Chemotransduction in the carotid body: K+ current modulated by PO2 in type I chemoreceptor cells

The ionic currents of carotid body type I cells and their possible involvement in the detection of oxygen tension (Po2) in arterial blood are unknown. The electrical properties of these cells were studied with the whole-cell patch clamp technique, and the hypothesis that ionic conductances can be altered by changes in PO2 was tested. The results show that type I cells have voltage-dependent sodium, calcium, and potassium channels. Sodium and calcium currents were unaffected by a decrease in PO2 from 150 to 10 millimeters of mercury, whereas, with the same experimental protocol, potassium currents were reversibly reduced by 25 to 50 percent. The effect of hypoxia was independent of internal adenosine triphosphate and calcium. Thus, ionic conductances, and particularly the O2-sensitive potassium current, play a key role in the transduction mechanism of arterial chemoreceptors.

Bacteremic pneumonia due to Staphylococcus aureus: A comparison of disease caused by methicillin-resistant and methicillin-susceptible organisms

We performed a prospective study of all patients with bacteremic pneumonia due to Staphylococcus aureus over a period of 6 years during an outbreak of methicillin-resistant S. aureus (MRSA). Patients with bacteremic pneumonia due to MRSA (32 cases) or methicillin-susceptible S. aureus (MSSA; 54 cases) were compared. The patients with MRSA pneumonia were older and were more likely than those with MSSA pneumonia to have predisposing factors for acquisition of the infection. There were no differences in clinical findings, radiological pattern, or complications in clinical evolution among patients with MRSA and MSSA pneumonia. Mortality was significantly higher among MSSA-infected patients treated with vancomycin than among those treated with cloxacillin (47% vs. none; P<.01). Multivariate analysis (stepwise logistic regression method) showed a relationship between mortality and the following variables: septic shock (odds ratio [OR], 61), vancomycin treatment (OR, 14), and respiratory distress (OR, 8).

Lung cancer and arsenic concentrations in drinking water in Chile

Cities in northern Chile had arsenic concentrations of 860 microg/liter in drinking water in the period 1958-1970. Concentrations have since been reduced to 40 microg/liter. We investigated the relation between lung cancer and arsenic in drinking water in northern Chile in a case-control study involving patients diagnosed with lung cancer between 1994 and 1996 and frequency-matched hospital controls. The study identified 152 lung cancer cases and 419 controls. Participants were interviewed regarding drinking water sources, cigarette smoking, and other variables. Logistic regression analysis revealed a clear trend in lung cancer odds ratios and 95% confidence intervals (CIs) with increasing concentration of arsenic in drinking water, as follows: 1, 1.6 (95% CI = 0.5-5.3), 3.9 (95% CI = 1.2-12.3), 5.2 (95% CI = 2.3-11.7), and 8.9 (95% CI = 4.0-19.6), for arsenic concentrations ranging from less than 10 microg/liter to a 65-year average concentration of 200-400 microg/liter. There was evidence of synergy between cigarette smoking and ingestion of arsenic in drinking water; the odds ratio for lung cancer was 32.0 (95% CI = 7.2-198.0) among smokers exposed to more than 200 microg/liter of arsenic in drinking water (lifetime average) compared with nonsmokers exposed to less than 50 microg/liter. This study provides strong evidence that ingestion of inorganic arsenic is associated with human lung cancer.

Low pO2 selectively inhibits K channel activity in chemoreceptor cells of the mammalian carotid body

The hypothesis that changes in environmental O2 tension (pO2) could affect the ionic conductances of dissociated type I cells of the carotid body was tested. Cells were subjected to whole-cell patch clamp and ionic currents were recorded in a control solution with normal pO2 (pO2 = 150 mmHg) and 3-5 min after exposure to the same solution with a lower pO2. Na and Ca currents were unaffected by lowering pO2 to 10 mmHg, however, in all cells studied (n = 42) exposure to hypoxia produced a reversible reduction of the K current. In 14 cells exposed to a pO2 of 10 mmHg peak K current amplitude decreased to 35 +/- 8% of the control value. The effect of low pO2 was independent of the internal Ca2+ concentration and was observed in the absence of internal exogenous nucleotides. Inhibition of K channel activity by hypoxia is a graded phenomenon and in the range between 70 and 120 mmHg, which includes normal pO2 values in arterial blood, it is directly correlated with pO2 levels. Low pO2 appeared to slow down the activation time course of the K current but deactivation kinetics seemed to be unaltered. Type I cells subjected to current clamp generate large Na- and Ca-dependent action potentials repetitively. Exposure to low pO2 produces a 4-10 mV increase in the action potential amplitude and a faster depolarization rate of pacemaker potentials, which leads to an increase in the firing frequency. Repolarization rate of individual action potentials is, however, unaffected, or slightly increased. The selective inhibition of K channel activity by low pO2 is a phenomenon without precedents in the literature that explains the chemoreceptive properties of type I cells. The nature of the interaction of molecular O2 with the K channel protein is unknown, however, it is argued that a hemoglobin-like O2 sensor, perhaps coupled to a G protein, could be involved.

