Overproduction of vascular endothelial growth factor/vascular permeability factor is causative in Crow-Fukase (POEMS) syndrome

Crow-Fukase or POEMS syndrome of polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes is a rare multisystem disorder of obscure pathogenesis that is associated with microangiopathy, neovascularization, and accelerated vasopermeability. We examined the levels of the vascular endothelial growth factor/vascular permeability factor (VEGF) in the serum and cerebrospinal fluid (CSF) from 10 patients with this syndrome. Serum VEGF levels were about 15-30 times those in control subjects or patients with Guillain-Barré syndrome (GBS), chronic inflammatory demyelinating polyneuropathy (CIDP), and other neurological disorders. The CSF VEGF levels, however, were similar to those found in GBS and CIDP. Elevated VEGF levels in the serum decreased in 7 patients with Crow-Fukase syndrome after conventional therapy. The principal isoform of VEGF in Crow-Fukase syndrome was VEGF165. Elevated VEGF was independent of M-protein. Our results suggest that the overproduction of VEGF is important in the pathogenesis of this disorder.

Identity of differentiation inducing factor and tumour necrosis factor

Human myelogenous leukaemic cells can be induced to differentiate into the monocyte/macrophage pathway by protein inducers called differentiation inducing factors (DIF) in conditioned media of mitogen-stimulated human peripheral blood leukocytes. However, human DIF has not yet been well characterized. DIF is known to be a T-cell lymphokine, as it can be obtained from the T-cell line HUT-102 and can be partially purified from medium conditioned by phytohaemagglutinin (PHA)-stimulated lymphocytes. We found that monocytes also produce factor(s) that induce differentiation of human myelogenous leukaemia cell lines to cells with macrophage-like characteristics. This factor(s) has activity different from that of colony-stimulating factor(s) or interferons. We have now purified a DIF to homogeneity from medium conditioned by PHA-stimulated leukocytes using a human myeloblastic leukemia cell line, ML-1, as target cells. The purified DIF has a relative molecular mass (Mr) of approximately 17,000, with an NH2-terminal sequence the same as that of human tumour necrosis factor (TNF). Recombinant human TNF (rHuTNF) induces differentiation of ML-1 cells and an anti-pDIF monoclonal antibody can neutralize both differentiation inducing activity and cytotoxic activity of DIF and rHuTNF. The findings indicate that one of the DIF(s) produced by leukocytes is probably TNF.

A full length cDNA clone for the alkaline protease from Aspergillus oryzae: structural analysis and expression in Saccharomyces cerevisiae

We have cloned and determined the nucleotide sequence of a cDNA fragment for the entire coding region of the alkaline protease (Alp) from a filamentous ascomycete Aspergillus oryzae. According to the deduced amino acid sequence, Alp has a putative prepro region of 121 amino acids preceding the mature region, which consists of 282 amino acids. A consensus sequence of a signal peptide consisting of 21 amino acids is found at the N-terminus of the prepro region. The primary structure of the mature region shares extensive homology (29%-44%) with those of subtilisin families, and the three residues (Asp 32, His 64 and Ser 221 in subtilisin BPN') composing the active site are preserved. The entire cDNA, coding for prepro Alp, when introduced into the yeast Saccharomyces cerevisiae, directed the secretion of enzymatically active Alp into the culture medium, with its N-terminus and specific activity identical to native Aspergillus Alp.

Cloning and expression in yeast of a cDNA clone encoding Aspergillus oryzae neutral protease II, a unique metalloprotease

The neutral protease II (NpII) from Aspergillus oryzae is a zinc-containing metalloprotease with some unique properties. To elucidate its structure, we isolated a full-length cDNA clone for NpII. Sequence analysis reveals that NpII has a prepro region consisting of 175 amino acids preceding the mature region, which consists of 177 amino acids. As compared with other microbial metalloproteases, NpII is found to be unique in that it shares only a limited homology with them around two zinc ligand His residues and that the positions of the other zinc ligand (Glu) and the active site (His) cannot be established by homology. When a plasmid designed to express the prepro NpII cDNA was introduced into Saccharomyces cerevisiae and the transformant was cultured in YPD medium (2% glucose, 2% polypeptone, 1% yeast extract), it secreted a proNpII. However, in a culture of the same medium containing 0.2 mM ZnCl2, it secreted a mature NpII with a specific activity and N-terminus identical to those of native NpII. This observation suggests that either an autoproteolytic activity or a yeast protease effected the processing.

