Role of T cells in bronchoalveolar space in the development of interstitial pneumonia induced by superantigen in autoimmune-prone mice

To study the mechanisms underlying the development of interstitial pneumonia in autoimmune disease, we analyzed bronchoalveolar lavage fluid (BALF) in an animal model of interstitial pneumonia in which an intratracheal instillation of staphylococcal enterotoxin B (SEB) induced interstitial pneumonia in autoimmune-prone mice. Increases in the numbers of total cells, macrophages, lymphocytes, and neutrophils were observed in BALF from SEB-treated MRL +/+ mice, and peaked at 3 d after SEB administration (Day 3). Flow cytometric analyses revealed increases in SEB-reactive Vbeta8(+) T cells, indicating that SEB-reactive cells play an important role in bronchoalveolar space. The expressions of tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, JE/monocyte chemoattractant protein-1, regulated on activation, normal T cells expressed and secreted, and KC/gro messenger RNA (mRNA) in BALF cells from SEB-treated mice peaked at Day 3. Increased expression of TNF-alpha mRNA was observed mainly in macrophages and CD8(+) T cells, and the increase in IFN-gamma mRNA was observed mainly in CD8(+) T cells in BALF at Day 3. The expression of platelet-derived growth factor mRNA was very weak at Day 3 but strongly expressed at Day 14. An immunosuppressant, FK506, but not corticosteroid, suppressed SEB-induced T-cell expansion in BALF as well as increased cytokine and chemokine production in the bronchoalveolar space of SEB-treated mice. Histologically, FK506 but not corticosteroid significantly reduced both the cell infiltration to alveolar septal walls and the synthesis of pulmonary collagen fibers. Further, transfer of T cells of MRL +/+ mice with SEB into SCID mice gave rise to interstitial pneumonia. These results suggest that superantigen-reactive T cells in the bronchoalveolar space may trigger the development of interstitial pneumonia in this model.

Identification of the second tonicity-responsive enhancer for the betaine transporter (BGT1) gene

When certain cells are exposed to a hypertonic solution, transcription of the BGT1 gene is markedly increased. The ensuing rise in betaine transport leads to cellular accumulation of betaine that protects the cells from the stress of hypertonicity. We have previously identified a tonicity-responsive enhancer (TonE1) in the 5' flanking region of the BGT1 gene. It was recognized, however, that full activation of transcription requires additional sequence upstream from the TonE1. Now we report that there is another TonE (named TonE2) 72 base pairs upstream from the TonE1. TonE1 and TonE2 act synergistically to stimulate transcription of BGT1 in response to hypertonicity.

Detection of anti-LKM-1(anti-CYP2D6) by an enzyme-linked immunosorbent assay in adult patients with chronic liver diseases

Anti-liver kidney microsome-1 (LKM-1) autoantibody, which is a serological marker for autoimmune hepatitis type II, recognizes Cytochrome P450 IID6 (CYP2D6). This autoantibody is also detected in a portion of patients with chronic hepatitis C. Anti-LKM-1 has been measured by indirect immunofluorescence (IF) using rat liver and kidney sections. However, this method has some problems in specificity and is so laborious to handle with many samples. In this study, in order to determine anti-LKM-1, we established an enzyme-linked immunosorbent assay (ELISA) for anti-CYP2D6 using a recombinant CYP2D6 fusion protein. We studied sera from 29 patients positive for anti-LKM-1 by the new ELISA. We further studied sera from a total of 301 patients with various liver diseases and 100 sera from normal controls negative for anti-LKM-1 by the new ELISA. The specificity of the ELISA was ascertained by absorption tests using sera positive for anti-LKM-1. In 29 sera from patients positive for anti-LKM-1 by IF, we found a good correlation between the logarithms of the antibody titers determined by IF and ELISA indexes obtained by our new method. Anti-CYP2D6 was positive in 12 of 12 (100%) patient with autoimmune hepatitis type II and 16 of 17(94.1%) with chronic hepatitis C positive for anti-LKM-1 by IF. In other 401 sera negative for anti-LKM-1 by IF, anti-CYP2D6 was all negative except a few sera. We established a new ELISA for anti-LKM-1 (anti-CYP2D6). This ELISA system is sensitive, antigen-specific and easy to be done. Therefore, this assay allows a routine test of many serum samples, especially for diagnosing autoimmune hepatitis type II.