Oxygen and acid chemoreception in the carotid body chemoreceptors

The carotid bodies are arterial chemoreceptors that are sensitive to blood PO2, PCO2 and pH. They are the origin of reflexes that are crucial for maintaining PCO2 and pH in the internal milieu and for adjusting the O2 supply according to the metabolic needs of the organism in situations of increased demand, such as exercise and while breathing at decreased O2 partial pressures during ascent or when living at high altitude. Chemoreceptor cells of the carotid body transduce the blood-borne stimuli into a neurosecretory response that is dependent on external Ca2+. These cells have an O2-sensitive K+ current that is reversibly inhibited by low PO2. It is proposed that the depolarization produced by inhibition of this K+ current activates Ca2+ channels; Ca2+ influx and neurosecretion follow. The cells have also a potent Na(+)-Ca2+ antiporter that could be responsible for the intracellular Ca2+ rise required to trigger the release of neurotransmitters during high PCO2 or low pH stimulation.

Solution structure of gamma 1-H and gamma 1-P thionins from barley and wheat endosperm determined by 1H-NMR: a structural motif common to toxic arthropod proteins

The complete assignment of the proton NMR spectra of the homologous gamma 1-hordothionin and gamma 1-purothionin (47 amino acids, 4 disulfide bridges) from barley and wheat, respectively, has been performed by two-dimensional sequence-specific methods. A total of 299 proton-proton distance constraints for gamma 1-H and 285 for gamma 1-P derived from NOESY spectra have been used to calculate the three-dimensional solution structures. Initial structures have been generated by distance geometry methods and further refined by dynamical simulated annealing calculations. Both proteins show identical secondary and tertiary structure with a well-defined triple-stranded antiparallel beta-sheet (residues 1-6, 31-34, and 39-47), an alpha-helix (residues 16-28), and the corresponding connecting loops. Three disulfide bridges are located in the hydrophobic core holding together the alpha-helix and the beta-sheet and forming a cysteine-stabilized alpha-helical (CSH) motif. Moreover, a clustering of positive charges is observed on the face of the beta-sheet opposite to the helix. The three-dimensional structures of the gamma-thionins differ remarkably from plant alpha- and beta-thionins and crambin. However, they show a higher structural analogy with scorpion toxins and insect defensins which also present the CSH motif.

Vasoconstrictive effect of bile acids on isolated human placental chorionic veins

Intrahepatic cholestasis of pregnancy (ICP) is a rare complication of late pregnancy associated with a high rate of premature delivery, antepartum fetal death and fetal hypoxia. Since the principal biochemical feature of ICP is a marked elevation of maternal serum bile acid levels, a role of these substances in the pathophysiology of fetal complications has been suggested. In this study, the effect of bile acids on isolated human placental chorionic veins is described. High concentrations of bile acids, especially cholic acid, have a dose-dependent vasoconstrictive effect, which suggests that these substances could exert a detrimental effect on the fetus by increasing the resistance in chorionic veins through a vasospasm of the placental chorionic surface. An abrupt reduction of the oxygenated blood flow at the level of the placental chorionic plate may cause an acute impairment of the fetal perfusion and oxygenation, leading to fetal asphyxia. This is the first report that provides experimental evidence of the possible role of bile acids in those mechanisms that trigger fetal asphyxia in pregnancies complicated by ICP.