Reduction of the slow inward current of isolated rat ventricular cells by thiamylal and halothane

The barbiturates and halothane exert a negative inotropic effect on the myocardium. A reduction in the slow inward current, carried mainly by calcium ions, is an important factor for the underlying mechanism because the calcium current during the action potential provides the calcium ions for accompanying contraction, supplies Ca ions to the sarcoplasmic reticulum for subsequent contractions, and induces Ca release from the store site. It has been suggested that reduction in the slow inward current caused by anesthetics is indicated by depression of the slow action potential of the partially depolarized myocardium. In order to assess directly the effect of anesthetics on the slow inward current, we carried out voltage clamp experiments with single isolated rat ventricular cells obtained by an enzymatic dissociation method. Thiamylal (10(-4) mol . l-1) and halothane (1%) decreased the slow inward current to 60 +/- 5% (mean +/- s.d., n = 8) and to 65 +/- 10% (mean +/- s.d., n = 8) of the control value, respectively, without changing the configuration of the current-voltage curve. The results provide further evidence for anesthetic reduction of the slow inward current of the myocardium, and suggest that the negative inotropic effect is at least partly due to the reduction in that current.

Molecular cloning of cDNA coding for human preprourokinase

A cDNA library was constructed in pBR322 from 18S to 20S mRNA that was extracted from human kidney cells, fractionated on oligo(dT)-cellulose column and sucrose-density gradient, and confirmed for urokinase production in Xenopus laevis oocytes. The Escherichia coli RR1 transformants were hybridized to synthetic oligonucleotide probe prepared according to the known amino acid sequence, Glu 73 to Glu 77 of human urinary urokinase chain B. The entire cloned cDNA covers a 2250-bp region, wherein the 1293-bp sequence codes for preprourokinase consisting of 431 amino acids, with the first 20 residues being a signal peptide. The 5'-untranslated region is at least 80 bp long and the 3'-untranslated region is longer than 850 bp.

SET binding factor 2 (SBF2) mutation causes CMT4B with juvenile onset glaucoma

The authors report a Japanese family segregating autosomal recessive Charcot-Marie-Tooth disease (CMT) with focally folded myelin, juvenile-onset glaucoma, and a nonsense mutation of SET binding factor 2 (SBF2). The consistent phenotypic features associated with SBF2 mutations are early-onset demyelinating neuropathy, myelin folding, and markedly decreased motor nerve conduction velocities; glaucoma associates with SBF2 nonsense mutations.

Restoration of miR-517a expression induces cell apoptosis in bladder cancer cell lines

The aim of this study was to find novel tumor suppressor microRNAs through screening genes epigenetically silenced by methylation in bladder cancer (BC) cell lines using microRNA microarrays. Since miR-517a and miR-520g, both located on chromosome 19q13.42, were found to highly up-regulated genes after treatment with a demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-dc), we hypothesized that they are tumor-suppressor microRNAs and performed a gain-of-function study using these mature microRNAs. The miR-517a restoration showed significant inhibition of cell proliferation in the transfectants compared to miR-control-transfected cells (p<0.0001 both in BOY and T24 cells). Furthermore, ectopic overexpression of miR-517a markedly induced apoptosis in the miR-517a-transfected BC cell lines. In addition, we carried out oligo microarray analysis using miR-517a transfectants and miR-control transfectants (BOY and T24), from which 35 down-regulated genes and 19 up-regulated genes were identified. These included amphiregulin (AREG) and BCL2-associated transcription factor 1, transcript variant 1 (BCLAF1), previously reported to be concerned with apoptosis, in both cell lines by miR-517a restoration. These data suggest that miR-517a functions as a tumor suppressor through inhibition of cell proliferation and induction of apoptosis under the regulation of AREG and/or BCLAF1 in BC cells. Anti-apoptotic effects may be maintained by down-regulation of miR-517a due to DNA hypermethylation in human BC cells, suggesting that restoration of miR-517a may be a novel therapeutic strategy for human BC.

Performance evaluation of radiologists with artificial neural network for differential diagnosis of intra-axial cerebral tumors on MR images

BACKGROUND AND PURPOSE

Previous studies have suggested that use of an artificial neural network (ANN) system is beneficial for radiological diagnosis. Our purposes in this study were to construct an ANN for the differential diagnosis of intra-axial cerebral tumors on MR images and to evaluate the effect of ANN outputs on radiologists' diagnostic performance.