Detection of anti-branched chain 2-oxo acid dehydrogenase complex (BCOADC)-E2 antibody in primary biliary cirrhosis by ELISA using recombinant fusion protein

Anti-M2 of anti-mitochondrial antibody (AMA) is a serological marker of primary biliary cirrhosis (PBC). Anti-pyruvate dehydrogenase complex-E2 (anti-PDC-E2) is recognized as the most frequently occurring anti-M2, and a routine laboratory test for this antibody has already been established. However, it is also known that there are patients with PBC who are negative for anti-PDC-E2. For the serological diagnosis of these patients, immunoblotting for anti-M2s is indicated. However, the technique currently utilized is too laborious to allow testing of a large number of samples. In this study, we have developed an enzyme-linked immunosorbent assay (ELISA) using a recombinant fusion protein in order to evaluate anti-branched chain 2-oxo-acid dehydrogenase complex-E2 (anti-BCOADC-E2), another frequently occurring anti-M2 in PBC patients. KB cell lines (CCL 17) were utilized as source material, and BCOADC-E2 cDNA (971 bp) including the lipoic acid binding domain was amplified by polymerase chain reaction. The amplified region was subcloned into pEX-3 vectors and expressed, and the resulting fusion protein (beta-galactosidase/BCOADC-E2) was utilized as antigen for an ELISA. We ascertained the specificity of this antigen by inhibition tests with ELISA and immunoblotting. We defined the cut-off optical density (OD) value as the mean + 3 SD (0.146) of sera from 60 normal controls. Anti-BCOADC-E2 could not be detected with this assay in sera from normal controls and from patients with autoimmune hepatitis and chronic viral hepatitis. Anti-BCOADC-E2 was detected in 119 of 210 sera (56.7%) from patients with PBC. In addition, anti-BCOADC-E2 was detected in 48 of 99 (48.5%) sera from PBC patients who were negative for anti-PDC-E2. Here, we have succeeded in developing a new ELISA for detecting anti-BCOADC-E2. This system is antigen-specific and easily performed. This assay should allow routine testing of a large number of serum samples, and should become especially useful for the serodiagnosis of anti-PDC-E2-negative PBC patients.

Elevated bronchoalveolar concentrations of MCP-1 in patients with pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) is a rare disease of unknown aetiology characterized by accumulations of lipoproteinaceous material within the alveoli. The alveolar macrophages become increasingly foamy, and are thought to have a role in the pathogenesis of PAP. However, the mechanisms of macrophage recruitment are unclear. In the bronchoalveolar lavage fluid (BALF) of four patients with PAP and 20 normal control subjects, the following were examined: the monocyte chemotactic activity due to the chemokine monocyte chemoattractant protein (MCP)-1 with the use of a chemotactic chamber assay, the levels of MCP-1 by enzyme-linked immunosorbent assay, and the MCP-1 expression on lavage cells by immunocytochemistry and in situ hybridization. The monocyte chemotactic activity in the BALF of the PAP patients was markedly elevated, and the activity was completely absorbed by treatment with anti-MCP-1. The MCP-1 levels in the BALF were surprisingly high in the PAP group (25,100+/-472 pg x mL(-1)), whereas low levels of MCP-1 were detected in the normal control subjects (mean: never smokers 4.8; smokers 10.4 pg x mL(-1)). MCP-1 protein and messenger ribonucleic acid were expressed by macrophages from the PAP patients, and the expression was reduced according to foaming of the cells; there were monocyte-like macrophages with strong expression, small foamy cells with moderate expression, large foamy cells with a faint expression of MCP-1, and ghost cells with no expression. However, the increase of macrophage number in the PAP BALF was relatively small. These data suggest that monocyte chemoattractant protein(-1) expression by alveolar macrophages represents an amplification mechanism for the recruitment of additional macrophages to the alveoli in pulmonary alveolar proteinosis. It is possible that an ingestion of an excess of alveolar materials in pulmonary alveolar proteinosis may impair the macrophage function and the survival, resulting in the lack of a prominent increase in the macrophage number in bronchoalveolar lavage fluid.

