare the affected with the unaffected hemisphere.

RESULTS

The percentage of change in increased signal intensity in the area of activation ranged from 4.8% +/- 0.9 to 9.2% +/- 1.2 (mean, 5.6% +/- 1.5). The ipsilateral activation index in the affected hemisphere was 0.00 to 0.38, whereas that in the unaffected hemisphere was 15.4 to infinity. The difference in the ipsilateral activation index between each hemisphere was considered significant.

CONCLUSION

Our results showed increased activation in the unaffected hemisphere in patients with schizencephaly, which may reflect functional reorganization of the motor area in patients with this congenital disorder.

Chiral resolution of atropine, homatropine and eight synthetic tropinyl and piperidinyl esters by capillary zone electrophoresis with cyclodextrin additives

Chiral resolution of atropine, homatropine and eight synthetic tropinyl and piperidinyl esters were studied by capillary zone electrophoresis with cyclodextrin additives. Atropine and eight synthetic derivatives were successfully resolved by heptakis-(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD) at concentrations ranging from 10 to 40 mM. Homatropine was baseline resolved by 10 mM beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin (HP-beta-CD), respectively. The developed method was employed for the determination of atropine enantiomers in human serum.

Clinicopathologic characteristics of replication error-positive gastric carcinoma

Microsatellite instability (MI), an expansion or contraction of microsatellites, is a manifestation of replication errors (RERs) that is recognized as performing an important role in carcinogenesis in a proportion of gastric carcinomas. We analyzed 96 cases of sporadic gastric carcinomas for the occurrence of MI in BAT-26 and other six microsatellite loci. Gastric carcinomas with BAT-26 alteration demonstrated a higher proportion of unstable loci in other examined microsatellites than did gastric carcinomas without BAT-26 alteration. We classified gastric carcinomas with BAT-26 alteration as RER+ and compared the RER status with their clinicopathologic features. Ten (10.4%) of 96 gastric carcinomas showed RERs: 2 (7.7%) of 26 early gastric carcinomas and 8 (11.4%) of 70 advanced gastric carcinomas were RER+. RER+ gastric carcinomas were significantly associated with older age, elevated gross type (Borrmann Type 2 or EGC IIa), expanding growth pattern (Ming's classification), and minimal desmoplasia. Although statistically not significant, RER+ gastric carcinomas showed more frequent intestinal type (Lauren's classification), more antral involvement, and lower lymph node metastasis than did RER- gastric carcinomas. There was no association between RER status and intratumoral lymphocyte infiltration or histologic differentiation. In conclusion, RER+ gastric carcinomas demonstrated distinct clinicopathologic features, and BAT-26 was a useful marker for assessing the RER status of gastric carcinomas.

Gating of single N-type calcium channels recorded from bullfrog sympathetic neurons

For many neurons, N-type calcium channels provide the primary pathway for calcium influx during an action potential. We investigated the gating properties of single N-type calcium channels using the cell-attached patch technique. With 100 mM Ba2+ in the pipet, mean N-channel open probability (Po, measured over 100 ms) increased with depolarization, but the range at a single voltage was large (e.g., Po at +40 mV ranged from 0.1 to 0.8). The open dwell time histograms were generally well fit by a single exponential with mean open time (tauo) increasing from 0.7 ms at +10 mV to 3.1 ms at +40 mV. Shut time histograms were well fit by two exponentials. The brief shut time component (taush1 = 0.3 ms) did not vary with the test potential, while the longer shut time component (taush2) decreased with voltage from 18.9 ms at +10 mV to 2.3 ms at +40 mV. Although N-channel Po during individual sweeps at +40 mV was often high ( approximately 0.8), mean Po was reduced by null sweeps, low Po gating, inactivation, and slow activation. The variability in mean Po across patches resulted from differences in the frequency these different gating processes were expressed by the channels. Runs analysis showed that null sweeps tended to be clustered in most patches, but that inactivating and slowly activating sweeps were generally distributed randomly. Low Po gating (Po = 0.2, tauo = 1 ms at +40 mV) could be sustained for approximately 1 min in some patches. The clustering of null sweeps and sweeps with low Po gating is consistent with the idea that they result from different modes of N-channel gating. While Po of the main N-channel gating state is high, the net Po is reduced to a maximum value of close to 0.5 by other gating processes.