MATERIALS AND METHODS

We collected MR images of 126 patients with intra-axial cerebral tumors (58 high-grade gliomas, 37 low-grade gliomas, 19 metastatic tumors, and 12 malignant lymphomas). We constructed a single 3-layer feed-forward ANN with a Levenberg-Marquardt algorithm. The ANN was designed to differentiate among 4 categories of tumors (high-grade gliomas, low-grade gliomas, metastases, and malignant lymphomas) with use of 2 clinical parameters and 13 radiologic findings in MR images. Subjective ratings for the 13 radiologic findings were provided independently by 2 attending radiologists. All 126 cases were used for training and testing of the ANN based on a leave-one-out-by-case method. In the observer test, MR images were viewed by 9 radiologists, first without and then with ANN outputs. Each radiologist's performance was evaluated through a receiver operating characteristic (ROC) analysis on a continuous rating scale.

RESULTS

The averaged area under the ROC curve for ANN alone was 0.949. The diagnostic performance of the 9 radiologists increased from 0.899 to 0.946 (P < .001) when they used ANN outputs.

CONCLUSIONS

The ANN can provide useful output as a second opinion to improve radiologists' diagnostic performance in the differential diagnosis of intra-axial cerebral tumors seen on MR imaging.

Action of enflurane on cholinergic transmission in identified Aplysia neurones

Effects of enflurane on the cholinergic transmission in Aplysia neurones were studied by current and voltage clamp methods. Acetylcholine (ACh) evoked three types of postsynaptic responses on different identified neurones: (1) a depolarizing response due to an increase in Na and K conductances (D-response), (2) a fast hyperpolarizing response due to an increase in C1 conductance (C1-response), and (3) a slow hyperpolarizing response due to an increase in K conductance (K-response). Enflurane altered neither the action potential nor the membrane resistance of the neurones but depressed the three ACh-induced responses, non-competitively, in a dose-dependent manner. The K-response was less suppressed than the other two. Blockade of the closed state of ion channel was suggested by a reduction in the first ACh response evoked 1 min after administration of enflurane. The anaesthetic facilitated the decay of the neurally evoked e.p.s.c. and i.p.s.c. in suggesting a reduction in the mean open time of the postsynaptic ion channel. It is concluded that enflurane depresses excitatory and inhibitory cholinergic transmission by reducing the postsynaptic currents.

Immunological abnormality in patients with lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is a rare hereditary disorder manifesting hyperammonemia induced by low levels of basic amino acids, these low levels being due to the impaired transport of these acids in the intestinal mucosa and the renal tubules. Low serum arginine levels and probably the consequently low in vivo levels of nitric oxide (NO), which against acts as a physiological and immunological mediator/modulator, are thought to influence the immunological status in patients with LPI. Accordingly, this study was conducted to. We found that patients with LPI had leukocytopenia, high serum IgG levels, a high ratio of CD44B4-positive lymphocytes (helper inducer) to CD42H4-positive lymphocytes (suppressor inducer), low levels of leukocyte phagocytic, cytotoxic, and natural killer cell activity, and increased spontaneous proliferation of lymphocytes. These results were probably the consequence of persistent low NO levels in vivo.

IL-5 mRNA expression in blood lymphocytes from patients with Kimura's disease and parasite infection

Blood lymphocytes from patients with eosinophilia are known to produce interleukin-5 (IL-5) with appropriate stimulation in vitro. To determine whether blood lymphocytes from these patients produce IL-5 in vivo, we tested the IL-5 mRNA expression in blood lymphocytes immediately after separation by reverse-transcriptase polymerase chain reaction (RT-PCR) method. We found that lymphocytes from eosinophilic patients expressed IL-5 mRNA, but lymphocytes from normal volunteers did not express the lymphokine. These findings suggest that in patients with eosinophilia, peripheral blood lymphocytes produce IL-5 in vivo.

Micronucleus test with cyclophosphamide using mouse peripheral blood reticulocytes

The usefulness of the micronucleus test using supravital staining of peripheral blood reticulocytes with acridine orange was evaluated in two laboratories after administering cyclophosphamide (CYP) as a model chemical by intraperitoneal injection (i.p.) to CD-1 mice. The frequencies of micronucleated peripheral reticulocytes (MNRETs) increased dose-dependently at each sampling time. There were no significant differences in the results obtained with this new method by the two laboratories. Although the induction of MNRETs was delayed by about 24 h compared to that of micronucleated polychromatic erythrocytes (MNPCEs) in the bone marrow, the frequencies of MNRETs and MNPCEs were almost identical at each optical sampling time, 24 h for MNPCEs and 48 h for MNRETs. Therefore, it is concluded that this method is a suitable alternative to that using femoral marrow cells.