Gamma-tubulin is required for the structure and function of the microtubule organizing centre in Drosophila neuroblasts

We report that in Drosophila, gamma-tubulin is required for the structure as well as the function of microtubule organizing centres (MTOCs). This conclusion is based on the identification and phenotypic characterization of a mutant allele of the gamma-tubulin gene located at region 23C of the polytene chromosome map. This mutation, which we have called gamma-tub23CPl, is caused by the insertion of a P-element within the 5' untranslated leader of the gamma-tubulin transcript. Northern and Western analysis show that gamma-tub23CPl is either a null or a very severe hypomorph as no gamma-tubulin mRNA or protein can be detected in mutant individuals. Visualization of DNA, MTOCs and microtubules by confocal laser scanning microscopy of cells from individuals homozygous for gamma-tub23CPl reveals a series of phenotypic abnormalities. Some of these are similar to those observed after disruption of gamma-tubulin function in other organisms, including mitotic arrest and a dramatic decrease in the number of microtubules, but, in addition, we have observed that mutation in this gene also results in highly abnormal MTOCs which show a variety of shapes and sizes which we never observed in wild type cells. These results show that gamma-tubulin is required for both structural and functional roles in the MTOCs.

Vaccinia virus infection disrupts microtubule organization and centrosome function

We examined the role of the microtubule cytoskeleton during vaccinia virus infection. We found that newly assembled virus particles accumulate in the vicinity of the microtubule-organizing centre in a microtubule- and dynein-dynactin complex-dependent fashion. Microtubules are required for efficient intracellular mature virus (IMV) formation and are essential for intracellular enveloped virus (IEV) assembly. As infection proceeds, the microtubule cytoskeleton becomes dramatically reorganized in a fashion reminiscent of overexpression of microtubule-associated proteins (MAPs). Consistent with this, we report that the vaccinia proteins A10L and L4R have MAP-like properties and mediate direct binding of viral cores to microtubules in vitro. In addition, vaccinia infection also results in severe reduction of proteins at the centrosome and loss of centrosomal microtubule nucleation efficiency. This represents the first example of viral-induced disruption of centrosome function. Further studies with vaccinia will provide insights into the role of microtubules during viral pathogenesis and regulation of centrosome function.

High-resolution three-dimensional structure of ribonuclease A in solution by nuclear magnetic resonance spectroscopy

High-resolution three-dimensional structures of bovine pancreatic ribonuclease A in aqueous solution have been determined by nuclear magnetic resonance (NMR) spectroscopy combined with restrained molecular dynamics calculations. The structures are based on: (1) 464 interproton distance constraints with accurate upper and lower limits, determined from build-up rates of nuclear Overhauser effects (NOE) by using the complete relaxation matrix; (2) 999 more approximate upper limits for interproton distances; and (3) 42 dihedral angle constraints (37 for phi and 5 for chi 1). A total of 16 structures were calculated, which show a root-mean-square (r.m.s.) deviation of 0.66 A for the backbone atoms and 1.68 A for all heavy-atoms. The converged structures are highly similar to those found in the crystal state. r.m.s. deviation of backbone atom positions in the crystal as compared to those in the average solution structure is 0.92 A. Observed differences are concentrated in loop regions and in the neighborhood of His119 and His48 side-chains. Dynamic aspects, such as H/D amide proton exchange and side-chain mobility have been examined.

Bacteriocin AS-48, a microbial cyclic polypeptide structurally and functionally related to mammalian NK-lysin

The solution structure of bacteriocin AS-48, a 70-residue cyclic polypeptide from Enterococcus faecalis, consists of a globular arrangement of five alpha-helices enclosing a compact hydrophobic core. The head-to-tail union lies in the middle of helix 5, a fact that is shown to have a pronounced effect on the stability of the three-dimensional structure. Positive charges in the side chains of residues in helix 4 and in the turn linking helix 4 to helix 5 form a cluster that most probably determine its antibacterial activity by promoting pore formation in cell membranes. A similar five-helix structural motif has been found in the antimicrobial NK-lysin, an effector polypeptide of T and natural killer (NK) cells. Bacteriocin AS-48 lacks the three disulfide bridges characteristic of the saposin fold present in NK-lysin, and has no sequence homology with it. Nevertheless, the similar molecular architecture and high positive charge strongly suggest a common mechanism of antibacterial action.

O(2) modulates large-conductance Ca(2+)-dependent K(+) channels of rat chemoreceptor cells by a membrane-restricted and CO-sensitive mechanism

