[TNM classification of ophthalmic malignant tumors]

The present TNM classification of ophthalmic malignant tumors (lid cancer, malignant melanoma of the lid, conjunctival cancer, conjunctival malignant melanoma, uveal malignant melanoma, retinoblastoma, orbital sarcoma and lacrimal gland cancer) has been explained according to the UICC in a book edited by M. H. Harmer and J. A. Oosterhuis. Five studies concerning the difference in clinical results with and without a treatment were shown to confirm the meaning and importance of TNM classification of ophthalmic malignancies.

Color-coded Doppler imaging of subclavian steal syndrome

We examined the usefulness of color-coded Doppler echography for evaluating hemodynamics in patients with subclavian steal syndrome. Eighteen patients with subclavian steal syndrome, aged 54 to 77 years, were investigated. The diagnosis was confirmed by conventional angiography and pulsed-wave Doppler sonography. Using color-coded Doppler echography, the common, internal and external carotid and vertebral arteries and the subclavian artery on the affected side were visualized. In all patients, color-coded images of the antegrade common carotid arterial flow and the retrograde vertebral arterial flow on the affected side were obtained. Rapid flow through stenotic lesions and reflux from vertebral to subclavian arteries at the vertebral arterial ostia were observed. Color-coded Doppler echography is superior to duplex echography without the color-coded mode, because the flow through the affected vertebral and subclavian arteries can be easily traced in detail and the images are persuasive. This method is beneficial for diagnosing subclavian steal syndrome.

Anti-streptococcal activity of homologous polymorphonuclear neutrophils from patients with surgically treated oral infections

The phagocytic bactericidal activity of homologous polymorphonuclear neutrophils (PMN), obtained from patients with severe, moderate and mild oral infections with Streptococci, was investigated. The drop in viable bacterial cell counts in PMNs from 3 patients with a severe infection, after 4 hours of incubation, was much greater than in PMNs from moderate or mild infections. We conclude that the phagocytic bactericidal activity of PMNs is stronger in patients suffering from severe oral infections with Streptococci.

Two types of calcium currents of the mouse bipolar cells recorded in the retinal slice preparation

In the vertebrate retina, the bipolar cell makes reciprocal synapses with amacrine cells at the axon terminal. It has been postulated that amacrine cells may control the transmitter release from bipolar cells by modulating their calcium currents (ICa). To clarify this possibility calcium currents were studied in bipolar cells of the mouse retina using a slice preparation. ICa was identified by voltage clamp protocols, ionic substitution and pharmacological tools. Depolarization to -30 mV from a holding voltage of -80 mV induced an inward current consisting of an initial transient and a long-lasting sustained component. The transient component was inactivated by holding the membrane at more positive voltages. Addition of 100 microM nifedipine suppressed the sustained component, leaving the transient component almost intact. The sustained component was enhanced when external solution contained 0.1 microM Bay K 8644 or when the external Ca2+ was substituted by equimolar Ba2+. Omega-conotoxin (10 microM omega-ctxn GVIA) did not alter either component. We concluded that the transient component is a low-voltage activated T-type ICa, while the sustained component is a high-voltage activated L-type ICa. T-type ICa was recorded in all cells tested, while L-type ICa was found only in cells that retained axon terminals ramifying in the inner plexiform layer. Thus, it is highly likely that L-type ICa is generated at the axon terminal and contributes to the transmitter release from the bipolar cell. The present results confirm that in addition to the T-type ICa that had been previously described, bipolar cells of the mammalian retina also contain L-type ICa similar to the one that has been reported in bipolar cells of the goldfish. The use of retinal slice preparation allowed us to record this current that was not seen previously in the dissociated mouse bipolar cells.

Appearance of a fast inactivating voltage-dependent K+ currents in developing cerebellar granule cells in vitro

To elucidate the molecular mechanisms that regulate the maturation of action potential, we began by examining voltage-dependent K+ currents, known to contribute to the maturation of action potential, of developing granule cells in mouse cerebellar microexplant cultures. The migration of developing granule cells in this culture is reported to mimic the in vivo process, but their specific identification is still incomplete. In this study, we identified and characterized granule cells in this culture. Immunocytochemical analysis found that granule cells migrated radially out from explants and subsequently formed small clusters and also that their morphology changed from a bipolar to a T shape during migration. Moreover, in the electrophysiological study, the GABA response of granule cells in this culture clarified that the electrophysiological properties of granule cells were normally maintained. We therefore have concluded, that this culture system is a powerful tool for investigating the differentiation of cerebellar granule cells. Based on these findings, we recorded voltage-dependent K+ currents of developing granule cells in this culture, while concurrently observing their morphology. Our results show that voltage-dependent K+ currents of developing granule cells change from delayed rectifier to A current in parallel with their morphological changes from bipolar to T-shaped cells.