Thyroid storm induced by TSH-secreting pituitary adenoma: a case report

Thyroid stimulating hormone-secreting pituitary adenomas (TSHomas) are uncommon tumors of the anterior pituitary gland. Patients with TSHomas may present with hyperthyroidism, but the incidence of thyroid storm due to TSHomas has yet to be determined. We report a rare case of thyroid storm caused by TSHoma in a 54-year-old woman. Preoperatively she had symptoms of excessive sweating and palpitation. Blood tests showed inappropriate secretion of TSH with blood TSH 6.86 μ U/mL, fT3 19.8 pg/mL, and fT4 5.95 ng/dL. Magnetic resonance imaging (MRI) revealed a pituitary tumor with maximum diameter of 13 mm that was extirpated through transsphenoidal route. After operation the patient was stuporous and thyroid storm occurred presenting with hyperthermia, hypertension, and tachycardia. It was well managed with nicardipine, midazolam, steroids, and potassium iodide. Immunohistochemical staining of tumor specimen was positive for TSH and growth hormone (GH). One year after operation, fT3 and fT4 levels were still high. As her tumor was diagnosed to be GH- and TSH-producing adenoma, octreotide injection therapy was started, which normalized thyroid hormone levels. This is the second reported case with thyroid storm due to TSHoma and emphasizes the importance of strategies with interdisciplinary cooperation for prevention of such emergency conditions.

Effect of fibroblast-derived differentiation inducing factor on the differentiation of human monocytoid and myeloid leukemia cell lines

A fibroblast-derived differentiation inducing factor (F-DIF) purified from medium conditioned by a human fibroblast cell line (WI-26VA4) induced differentiation of human monocytic leukemia cell lines (U-937, THP-1) into cells with macrophage characteristics. F-DIF alone induced the differentiation of ML-1 cells only marginally, but it synergistically increased the differentiation when combined with TNF. Interferon-gamma, tumor necrosis factor, GM-CSF, interleukin-1 and interlukin-4 synergistically enhanced the differentiation of U-937 cells when combined with F-DIF.

Regional venous outflow, blood volume, and sympathetic nerve activity during hypercapnia and hypoxic hypercapnia

We examined the changes in systemic blood volume and regional venous outflow from the splanchnic, coronary, and other remaining vascular beds in response to acute hypercapnia or hypoxic hypercapnia in dogs, using cardiopulmonary bypass and a reservoir. Hypercapnia (PCO2 = 105 mmHg) (1 mmHg = 133 Pa) and hypoxic hypercapnia (PO2 = 23 mmHg, PCO2 = 99 mmHg) caused marked decreases in systemic blood volume of 14 +/- 3 and 16 +/- 3 mL/kg in spleen-intact dogs, and 3 +/- 2 and 10 +/- 2 mL/kg in splenectomized dogs, respectively. Splanchnic venous outflow increased by 12% at 3.5 min hypercapnia, whereas it decreased by 60% at 3.5 min hypoxic hypercapnia. Coronary venous outflow increased by 85 and 400% at 3.5 min hypercapnia and hypoxic hypercapnia, respectively. Sympathetic efferent nerve activity revealed a significant augmentation during hypoxic hypercapnia and a relatively smaller increase (30% of the response to hypoxic hypercapnia) during hypercapnia. Carotid and aortic chemoreceptor and baroreceptor denervation attenuated significantly the response of systemic blood volume to hypercapnia and hypoxic hypercapnia. The regional venous outflow responses to hypercapnia were not altered after chemodenervation, but those to hypoxic hypercapnia were significantly attenuated after chemodenervation. These results suggest that acute hypercapnia and hypoxic hypercapnia caused a marked decrease in vascular capacitance owing primarily to an increase in sympathetic efferent nerve activity via chemoreceptor stimulation. They also indicate that blood flow to the splanchnic vascular bed during hypercapnia increased (even though the cardiac output was constant), whereas it increased to the extrasplanchnic and coronary vascular beds during hypoxic hypercapnia.

Hereditary motor and sensory neuropathy with myelin folding and juvenile onset glaucoma

OBJECTIVE

We describe three patients from a family with motor and sensory neuropathy accompanied by open-angle glaucoma.