Hypoxic inhibition of large-conductance Ca(2+)-dependent K(+) channels (maxiK) of rat carotid body type I cells is a well-established fact. However, the molecular mechanisms of such inhibition and the role of these channels in the process of hypoxic transduction remain unclear. We have examined the mechanisms of interaction of O(2) with maxiK channels exploring the effect of hypoxia on maxiK currents recorded with the whole-cell and the inside-out configuration of the patch-clamp technique. Hypoxia inhibits channel activity both in whole-cell and in excised membrane patches. This effect is strongly voltage- and Ca(2+)-dependent, being maximal at low [Ca(2+)] and low membrane potential. The analysis of single-channel kinetics reveals a gating scheme comprising three open and five closed states. Hypoxia inhibits channel activity increasing the time the channel spends in the longest closed states, an effect that could be explained by a decrease in the Ca(2+) sensitivity of those closed states. Reducing maxiK channels with dithiothreitol (DTT) increases channel open probability, whereas oxidizing the channels with 2,2'-dithiopyridine (DTDP) has the opposite effect. These results suggest that hypoxic inhibition is not related with a reduction of channel thiol groups. However, CO, a competitive inhibitor of O(2) binding to hemoproteins, fully reverts hypoxic inhibition, both at the whole-cell and the single-channel level. We conclude that O(2) interaction with maxiK channels does not require cytoplasmic mediators. Such interaction could be mediated by a membrane hemoprotein that, as an O(2) sensor, would modulate channel activity.

Fundamental aspects of the nucleic acid i-motif structures

The latest research on fundamental aspects of i-motif structures is reviewed with special attention to their hypothetical rolein vivo.

Disease pattern of spondyloarthropathies in Spain: description of the first national registry (REGISPONSER) extended report

OBJECTIVE

The national registry of spondyloarthropathies (REGISPONSER) is launched to classify patients with this group of diseases treated in Spanish rheumatology clinics. This manuscript describes the methodological and organizational background as well as characteristics of patients finally included, and provides a comparative analysis between characteristics of both ankylosing spondylitis and undifferentiated spondyloarthropathy groups of patients.

PATIENTS AND METHODS

Twelve members of the GRESSER group have participated in the registry, for a one-year recruitment period. All consecutively registered adult patients treated in their clinics met the classification criteria of the European Spondyloarthropathies Study Group (ESSG). Data collected reflect the socio-demographic characteristics, as well as disease activity and functional status, clinical form at onset, treatment used and quality of life; all measured by standard instruments.

RESULTS

Throughout 1 yr, 1385 patients have been included in the registry: 939 males (68%) and 440 females (32%), with an average age of 47 +/- 13 years (mean +/- s.d.), and an average disease duration of 12 +/- 9 years. Diagnoses of the included patients were: AS (n = 842, 61%), PsA (n = 290, 21%), u-SpA (n = 205, 15%), reactive arthritis (n = 16, 1.2%), inflammatory bowel disease arthritis (n = 13, 0.9%) and JCA-spondyloathropathy (n = 13, 0.9%). Regarding clinical form, 54% had axial disease, 20% peripheral disease, 24% mixed disease and 0.6% isolated enthesitic form. Low-back pain was the first symptom reported in 53% of the patients, and most common extra-articular disease manifestations were psoriasis (25%), anterior uveitis (16%) and intestinal inflammatory disease (4%). Some kind of work disability was reported by 353 patients (25.5%).

CONCLUSIONS

Such databases are very useful to obtain information about characteristics of SpA patients treated in a certain location or following a specific treatment practice, and provide a tool for assessing the impact of the disease. Data collected in this registry provide an appropriate clinical and demographic profile of patients suffering from SpA in Spain.

Kvbeta1.2 subunit coexpression in HEK293 cells confers O2 sensitivity to kv4.2 but not to Shaker channels

Voltage-gated K+ (KV) channels are protein complexes composed of ion-conducting integral membrane alpha subunits and cytoplasmic modulatory beta subunits. The differential expression and association of alpha and beta subunits seems to contribute significantly to the complexity and heterogeneity of KV channels in excitable cells, and their functional expression in heterologous systems provides a tool to study their regulation at a molecular level. Here, we have studied the effects of Kvbeta1.2 coexpression on the properties of Shaker and Kv4.2 KV channel alpha subunits, which encode rapidly inactivating A-type K+ currents, in transfected HEK293 cells. We found that Kvbeta1.2 functionally associates with these two alpha subunits, as well as with the endogenous KV channels of HEK293 cells, to modulate different properties of the heteromultimers. Kvbeta1.2 accelerates the rate of inactivation of the Shaker currents, as previously described, increases significantly the amplitude of the endogenous currents, and confers sensitivity to redox modulation and hypoxia to Kv4.2 channels. Upon association with Kvbeta1.2, Kv4.2 can be modified by DTT (1,4 dithiothreitol) and DTDP (2,2'-dithiodipyridine), which also modulate the low pO2 response of the Kv4.2+beta channels. However, the physiological reducing agent GSH (reduced glutathione) did not mimic the effects of DTT. Finally, hypoxic inhibition of Kv4.2+beta currents can be reverted by 70% in the presence of carbon monoxide and remains in cell-free patches, suggesting the presence of a hemoproteic O2 sensor in HEK293 cells and a membrane-delimited mechanism at the origin of hypoxic responses. We conclude that beta subunits can modulate different properties upon association with different KV channel subfamilies; of potential relevance to understanding the molecular basis of low pO2 sensitivity in native tissues is the here described acquisition of the ability of Kv4. 2+beta channels to respond to hypoxia.