Modulation of GABAC response by Ca2+ and other divalent cations in horizontal cells of the catfish retina

GABAC responses were recorded in cultured cone-driven horizontal cells from the catfish retina using the patch clamp technique. At a holding potential of -49 mV, a bicuculline-resistant inward current (IGABA) was observed when 10 microM GABA was applied. The amplitude of IGABA increased as the extracellular Ca2+ ([Ca2+]o) was increased. Concentration-response curves of IGABA at 2.5 and 10 mM -Ca2+-o had similar EC50 (3.0 and 3.1 microM) and Hill coefficients (1.54 and 1. 24). However, the maximal response estimated at 10 mM [Ca2+]o was larger than the maximal response at 2.5 mM [Ca2+]o. Increasing Ca influx through voltage-gated Ca channels and the resulting rise in the intracellular Ca2+ concentration had no effects on IGABA. However, IGABA was inhibited by extracellular divalent cations, with the following order of the inhibitory potency: Zn2+ > Ni2+ > Cd2+ > Co2+. The inhibitory action of Zn2+ on the [Ca2+]o-dependent IGABA increase was noncompetitive. The action of [Ca2+]o on IGABA was mimicked by Ba2+ or Sr2+. These results demonstrate that the extracellular domain of GABAC receptors has two functionally distinct binding sites represented by Ca2+ (facilitation) and Zn2+ (inhibition). Since [Ca2+]o and [Zn2+]o change into the opposite direction by light, it seems likely that they modify cooperatively the efficacy of the positive feedback consisting of the GABAC receptor.

Leptin stimulates the proliferation of murine myelocytic and primitive hematopoietic progenitor cells

Leptin, the product of obese gene, was originally identified as a factor regulating body-weight homeostasis and energy balance. The present study has shown that leptin acts on murine hematopoiesis in vitro. In the culture of bone marrow cells (BMC) of normal mice, leptin induced only granulocyte-macrophage (GM) colony formation in a dose-dependent manner, and no other types of colonies were detected even in the presence of erythropoietin (Epo). Leptin also induced GM colony formation from BMC of db/db mutant mice whose leptin receptors were incomplete, but the responsiveness was significantly reduced. The effect of leptin on GM colony formation from BMC of normal mice was also observed in serum-free culture, and comparable with that of GM-colony-stimulating factor (CSF ). Although leptin alone supported few colonies from BMC of 5-fluorouracil (5-FU)-treated mice in serum-free culture, remarkable synergism between leptin and stem cell factor (SCF ) was obtained in the colony formation. The addition of leptin to SCF enhanced the SCF-dependent GM colony formation and induced the generation of a number of multilineage colonies in the presence of Epo. When lineage (Lin)-Sca-1(+) cells sorted from BMC of 5-FU-treated mice were incubated in serum-free culture, leptin synergized with SCF in the formation of blast cell colonies, which efficiently produced secondary colonies including a large proportion of multilineage colonies in the replating experiment. In serum-free cultures of clone-sorted Lin-c-Kit+Sca-1(+) and Lin-c-Kit+Sca-1(-) cells, although synergism of leptin and SCF was observed in the colony formation from both cells, leptin alone induced the colony formation from Lin-c-Kit+Sca-1(-), but not Lin-c-Kit+Sca-1(+) cells. These results have shown that leptin stimulates the proliferation of murine myelocytic progenitor cells and synergizes with SCF in the proliferation of primitive hematopoietic progenitors in vitro.

Endoscopic follow-up study of development of gastric antral vascular ectasia associated with liver cirrhosis

Gastric antral vascular ectasia is an important cause of chronic gastrointestinal blood loss. However, its development and progression have not yet been clarified. We investigated its early lesions and progression by reviewing endoscopic films of five patients with gastric antral vascular ectasia followed for liver cirrhosis. In all patients, early findings were prepyloric red spots. In two patients, anemia due to gastrointestinal bleeding was already observed when vascular lesions were confined to the distal antrum. In the other three patients, anemia was observed 1-2 years after they showed a diagnostic pattern of gastric antral vascular ectasia. The vascular lesions gradually thickened and extended throughout the antrum, with the complete picture shown in 1.5-5 years. The pattern of distribution was classified into three types: diffuse spotty, diffuse confluent, and striped. These types could be predicted before the complete formation. Gastric antral vascular ectasia associated with liver cirrhosis started as prepyloric red spots and extended to the proximal antrum in various ways and varying time courses of less than 5 years; this entity may cause hemorrhage even in the early stage.