BACKGROUND

Autosomal recessive demyelinating hereditary motor and sensory neuropathies (HMSN) include different disorders. To our knowledge, autosomal recessive HMSN has not been associated with juvenile onset glaucoma.

METHODS

Sural nerve pathology of the three patients were examined, and genetic analysis of the family was performed.

RESULT

- The most prominent pathologic finding was a highly unusual myelin abnormality consisting of irregular redundant loops and folding of the myelin sheath. The family survey supports autosomal recessive inheritance. The molecular analysis failed to demonstrate either linkage of the disease to MPZ gene, PMP22 gene, Cx32 gene, orEGR2 gene. Analysis did not establish linkage of the disease to the locus of CMT4A, 4B, and 4C genes.

CONCLUSION

The present cases may represent a new type of HMSN accompanied by juvenile onset glaucoma.

Thrombolytic properties of an inactive proenzyme form of human urokinase secreted from human kidney cells

The relative fibrin-binding, fibrinolytic and fibrinogenolytic properties of single-chain pro-urokinase, an inactive proenzyme form of human urokinase purified from cultured human kidney cells, and urokinase were compared. The affinity of single-chain pro-urokinase for fibrin was much higher than that of urokinase. In Vitro thrombolytic studies showed that single-chain pro-urokinase is approximately three times more potent in fibrinolysis than urokinase and that it does not degrade fibrinogen in the plasma at a concentration, at which complete plasma clot lysis takes place; whereas, urokinase extensively degrades the fibrinogen in the plasma. These specific, potent thrombolytic properties of single-chain pro-urokinase seem to be due to its high affinity for fibrin and to its conversion from the inactive single-chain form to the active two-chain form on the thrombus by the catalytic amount of plasmin generated during coagulation. This single-chain pro-urokinase obtained from human kidney cells by tissue culture should prove advantageous than urokinase in thrombolytic therapy.

Thrombolytic effect of single-chain pro-urokinase in a rabbit jugular vein thrombosis model

The thrombolytic effect of single-chain pro-urokinase (SCPU) was examined in the rabbit using a jugular vein thrombosis model. Infusion of a low dose (120,000 IU/kg) of either urokinase (UK) or SCPU did not produce any significant thrombolysis. However, UK administration at such a low dose caused 20% degradation of circulating fibrinogen. A high dose (480,000 IU/kg) caused significant thrombolysis. The degree of fibrinogenolysis was about 20% in SCPU, but about 80% in UK. The thrombolytic efficiency of SCPU was thus about 3 times larger than that of UK. Analysis of fibrinolytic parameters such as plasminogen, alpha 2-plasmin inhibitor, etc. suggested that UK caused systemic activation of the fibrinolytic system, but SCPU, locally limited activation on the fibrin surface (fibrinolysis). These results indicate that SCPU represents a highly efficient thrombolytic agent without producing fibrinogenolysis.

Formation of tubuloreticular inclusions in mitogen-stimulated human lymphocyte cultures by endogenous or exogenous alpha-interferon

Tubuloreticular inclusions (TRI) were induced in normal blood lymphocytes after incubation with Staphylococcus aureus Cowan 1 (STA), but they were not induced by pokeweed mitogen (PWM), as we reported previously. TRI were also induced in Raji cells when grown in the medium of STA culture. Alpha-interferon (alpha IFN) was detected only in the medium of STA culture and not in PWM culture. The cells of PWM cultures formed TRI when exposed to various concentrations of human leukocyte alpha IFN. The incidences of TRI-positive cells in the presence of 50-500 IU/ml of alpha IFN were 3-5% on day 2 and increased to 10% on day 7. On days 5-7 of the PWM cultures, plasmacytoid cells containing TRI were seen not infrequently. In the presence of a high concentration of alpha IFN (10,000 IU/ml), which was sufficient to inhibit cell growth and differentiation, the growth of the TRI region was not altered and the incidence of TRI-positive cells was 9% on day 2 and increased to 15% on day 7. Our observations suggest that the TRI formation in STA culture is attributable to the alpha IFN produced endogenously by STA-stimulated cells and that some relationship might exist between the incidences of TRI-positive cells in these mitogen-stimulated cultures and the biologic functions of IFN.