Optical detection of synaptically induced glutamate transport in hippocampal slices

Although it has long been believed that glial cells play a major role in transmitter uptake at synapses in the CNS, the relative contribution of glial and neuronal cells to reuptake of synaptically released glutamate has been unclear. Recent identification of the diverse glutamate transporter subtypes provides an opportunity to examine this issue. To monitor glutamate transporter activity, we optically detected synaptically induced changes of membrane potential from hippocampal CA1 field in slice preparations using a voltage-sensitive dye, RH155. In the presence of ionotropic glutamate-receptor blockers, synaptic inputs gave rise to a slow depolarizing response (SDR) in the dendritic field. The amplitude of SDR correlated well with presynaptic activities, suggesting that it was related to transmitter release. The SDR was found to be caused by the activities of glutamate transporters because it was not affected by blockers for GABAA, nACh, 5-HT3, P2X, or metabotropic glutamate receptors but was greatly reduced by dihydrokainate (DHK), a specific blocker for GLT-1 transporter, and by D, L-threo-beta-hydroxyaspartate (THA), a blocker for EAAC, GLAST, and GLT-1 transporters. When SDR was detected with RH482 dye, which stains both glial and neuronal cells, 1 mM DHK and 1 mM THA were equally effective in suppressing SDR. The SDR was very small in GLT-1 knockout mice but was maintained in gerbil hippocampi in which postsynaptic neurons were absent because of ischemia. Because GLT-1 transporters are exclusively expressed in astrocytes, our results provide direct evidence that astrocytes play the dominant role in sequestering synaptically released glutamate.

Tonicity-responsive enhancer binding protein, a rel-like protein that stimulates transcription in response to hypertonicity

Hypertonicity (most often present as high salinity) is stressful to the cells of virtually all organisms. Cells survive in a hypertonic environment by increasing the transcription of genes whose products catalyze cellular accumulation of compatible osmolytes. In mammals, the kidney medulla is normally hypertonic because of the urinary concentrating mechanism. Cellular accumulation of compatible osmolytes in the renal medulla is catalyzed by the sodium/myo-inositol cotransporter (SMIT), the sodium/chloride/betaine cotransporter, and aldose reductase (synthesis of sorbitol). The importance of compatible osmolytes is underscored by the necrotic injury of the renal medulla and subsequent renal failure that results from the inhibition of SMIT in vivo by administration of a specific inhibitor. Tonicity-responsive enhancers (TonE) play a key role in hypertonicity-induced transcriptional stimulation of SMIT, sodium/chloride/betaine cotransporter, and aldose reductase. We report the cDNA cloning of human TonE binding protein (TonEBP), a transcription factor that stimulates transcription through its binding to TonE sequences via a Rel-like DNA binding domain. Western blot and immunohistochemical analyses of cells cultured in hypertonic medium reveal that exposure to hypertonicity elicits slow activation of TonEBP, which is the result of an increase in TonEBP amount and translocation to the nucleus.

Effects of glucocorticoids and cyclosporine on IL-2 and I kappa B alpha mRNA expression in human peripheral blood mononuclear cells

To evaluate molecular mechanisms that might account for the heterogeneity in the in vitro responsiveness of individual subjects' peripheral blood mononuclear cells (PBMC) to immunosuppressive drugs, the authors quantitated in normal human cells the suppressive effects of the glucocorticoids prednisolone and methylprednisolone and of cyclosporine on interleukin-2 (IL-2) mRNA expression and IL-2 production, as well as the stimulatory effect of these drugs on IkappaBalpha mRNA expression. As expected, cyclosporine was significantly more suppressive than either glucocorticoid of IL-2 mRNA expression and IL-2 production by mitogen-stimulated PBMC, with variable degrees of inhibition in cells from individual subjects. The authors confirmed in human PBMC the stimulation of IkappaBalphamRNA expression by the glucocorticoid reported by others in HeLa and transfected Jurkat cell lines. In addition, the authors observed a stimulatory effect on IkappaBalpha mRNA expression by cyclosporine as well in 8 of 10 PBMC preparations studied, suggesting a possible role of calcineurin in the regulation of IkappaBalpha production. Interindividual variability in the intracellular mechanisms of action, possibly based on molecular polymorphisms, might be one factor contributing to differences among patients in their clinical responses to treatment with such drugs.

Activation of dihydropyridine sensitive Ca2+ channels in rat hippocampal neurons in culture by parathyroid hormone

We examined the effects of parathyroid hormone (PTH) on rat hippocampal neurons in culture to determine whether it caused a similar intracellular calcium concentration ([Ca2+]i) increase in these cells to that seen with renal epithelial cells and found that PTH induced the effect in about 30% of the neurons. The effects appeared gradually during continuous administration of full-length PTH(1-84) or its active fragment, PTH(1-34), but not of an inactive fragment, PTH(39-84). However, the active fragment of the PTH-related peptide (PTHrP(1-34)) had little effect on [Ca2+]i during 60 min of administration. The PTH effect was inhibited by nifedipine, an L-type Ca2+ channel antagonist, and facilitated by S-(-)-BAY K 8644, an L-type Ca2+ channel agonist. Our findings suggest that PTH is one of the causal factors for the age-related increase in the density of voltage gated Ca2+ channels in hippocampal neurons.