Ligand-dependent heterodimerization of thyroid hormone receptor and retinoid X receptor

The thyroid hormone receptors (TR) bind to cis-acting DNA elements as heterodimers with the retinoid X receptors (RXR). These heterodimers display distinct specificities in mediating the hormonal response to target gene transcription. We characterized the interaction between TRalpha1 and RXRalpha via their ligand binding domains (LBDs) and the effect of ligands on the interaction using a yeast two-hybrid system. The DNA binding domain (BD) of yeast Gal4 fusion to the LBD of TRalpha1 had no transcriptional activity on its own, but when it was coexpressed with the activation domain (AD) of yeast Gal4 fusion to LBD of RXRalpha conferred activation to a reporter gene harboring a Gal4 binding site, indicating that LBDs of TRalpha1 and RXRalpha interact with each other in solution. Furthermore, T3 and 9-cis-RA increased the reporter activity, and an additive effect was observed when both ligands were added, indicating that the TRalpha1.RXRalpha heterodimerization is augmented by their respective ligands in vivo. Using an in vitro pull-down experiment, we confirmed the ligand-dependent interaction observed in the yeast system. Matrix-bound glutathione S-transferase-RXRalpha specifically coprecipitated the 35S-labeled TRalpha1 above the control, and associated 35S-labeled TRalpha1 was increased by the addition of T3 and 9-cis-RA. These results imply a complex, sensitive cross-talk in vivo among nuclear receptors and their respective ligands through distinct hormonal signaling pathways.

Comparison of in vitro activity of azithromycin and ampicillin against 31 isolates of Streptococcus milleri

Antibacterial action of azithromycin against 31 strains of dental infection-derived Streptococcus milleri and tissue transfer of the agent were compared with ampicillin, the drug of first choice for dental infections. Concentrations required to inhibit 50% of isolates(MIC50) and Concentrations required to kill 50% of isolates(MBC50) were 0.10 and 0.2 microgram/ml, respectively, for azithromycin. The antibacterial action of azithromycin was 4 times more potent in than ampicillin. The MBC90 for azithromycin was 0.39 microgram/ml, for amplicill 3.13 micrograms/ml. Bactericidally, azithromycin was 8 times more active than ampicillin. The peak value of concentrations (Cmax) of azithromycin was 0.45 microgram/ml, about 1/10 that of ampicillin. The half-life of azithromycin was 10 hours, about 5 times longer than that of ampicillin. The contact time of MIC90 concentrations for azithromycin was 12 hours, distinctly longer than the 8 hours calculated for ampicillin. Azithromycin showed excellent tissue transfer concentrations: the gingival transfer concentration following oral administration of 500 mg/day ranged from 0.7-23.5 micrograms/ml.

Multiple hemorrhagic gastric ulcers due to polyarteritis nodosa

A 73-year-old man developed refractory multiple hemorrhagic gastric ulcers. Emergent gastrectomy was performed, and the diagnosis of polyarteritis nodosa was made by histologic evaluation of the resected stomach. Although gastric ulceration is a relatively rare complication of polyarteritis nodosa, it should be considered in the differential diagnosis of refractory hemorrhagic gastric ulcers. Emergent surgery may be indicated in such cases.

Quantitative analysis of Na+ and Ca2+ current contributions on spike initiation in the newt olfactory receptor cell

The contribution of Na+ (INa) and T-type Ca2+ (ICa,T) currents on the action potential initiation in newt olfactory receptor cells (ORC) was investigated quantitatively. Since both the Na+ channel and T-type Ca2+ channel show rapid inactivation, it was questioned how much INa and ICa,T are activated during the gradually depolarizing initial phase of the receptor potential. Because the conventional voltage clamp technique does not allow direct current measurement during voltage changes, we estimated the amplitude of INa and ICa,T in an ionic current model. The model was constructed based on voltage clamp experiments. The estimated ratio of ICa,T/INa during the action potential induced by ramp current injection was 0.59 +/- 0.03 (mean +/- SD) under control Ringer's solution. This ratio was more than twice as large as that (0.25) obtained from the previous voltage clamp experiment using step commands. This result suggests that the T-type Ca2+ channel carries a more significant amount of current to generate the action potentials than expected previously.