Regional venous outflow, blood volume, and sympathetic nerve activity during severe hypoxia

We examined the dynamic changes in venous outflow from the splanchnic, coronary, and remaining other vascular beds and changes in systemic blood volume (SBV) in response to severe hypoxia (PO2 = 17 mmHg) in dogs using cardiopulmonary bypass and a reservoir. Splanchnic venous outflow, which also includes renal outflow in this study, decreased by 40%, and coronary venous outflow increased by 400% at 3.5 min after initiating severe hypoxia. Severe hypoxia caused a marked decrease in SBV of 23 +/- 1 and 9 +/- 2 ml/kg in spleen-intact and splenectomized dogs, respectively. The decrease in SBV was attenuated by 60 (P less than 0.01) and 83% (P less than 0.01) after the carotid and aortic chemoreceptor denervation (which was accompanied by baroreceptor denervation) and after hexamethonium infusion (10 mg/kg), respectively. Sympathetic efferent nerve activity revealed a tremendous augmentation, which began to rise at a PO2 of 40 mmHg before chemoreceptor denervation and at a PO2 of 22 mmHg after denervation. These results show that severe hypoxia causes a marked decrease in SBV, 60% of which is caused by active splenic contraction, and suggest that the sympathetic efferent nerve activity, which is augmented by the stimulation of chemoreceptors as well as the central nervous system, contributes greatly to those hypoxic changes.

Changes in quality of life in patients with acromegaly after surgical remission - A prospective study using SF-36 questionnaire

Patients with acromegaly have a compromised quality of life (QOL). Modern surgical techniques have improved the surgical cure rate. However, there are no prospective studies reporting postoperative changes in QOL among patients cured solely by surgery. The aim of the present study was to determine the effect of surgery on QOL using the 36-item short form health survey (SF-36) questionnaire. SF-36 scores comprise 3 components: the physical component summary (PCS), the mental component summary (MCS) and role-social component summary (RCS). Included in this prospective cohort were 41 patients with acromegaly who underwent surgery alone and achieved postoperative normalization of insulin-like growth factor-1. All participants completed the SF-36 preoperatively and 1 year postoperatively. Preoperatively, RCS and 4 subscale scores (role physical, social functioning, role emotional, mental health) were below the set standards for the normal population. Postoperatively, the PCS and RCS scores did not change significantly, but the MCS score improved significantly (from 48.1 ± 11.3 to 51.7 ± 8.9, p=0.03). Further we compared the QOL of 26 patients whose nadir GH level was < 0.4 μg/L during postoperative oral glucose tolerance testing (complete remission group) with that of 15 patients whose nadir GH level was ≥ 0.4 μg/L (partial remission group). There were no significant differences between these groups in terms of PCS, MCS, RCS, or any subscale scores. In conclusion, surgical remission mostly improved the participants' mental condition. There was no difference in QOL between patients who achieved the new remission criteria and those who did not.

Reduction in the myocardial sodium current by halothane and thiamylal

Effects of two general anesthetics, halothane and thiamylal, on the fast sodium inward current (INa) of enzymatically isolated single rat ventricular cells were studied under current clamp and voltage clamp conditions. A suction pipette technique was used for potential measurement, current injection and internal perfusion of isolated cells. In current clamp experiments, sodium action potential was elicited in a Ca-free Co Krebs solution and the action potential was reduced by 0.5% halothane and 5 X 10(-5) M thiamylal. In voltage clamp experiments, the calcium current was suppressed by replacing Ca with Co and the potassium current was eliminated by replacing K with Cs and adding 4-aminopyridine and tetraethylammonium. Both anesthetics decreased INa, in a dose dependent manner, without changing the shape of the current-voltage curve. Halothane (1%) shifted the steady state inactivation curve in a negative direction along the potential axis by 8.5 +/- 2 mV (mean +/- S.D., n = 4). Thiamylal, 5 X 10(-5) and 10(-4) M, shifted the curve in a negative direction by 4.4 +/- 0.8 mV (n = 5) and 8.6 +/- 3.2 mV (n = 5), respectively. Both agents slightly reduced the maximum sodium conductance (gNa). Halothane (1%) increased half recovery time from inactivation measured at -80 mV from 30 +/- 15 to 80 +/- 25 ms (n = 4). Thiamylal (10(-4) M) prolonged it at - 75 mV from 50 +/- 20 to 110 +/- 15 ms (n = 5). With a test pulse duration of 50 ms, neither drug produced a use-dependent inhibition of INa. Halothane and thiamylal depress the INa of cardiac muscles mainly by shifting the steady state inactivation curve in a negative direction along the potential axis. Relatively small prolongation of half recovery time from inactivation and no sign of use-dependent inhibition suggest a molecular mechanism which differs in some respects from the local anesthetics.