Differences in antigenic sites, recognized by anti-liver-kidney microsome-1 (LKM-1) autoantibody, between HCV-positive and HCV-negative sera in Japanese patients

Anti-liver-kidney microsome-1 (LKM-1), which reacts with cytochrome P450 IID6 (CYP2D6), is an autoantibody present in autoimmune hepatitis type II, which affects primarily young patients. Recently, it has been shown some adult patients with chronic hepatitis C are also positive for anti-LKM-1. Thus, anti-LKM-1-positive patients can be classified into two subgroups: (1) those with autoimmune hepatitis type II and (2) those with chronic hepatitis C. We investigated the antigenic epitopes of CYP2D6 with which each of these two anti-LKM-1-positive subgroups reacted. Multiple deletion mutants of CYP2D6 were constructed from a human liver cDNA library and five recombinant fusion proteins expressed. Antigenic epitopes were determined by immunoblot analysis using these proteins. Anti-LKM-1 present in HCV-negative sera recognized at least two peptide regions of aa213-280 and aa341-477 of human CYP2D6. In contrast, anti-LKM-1 present in HCV-positive sera recognized only a single region of aa341-477. Thus, the sera of patients with autoimmune hepatitis type II and patients with chronic hepatitis C recognize different antigenic epitopes of the CYP2D6 molecule. To our knowledge, this is the first time LKM-1 autoantigens have been analyzed at the molecular level in Japanese patients.

Differential roles of two types of voltage-gated Ca2+ channels in the dendrites of rat cerebellar Purkinje neurons

The distribution and function of voltage-gated Ca2+ channels in Purkinje neurons in rat cerebellar slices were studied using simultaneous Ca2+ imaging and whole-cell patch clamp recording techniques. Voltage-gated Ca2+ channels were activated by applying depolarizing voltage steps through the pipette attached at the soma in a voltage-clamp mode in the presence of tetrodotoxin. Poor space clamp due to extensive arborization of the dendrites allowed the dendrites to fire Ca2+ spikes. Ca2+ imaging with Fura-2 injected through the pipette, showed a steady [Ca2+]i increase at the soma and transient, spike-linked [Ca2+]i jumps in the dendrites. omega-Agatoxin-IVA (200 nM) abolished the depolarization-induced Ca2+ spikes, the spike-linked [Ca2+]i increase in the dendrites, and the steady [Ca2+]i increase at the soma. omega-Conotoxin-GVIA (5 microM) and nifedipine (3 microM) had no significant effect on the depolarization-induced responses. In the presence of 4-aminopyridine(2 mM) and omega-Agatoxin-IVA, transient [Ca2+]i increases remained in the dendrites. Low concentrations of Ni2+(100 microM) reversibly suppressed this [Ca2+]i increase. The voltage for half-maximal activation and inactivation of this component were lower than -50 mV and -31 mV, respectively. In normal conditions, low concentration of Ni2+ slowed the onset of the Ca2+ spike without changing the time course of the spikes or the amplitude of the accompanying [Ca2+]i increase. These results show that omega-Agatoxin-IVA-sensitive Ca2+ channels are distributed both in the soma and the dendrites, and are responsible for dendritic Ca2+ spikes, whereas low-voltage activated, Ni2+-sensitive Ca2+ channels are distributed in the whole dendrites including both thick and fine branches, and provide boosting current for spike generation.

Cis- and trans-acting factors regulating transcription of the BGT1 gene in response to hypertonicity

We have previously identified a tonicity-responsive enhancer (TonE) in the promoter region of the canine BGT1 gene. TonE mediates hypertonicity-induced stimulation of transcription. Here, we characterize TonE and TonE binding proteins (TonEBPs) to provide a biochemical basis for cloning of the TonEBPs. Mutational analysis applied to both hypertonicity-induced stimulation of transcription and TonEBP binding reveals that TonE is 11 base pairs in length, with the consensus sequence of (C/T)GGAAnnn(C/T)n(C/T). Activity of the TonEBPs increases in response to hypertonicity with a time course similar to that of transcription of the BGT1 gene. Studies with inhibitors indicate that translation, but not transcription, is required for activation of the TonEBPs. Phosphorylation is required for the stimulation of transcription but not for activation of DNA binding by the TonEBPs. In vivo methylation by dimethyl sulfate reveals that the TonE site of the BGT1 gene is protected with a time course like that of activity of the TonEBPs and activation of transcription. Ultraviolet cross-linking indicates that the TonEBPs share a DNA binding subunit of 200 kDa.