[Effects of globulin preparations on phagocytic killing of oral streptococci]

The phagocytic bacterial activity on Streptococcus intermedius and Streptococcus oralis, clinical isolates from patients suffering from severe oral surgical infections, was evaluated by using sera and neutrophils of patients who had been treated with polyethylene glycal treated human normal immunoglobulin (Venoglobulin-IH). The phagocytic function of the neutrophils against the two strains, approximately 10 cells/neutrophil, was unrelated to the administration of Venoglobulin-IH. The bactericidal function of the serum and neutrophils on the third day following Venoglobulin-IH administration, on the other hand, rose to 10 times that of the sera and neutrophils of patients with mild infections. The agglutinin titer of Venoglobulin-IH against S. intermedius and S. oralis were 32 and 16 times, respectively, indicating an evident rise in these titers against the clinical isolates in comparison with the reference strains of the same organisms. These findings indicated that the oral streptococci that are isolated from patients with grave infections are associated with an antigenicity that is different from the normal bacterial flora; and these organisms are more labile to phagocytosis by neutrophils that were obtained from patients who have been treated with Venoglobulin-IH.

Two types of stretch-activated channels coexist in the rabbit corneal epithelial cell

Ion channels contribute to the regulation of cellular function through control of the membrane potential and intracellular concentration of various ions. We examined stretch-activated channels in the corneal epithelial cell. Patch clamping was applied to enzymatically dissociated corneal epithelial cells to characterize their stretch-activated ion channels. The plasma membrane was stretched by applying suction to the patch pipette in cell-attached or inside-out patch configuration. The ion selectivity, voltage-dependence, and stretch-dependence were examined. Two kinds of stretch-activated channel events were observed; the previously-reported large conductance (L) channel and a novel small conductance (S) channel. The probability of recording L vs. S channels in the cell-attached configuration was about 2:1. The L channel was potassium selective with single channel conductance (gamma) of about 160 pS under the symmetrical (150 mm K+) solution. The S channel was permeable to Na+ and K+ with gamma of about 20 pS under the same conditions. Both L and S channels showed little activity in the absence of suction applied to the recording pipette. Channel activity was evoked by suction (negative pressure) stronger than -20 mmHg in both channels. The open probability (Po) and the mean current increased in proportion to further applied stretch and did not saturate for applied suction as strong as -80 mmHg, the pressure at which the gigaseal started to break. Thus, two types of stretch-activated channels coexist in corneal epithelial cells; a potassium-selective L channel and non-selective S channel. The contribution of these channels to the membrane potential is discussed.

Evaluation of combined therapy with chemoembolization and ethanol injection for advanced hepatocellular carcinoma

To evaluate the therapeutic efficacy of transcatheter arterial chemoembolization (TACE) combined with percutaneous ethanol injection therapy (PEIT) for advanced hepatocellular carcinoma, we studied the effectiveness of TACE therapy combined with PEIT (50 cases) and TACE alone (50 cases). In both groups, patients had multiple lesions, or a single lesion with a diameter exceeding 2 cm or with vascular invasion (stages II, III, and IV in the tumor staging classification of the Liver Cancer Study Group of Japan). The clinical features in the two groups were comparable. The cumulative survival rates with TACE-PEIT were 95.0% for 1 year, 72.5% for 2 years, and 50.0% for 3 years, whereas the rates with TACE alone were 92.5% for 1 year, 57.5% for 2 years, and 20.0% for 3 years. The survival rate in the TACE-PEIT group was significantly higher than that in the TACE alone group. Moreover, the survival rate of patients with stage II or III disease in the TACE-PEIT group was significantly better than that in the TACE alone group, and the survival rate of patients with Child's classification B or C in the TACE-PEIT group was significantly higher than that in the TACE alone group. Multivariate analysis using Cox's proportional hazard regression model showed that the most significant prognostic factors in the TACE-PEIT group were tumor embolus in the portal vein and the number of tumors. These results suggest the effectiveness of combining TACE and PEIT for the treatment of advanced hepatocellular carcinoma.