Nitric oxide mediates tumor necrosis factor-alpha cytotoxicity in endothelial cells

Tumor necrosis factor alpha (TNF-alpha) exerts multiple actions on endothelial cells including among others the expression of pro-coagulant activity and adhesion molecules, and secretion of cytokines. We now show that TNF-alpha induces a time- and dose-dependent cytotoxic effect on cultured bovine aortic endothelial cells. This TNF-induced cytotoxicity, which is preceded by increased production of nitric oxide (NO), is significantly decreased by the NO synthase inhibitor N-iminoethyl-L-ornithine (L-NIO). Dexamethasone, which prevents the expression of cytokine-induced NO synthase in endothelial cells, also inhibits TNF-alpha-dependent cytotoxicity. The results indicate that NO is involved in the cytotoxic effect of TNF-alpha on endothelial cells.

Hsp90 is a core centrosomal component and is required at different stages of the centrosome cycle in Drosophila and vertebrates

To determine the molecular composition of the centrosome of a higher eukaryote, we carried out a systematic nano-electrospray tandem or MALDI mass spectrometry analysis of the polypeptides present in highly enriched preparations of immunoisolated Drosophila centrosomes. One of the proteins identified is Hsp83, a member of the highly conserved Hsp90 family including chaperones known to maintain the activity of many proteins but suspected to have other essential, unidentified functions. We have found that a fraction of the total Hsp90 pool is localized at the centrosome throughout the cell cycle at different stages of development in Drosophila and vertebrates. This association between Hsp90 and the centrosome can be observed in purified centrosomes and after treatment with microtubule depolymerizing drugs, two criteria normally used to define core centrosomal components. Disruption of Hsp90 function by mutations in the Drosophila gene or treatment of mammalian cells with the Hsp90 inhibitor geldanamycin, results in abnormal centrosome separation and maturation, aberrant spindles and impaired chromosome segregation. This suggests that another role of Hsp90 might be to ensure proper centrosome function.

Periodontal pathogens in atheromatous plaques isolated from patients with chronic periodontitis

BACKGROUND AND OBJECTIVE

It has been suggested that chronic infections may predispose to cardiovascular disease. The relationship between periodontal disease and cardiovascular disease has been a subject of increasing research in recent years. The isolation and identification of periodontal bacteria from atheromatous plaque can contribute to our knowledge of this vascular disease. The aim of this study was to isolate and identify periodontal bacteria from the periodontal pockets of different patients and to compare them with the microorganisms detected in the atheromatous plaques obtained from the same patients.

MATERIAL AND METHODS

Clinical isolates were obtained from 12 patients with periodontal wounds and atheromathous plaques. These samples were cultured in the appropriate bacteriological culture media and incubated in an anaerobic system. Periodontal bacteria were identified using polymerase chain reaction (PCR) assays.

RESULTS

From the 12 patients studied, nine presented different periodontopathic bacterial species. In two, Actinobacillus actinomycetemcomitans was present in the periodontal pockets and the respective atheromatous plaques.

CONCLUSION

The presence of A. actinomycetemcomitans in atheromatous plaques and the periodontal pockets of the same patients could indicate a role for periodontal pathogenic bacteria in the atherosclerosis disease process.

Centrosomes and microtubule organisation during Drosophila development

Are the microtubule-organising centers of the different cell types of a metazoan interchangeable? If not, what are the differences between them? Do they play any role in the differentiation processes to which these cells are subjected? Nearly one hundred years of centrosome research has established the essential role of this organelle as the main microtubule-organising center of animal cells. But only now are we starting to unveil the answers to the challenging questions which are raised when the centrosome is studied within the context of a pluricellular organism. In this review we present some of the many examples which illustrate how centrosomes and microtubule organisation changes through development in Drosophila and discuss some of its implications.