A novel antibody directed against a three-dimensional configuration of a 95-kDa protein in patients with autoimmune hepatic diseases

Sera from patients with primary biliary cirrhosis recognize various cellular components, such as mitochondria, centromere, nuclear envelope, and multiple nuclear dot antigens. There also appears to be a novel antibody reacting with a particular protein in these sera. The presence of this antibody was investigated by double immunodiffusion using rat liver cytoplasmic antigens, by immunoprecipitation of [35S]-methionine labelled HeLa cell extracts, and by immunoblot using disrupted HeLa cell extracts. Test sera were obtained from 491 patients with various liver diseases. Nine of the 491 sera were found to react with a 95-kDa protein as determined by immunoprecipitation of [35S]-methionine labelled HeLa cell extracts and by double immunodiffusion using a rat liver microsomal preparation. However, these same nine sera showed no reaction in the immunoblot assay. On the basis of its molecular mass and its presence in the cytoplasmic fraction, this antigen was named p95 C. This anti-p95 C antibody was detected in six of 50 (12%) sera from patients with primary biliary cirrhosis, and in three of 31 (9.7%) sera from patients with autoimmune hepatitis, but not in any of the remaining 410 sera obtained from patients with other hepatic diseases. It is concluded that anti-p95 C antibody reacts primarily with the native form of the 95-kDa protein, and represents another possible analyte for diagnosing autoimmune liver diseases.

Chronic hepatitis C associated with anti-liver/kidney microsome-1 antibody is not a subgroup of autoimmune hepatitis

To determine whether "autoimmune hepatitis type IIb" should be categorized as a subgroup of autoimmune hepatitis, we conducted a clinicopathological study of 25 adult Japanese patients who were positive for anti-liver/kidney microsome-1 (anti-LKM-1) anti-body and infected with the hepatitis C virus (HCV). Anti-LKM-1 was determined by indirect immunofluorescence and by the double immunodiffusion assays we have developed. Twenty-two patients did not present any unusual symptoms or any associated diseases during the course of their chronic HCV infection. The spectrum of HCV genotypes of these patients did not significantly differ from that of anti-LKM-1-negative Japanese patients with chronic hepatitis C. Histological examination of liver biopsy specimens showed the usual characteristics of chronic hepatitis C and lack of characteristics of autoimmune hepatitis type I. No disease-specific HLA haplotypes were noted, and HLA-DR4, which is detectable in 88.7% of Japanese patients with autoimmune hepatitis type I, was detected in only 50.0% of our group, the same rate as the background frequency. Prednisolone was effective in none of the six patients treated, but interferon was effective in six of ten treated patients (60%). From these results, we conclude that "autoimmune hepatitis type IIb" should not be categorized as autoimmune hepatitis, and that this subgroup is essentially chronic hepatitis C in which an autoantibody has been produced during the course of chronic HCV infection.

[Western blot analysis of anti-M2 antibodies in anti-mitochondrial antibody-negative primary biliary cirrhosis]

One variety of anti-mitochondrial antibody(AMA) is characteristically found in sera from patients with primary biliary cirrhosis(PBC). The major target antigens of this type of AMA are M2s. It is well known, however, that AMA-negative PBC also exists. An alternative disease concept, called autoimmune cholangiopathy, recently has been advocated. This new concept is defined by the following criteria: 1)the failure to detect AMA and anti-M2, 2)the detection of a diffuse type of anti-nuclear antibody and anti-smooth muscle antibody, 3)pathological findings compatible with PBC, and 4)the effectiveness of prednisolone. However, the difference between AMA-negative PBC and autoimmune cholangiopathy is controversial. Therefore, we analyzed antibodies to four major M2 proteins with Western blotting in 34 cases of immunofluorescent AMA-negative PBC. In 31(91.2%) of these 34 AMA-negative sera, antibodies to at least one of these four major M2 proteins was detected. In serum samples from 34 control patients with AMA-positive PBC, antibodies to at least one of these four proteins were detected in all cases. In addition, we studied the frequency of cases which satisfied the serological criteria of autoimmune cholangiopathy. In only one(0.7%) of 141 cases was the serological criteria met. We conclude that to clarify the serological differences between autoimmune cholangiopathy and AMA-negative PBC, the analysis of M2 proteins by Western blotting is essential.