Fractionated stereotactic radiotherapy for choroidal melanoma

Stereotactic radiotherapy used for the treatment of choroidal melanoma made use of a 6-MeV linac with built-in multileaf collimators and a simple plastic head mold. The latter provided excellent head and ocular immobilization. The system resulted in highly localized dose distributions with a maximum 2-mm targeting error during fractionated treatments. Based on these techniques, sixteen patients with choroidal melanoma have so far been treated. Majority of patients received a total dose of 48 Gy in 8 fractions. Fourteen patients who presented with small- to moderate-sized tumors have remained free of relapse or major complications during the follow-up period of 3-42 months. Two patients who presented with an extensive tumor eventually required enucleation after irradiation. Technical precision required for stereotactic radiotherapy and reproducibility for fractionation appear adequate. Encouraging preliminary results justify further studies to evaluate its efficacy as an alternative to other conventional therapeutic approaches.

Electrophysiological characterization of cultured hepatic stellate cells in rats

This study aimed to examine electrophysiological properties of cultured rat hepatic stellate cells (HSCs) using the whole cell configuration of patch-clamp technique. At least three different current components were identified. First, when the membrane was depolarized to voltages more positive than -40 mV, a transient outward K+ current was evoked. Second, membrane hyperpolarization below -60 mV evoked a sustained and inward-rectifying K+ current. The third component was a current flowing outward, which was activated when the cell was depolarized more positively than 0 mV. The channel for this current allowed Na+, K+, and Cl- to pass nonspecifically, suggesting the presence of hemi gap-junctional channel. Furthermore, a laser photobleaching technique revealed the presence of gap junctions between adjacent HSCs. A voltage-gated Ca2+ current, which is known to occur in smooth muscle cells, was searched for but was not detectable. These results suggest that membrane potential of HSCs is determined specifically by the two distinct K+ channels and by an intercellular mechanism involving gap-junctional communication.

Elevation of serum creatine kinase during treatment with antithyroid drugs in patients with hyperthyroidism due to Graves disease. A novel side effect of antithyroid drugs

We describe 4 patients with Graves disease who had abnormal increases of serum creatine kinase (CK) concentrations during treatment with antithyroid medications. Three of the patients experienced myalgia and muscle cramps. All of the patients manifested an increase in serum CK levels 1 to 3 months after the administration of antithyroid drugs. Thyrotropin concentrations and cardiac systolic time indexes during the elevation of serum CK concentrations were not consistent with hypothyroidism. The mechanisms are not obvious, but it is likely that the rapid decrease of thyroid hormones in tissues may temporarily cause hypothyroid states, resulting in alterations in CK concentrations. It is suggested that hasty correction of thyrotoxicosis should be avoided in susceptible patients, unless the thyrotoxic conditions are critical.

Inhibition of peroxisome proliferator signaling pathways by thyroid hormone receptor. Competitive binding to the response element

Peroxisome proliferators (e.g. clofibric acid) and thyroid hormone play an important role in the metabolism of lipids. These effectors display their action through their own nuclear receptors, peroxisome proliferator-activated receptor (PPAR) and thyroid hormone receptor (TR). PPAR and TR are ligand-dependent, DNA binding, trans-acting transcriptional factors belonging to the erbA-related nuclear receptor superfamily. The present study focused on the convergence of the effectors on the peroxisome proliferator response element (PPRE). Transcriptional activation induced by PPAR through a PPRE was significantly suppressed by cotransfection of TR in transient transfection assays. The inhibition, however, was not affected by adding 3,5,3'-triiodo-L-thyronine (T3). Furthermore, the inhibition was not observed in cells cotransfected with retinoic acid receptor or vitamin D3 receptor. The inhibitory action by TR was lost by introducing a mutation in the DNA binding domain of TR, indicating that competition for DNA binding is involved in the molecular basis of this functional interaction. Gel shift assays revealed that TRs, expressed in insect cells, specifically bound to the 32P-labeled PPRE as heterodimers with the retinoid X receptor (RXR). Both PPAR and TR bind to PPRE, although only PPAR mediates transcriptional activation via PPRE. TR.RXR heterodimers are potential competitors with PPAR.RXR for binding to PPREs. It is concluded that PPAR-mediated gene expression is negatively controlled by TR at the level of PPAR binding to PPRE. We report here the novel action of thyroid hormone receptor in controlling gene expression through PPREs.