Protection against Salmonella typhi infection in mice after immunization with outer membrane proteins isolated from Salmonella typhi 9,12,d, Vi

The current studies were undertaken to assess the ability of the outer membrane proteins (OMPs) of Salmonella typhi to induce protection against challenge with the bacteria in mucin. OMPs were isolated as described by Schnaitman (J. Bacteriol. 108:553-556, 1971) and were found to be contaminated with approximately 4% lipopolysaccharide (LPS). Immunization with as little as 30 micrograms of OMPs conferred 100% protection to mice challenged with up to 1,000 50% lethal doses (LD50) of two strains of S. typhi (9,12,d, Vi and Ty2). In addition, 30% protection against challenge with up to 500 LD50 of Salmonella typhimurium was achieved. Immunization with LPS at doses equivalent to those found in the OMPs was considerably inferior to the OMPs in the induction of an immune status. Moreover, LPS was effective only when the challenge was performed with S. typhi 9,12,d, Vi (40% protection to 100 LD50). An antiserum raised in rabbits reacted mainly against the bands of the molecular weights corresponding to the so-called porins contained in the OMP preparation as shown by Western blotting (immunoblotting). This rabbit antiserum protected 100% of mice against challenge with 100 LD50 of either strain of S. typhi and 80% of mice against challenge with the same LD50 of S. typhimurium. These results indicate the usefulness of OMPs in the induction of active immunity against S. typhi in mice.

Transcripts of one of two Drosophila cyclin genes become localized in pole cells during embryogenesis

Cyclins, originally discovered in the eggs of marine invertebrates, are proteins which undergo dramatic cycles of synthesis followed by degradation at the metaphase-anaphase transition of cell division. That they participate in the G2-M transition is supported by the fact that when synthetic cyclin messenger RNAs from clam and sea urchin are microinjected into the G2-arrested oocytes of Xenopus, they induce maturation. The cyclin of fission yeast is the product of the cdc13 gene, which is known to interact with cdc2, a gene required for the entry into mitosis. We have cloned the genes that encode A-type and B-type cyclins from Drosophila melanogaster by virtue of their sequence similarity to oligonucleotides corresponding to conserved regions of the cyclin genes. We show that both genes encode abundant maternal mRNAs, but whereas the cyclin A mRNA is relatively uniformly distributed before cell formation, the cyclin B mRNA becomes localized to the developing pole cells. In larvae, cyclin A is expressed predominantly in brain and imaginal disks, whereas cyclin B transcripts are abundant in testes.

Ionic currents in dispersed chemoreceptor cells of the mammalian carotid body

Ionic currents of enzymatically dispersed type I and type II cells of the carotid body have been studied using the whole cell variant of the patch-clamp technique. Type II cells only have a tiny, slowly activating outward potassium current. By contrast, in every type I chemoreceptor cell studied we found (a) sodium, (b) calcium, and (c) potassium currents. (a) The sodium current has a fast activation time course and an activation threshold at approximately -40 mV. At all voltages inactivation follows a single exponential time course. The time constant of inactivation is 0.67 ms at 0 mV. Half steady state inactivation occurs at a membrane potential of approximately -50 mV. (b) The calcium current is almost totally abolished when most of the external calcium is replaced by magnesium. The activation threshold of this current is at approximately -40 mV and at 0 mV it reaches a peak amplitude in 6-8 ms. The calcium current inactivates very slowly and only decreases to 27% of the maximal value at the end of 300-ms pulses to 40 mV. The calcium current was about two times larger when barium ions were used as charge carriers instead of calcium ions. Barium ions also shifted 15-20 mV toward negative voltages the conductance vs. voltage curve. Deactivation kinetics of the calcium current follows a biphasic time course well fitted by the sum of two exponentials. At -80 mV the slow component has a time constant of 1.3 +/- 0.4 ms whereas the fast component, with an amplitude about 20 times larger than the slow component, has a time constant of 0.16 +/- 0.03 ms. These results suggest that type I cells have predominantly fast deactivating calcium channels. The slow component of the tails may represent the activity of a small population of slowly deactivating calcium channels, although other possibilities are considered. (c) Potassium current seems to be mainly due to the activity of voltage-dependent potassium channels, but a small percentage of calcium-activated channels may also exist. This current activates slowly, reaches a peak amplitude in 5-10 ms, and thereafter slowly inactivates. Inactivation is almost complete in 250-300 ms. The potassium current is reversibly blocked by tetraethylammonium. Under current-clamp conditions type I cells can spontaneously fire large action potentials. These results indicate that type I cells are excitable and have a variety of ionic conductances. We suggest a possible participation of these conductances in chemoreception.