[Establishment of the optimal conditions for detecting anti-M2 by western blotting in primary biliary cirrhosis]

Anti-mitochondrial antibodies(AMA) are serodiagnostic markers for primary biliary cirrhosis(PBC) but heterogenous in antigen molecules which they recognize. A disease-specific AMA for PBC is anti-M2. The conventional examination methods are indirect immunofluorescence and ELISA. However, there are some problems in specificity, because the antigen preparations used are crude. Thus, analysis with Western-blotting(W-B) is needed, because it allows the identification of a molecule which the antibody reacts with. In this report, we established the optimal conditions for detecting anti-M2 with W-B in PBC. As antigen, we used mitochondrial fractions derived from beef hearts. Because a positive band at 74 kDa became negative after absorbing sera with PDH purified from porcine hearts, this band corresponded to major antigeneity of anti-M2. Titration experiments with SDS-PAGE showed that the optimal concentration of this antigen preparation for loading is 0.04 mg/ml. We also performed titration experiments to determine the optimal dilutions for second antibodies and serum samples. The results showed that the optimal dilution for second antibodies, anti-IgG and anti-IgM, were 1:3000 and 1:1000, respectively. The optimal dilution for serum samples was shown to be 1:10(2). Moreover, the W-B technique gave a positive result even for sera from AMA-negative PBC patients which had tested negative with conventional methods, if undiluted sera were examined or if anti-IgG or anti-IgM was used as a second antibody. Thus, the W-B technique is more sensitive than conventional methods of analysis. Based on these results, we will be able to detect anti-M2 with maximum efficiency, thus improving our ability to study the relationship between anti-M2 and the pathological conditions in PBC.

Properties of calcium spikes revealed during GABAA receptor antagonism in hippocampal CA1 neurons from guinea pigs

Properties of calcium spikes revealed during GABAA receptor antagonism in hippocampal CA1 neurons from guinea pigs. J. Neurophysiol. 78: 2269-2279, 1997. Intracellular electrical responses and changes in intracellular calcium concentration ([Ca2+]i) in response to activation of synaptic inputs and to DC injections were recorded simultaneously from CA1 pyramidal neurons (n = 42) in guinea pig hippocampal slices. In the presence of the gamma-aminobutyric acid-A (GABAA) receptor antagonists, bicuculline (mu M) and picrotoxin (10 mu M, broad (>20 ms) all-or-none spikes were induced by activation of synaptic inputs (20 pulses, 30 Hz) and were accompanied by a simultaneous rapid and large rise in [Ca2+]i (34 of 34 cells). By contrast, direct depolarizing current (0.7 nA, 1 s) induced spikes having short duration, during which time the spike firing pattern was observed not to be significantly affected. When Na+ channels were blocked by QX-314 applied intracellularly through the recording microelectrode in the presence of GABAA receptor antagonists, broad spikes were frequently generated by activation of synaptic inputs (32 of 33 cells). These broad spikes were blocked by Cd2+ (200 mu M) or in Ca2+-free medium (6 of 6 cells) but were resistant to either tetrodotoxin (TTX; 1 micro M; 6 of 6 cells) or QX-314, whereas short-duration spikes were blocked by both TTX and QX-314. Based on these findings we conclude that broad and short-duration spikes are Ca2+ and Na+ spikes, respectively. To investigate the properties of the Ca2+ spikes, antagonists of a voltage-operated Ca2+ channel were applied to the evoked responses. Nifedipine (30 mu M), a L-type Ca2+ channel blocker, suppressed the generation of Ca2+ spikes, whereas Ni2+ (100 mu M), the T- and R-type Ca2+ channel blocker, and omega-agatoxin-IVA (omega-Aga-IVA, 60 nM), a P-type Ca2+ channel blocker, had little effect on the generation of Ca2+ spikes. Nifedipine suppressed the rise in [Ca2+]i induced by synaptic inputs up to 26% of the control in the soma and 18-32% in the dendrites (n = 5), respectively, whereas Ni2+ suppressed the rise by 12-27% (n = 5) in both soma and dendrites. omega-Aga-IVA showed little effect (less than a 10% change; n = 7). These results suggest that the GABAA inhibitory system tonically suppresses dendritic Ca2+ spikes, and the L-type Ca2+ channel plays a major role in the generation of Ca2+ spikes and in Ca2+ influx.