Nonselective suppression of voltage-gated currents by odorants in the newt olfactory receptor cells

Effects of odorants on voltage-gated ionic channels were investigated in isolated newt olfactory receptor cells by using the whole cell version of the patch-clamp technique. Under voltage clamp, membrane depolarization to voltages between -90 mV and +40 mV from a holding potential (Vh) of -100 mV generated time- and voltage-dependent current responses; a rapidly (< 15 ms) decaying initial inward current and a late outward current. When odorants (1 mM amyl acetate, 1 mM acetophenone, and 1 mM limonene) were applied to the recorded cell, the voltage-gated currents were significantly reduced. The dose-suppression relations of amyl acetate for individual current components (Na+ current: I(Na), T-type Ca2+ current: I(Ca), T, L-type Ca2+ current: I(Ca), L, delayed rectifier K+ current: I(KV) and Ca2(+)-activated K+ current: IK(Ca)) could be fitted by the Hill equation. Half-blocking concentrations for each current were 0.11 mM (INa), 0.15 mM (ICa,T), 0.14 mM (ICa,L), 1.7 mM (IKV), and 0.17 mM (IK(Ca)), and Hill coefficient was 1.4 (INa), 1.0 (ICa,T), 1.1 (ICa,L), 1.0 (IKV), and 1.1 (IK(Ca)), suggesting that the inward current is affected more strongly than the outward current. The activation curve of INa was not changed significantly by amyl acetate, while the inactivation curve was shifted to negative voltages; half-activation voltages were -53 mV at control, -66 mV at 0.01 mM, and -84 mV at 0.1 mM. These phenomena are similar to the suppressive effects of local anesthetics (lidocaine and benzocaine) on INa in various preparations, suggesting that both types of suppression are caused by the same mechanism. The nonselective blockage of ionic channels observed here is consistent with the previous notion that the suppression of the transduction current by odorants is due to the direst blockage of transduction channels.

A quinine-activated cationic conductance in vertebrate taste receptor cells

The chincona alkaloid quinine is known to be a bitter tasting substance for various vertebrates. We examined the effects of quinine on isolated taste receptor cells from the bullfrog (Rana catesbeiana). Membrane currents were recorded by whole-cell recording, while quinine hydrochloride was applied extracellularly from a puffer pipette. At the resting potential (-77 +/- 9 mV, mean +/- SD, n = 49 cells), taste cells generated inward currents in response to quinine stimulation (> 1 mM), indicating a depolarizing response in the taste cells. Two types of current responses were observed; a newly found quinine-activated cationic conductance and a previously reported blocking effect of quinine on K+ conductances. The cationic current was isolated from the K+ current by using a Cs(+)-containing patch pipette. The relative permeabilities (Pion) of the quinine-activated cationic conductance were: PNa/PK/PCs = 1:0.5:0.42. The quinine dose-response relation was described by the Hill equation with the K1/2 of 3.6 mM and Hill coefficient of 5.3. When extracellular [Ca2+] (1.8 mM) was reduced to nominally free, the conductance was enhanced by about sixfold. This property is consistent with observations on quinine responses recorded from the gustatory nerve, in vivo. The quinine-induced cationic current was decreased with an application of 8-bromo-cAMP. We conclude that the bitter substance quinine activates a cation channel in taste receptor cells and this channel plays an important role in bitter taste transduction.

T-type Ca2+ channel lowers the threshold of spike generation in the newt olfactory receptor cell

Mechanisms underlying action potential generation in the newt olfactory receptor cell were investigated by using the whole-cell version of the patch-clamp technique. Isolated olfactory cells had a resting membrane potential of -70 +/- 9 mV. Injection of a depolarizing current step triggered action potentials under current clamp condition. The amplitude of the action potential was reduced by lowering external Na+ concentration. After a complete removal of Na+, however, cells still showed action potentials which was abolished either by Ca2+ removal or by an application of Ca2+ channel blocker (Co2+ or Ni2+), indicating an involvement of Ca2+ current in spike generation of newt olfactory receptor cells. Under the voltage clamp condition, depolarization of the cell to -40 mV from the holding voltage of -100 mV induced a fast transient inward current, which consisted of Na+ (INa) and T-type Ca2+ (ICa.T) currents. The amplitude of ICa,T was about one fourth of that of INa. Depolarization to more positive voltages also induced L-type Ca2+ current (ICa,L). ICa,L was as small as a few pA in normal Ringer solution. The activating voltage of ICa,T was approximately 10 mV more negative than that of INa. Under current clamp, action potentials generated by a least effective depolarization was almost completely blocked by 0.1 mM Ni2+ (a specific T-type Ca2+ channel blocker) even in the presence of Na+. These results suggest that ICa,T contributes to action potential in the newt olfactory receptor cell and lowers the threshold of spike generation.