Modifications of the distribution of substance P-like immunoreactivity in the cerebral basal nuclei of the cat after electroacupuncture

The distribution of Substance P in the fibrillar structures of the basal nuclei of the cat brain, and its modification with low frequency electroacupuncture (EA) stimulation, have been studied using the indirect immunocytochemistry technique. An increase in the immunoreactivity of Substance P (IR-SP) after stimulation with EA has been observed in the nucleus caudatus and nucleus putamen, in the globus pallidus, and in the amygdaloid complex. Abundant IR-SP fibres have also been seen in some areas of the internal capsule. These observations place the said IR-SP modifications in the basal nuclei of the cat brain, when subjected to low frequency EA.

Hydrodynamic properties and immunological identification of the sodium- and chloride-coupled glycine transporter

We have recently reported the purification of the native sodium- and chloride-coupled glycine transporter from pig brain stem (López-Corcuera, B. Vázquez, J., and Aragón, C. (1991) J. Biol. Chem. 266, 24809-24814). This preparation is essentially homogeneous and contains a unique 100-kDa polypeptide based on electrophoretic migration under denaturing conditions. In this paper we report the hydrodynamic characterization of the native transporter, solubilized in two different detergents, as well as the immunological identification of the protein. On the basis of results obtained from size-exclusion chromatography, we calculated the Stokes radii of transporter 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS) and transporter-cholate complexes to be 5.5 and 6.0 nm, respectively. In addition, from H2O/D2O sucrose density gradient sedimentation analysis, we calculated the molecular weight of protein-detergent complexes to be 115,000 and 160,000 in CHAPS and cholate, respectively, and the molecular weight of the protein moiety as 86,000. Finally, polyclonal antibodies raised against the 100-kDa polypeptide were found to immunoprecipitate specifically glycine transport activity. Taken together, the results reported herein corroborate the identity of the 100-kDa band as the sodium- and chloride-coupled glycine transporter and also suggest that in its native state the transporter is a monomeric protein.

Cutaneous manifestations in Kartagener's syndrome: folliculitis, nummular eczema and pyoderma gangraenosum

We report the case of a 47-year-old male with Kartagener's syndrome (KS; situs inversus, bronchitis and sinusitis) who showed three types of cutaneous lesions: recurrent outbreaks of nummular eczema, recurrent deep folliculitis and two episodes of pyoderma gangraenosum. The patient had also IgA gammopathy of undetermined significance. This is the second case of KS associated with cutaneous lesions published so far and suggests that primary ciliary dyskinesia syndromes may have skin symptoms.

Bacterial single-chain antibody fragments, specific for carcinoembryonic antigen

We have produced single-chain antibody (scFv) fragments in bacteria specific for carcinoembryonic antigen (CEA). Polymerase chain reaction (PCR) was used for the cloning and modification of the heavy and light variable regions (VH and VL) of the mouse monoclonal antibody (MAb) CB-CEA.1. A 14-amino acid linker was used in the synthesis of the scFv gene. The VH and VL regions were amplified from cDNA by PCR using 5' end FR1 and 3' end constant region primers, and then sequenced. VH was then amplified by PCR using an exact 5' end FR1 primer, and a phosphorylated (PP) 3' end primer for J2 that also encoded the first 7 amino acids of the linker. VL was amplified with a PP 5' end primer for FR1, also encoding the remaining 7 amino acids of the linker, and a 3' end primer for J5, plus a stop codon and a BglII restriction site. The fragments were ligated and reamplified with the PP VH 5' and VL 3' end primers. The VH-linker-VL structure was blunt-cloned into expression vectors bearing the tryptophan promoter and pelB or ompA signal peptide sequences. Culture supernatant, bacteria pellet and periplasm preparations were assayed in Western blot and a protein of about 27 kDa was identified with rabbit antibodies specific for the Fab of CB-CEA.1. Bacterial supernatant and periplasm preparations also inhibited the recognition of CEA by HRP-labeled CB-CEA.1 in enzyme-linked immunosorbent assay (ELISA). Periplasm preparations were purified by affinity chromatography with specific anti-idiotypic MAbs. The Western blot of the eluates identified a protein of approximately 27 kDa that blocked the recognition of CEA by HRP-labeled CB-CEA.1 in ELISA. The VH-linker-VL structure was cloned into a vector bearing the lacZ promoter and the pelB signal peptide. The recombinant bacterial clones also expressed about 27 kDa scFv, specific for CEA.

Primary idiopathic osteolysis: description of a family

A clinical, analytical, and radiological study was carried out on three members of the same family with multicentric idiopathic osteolysis. Transmission appeared to be via the dominant autosome present in the mother and two daughters. In the daughters osteolysis was seen in the carpal and tarsal bones, whereas in the mother radiology showed it to be in the phalanges of the hands and feet.

Genetic diversity of penicillin-resistant Neisseria meningitidis

The genetic relatedness of 42 penicillin-resistant Neisseria meningitidis isolates obtained during a 2-year period from a single hospital was studied by multilocus enzyme electrophoresis and by restriction fragment length polymorphism (RFLP) analysis of penicillin-binding protein (PBP) 2 genes. The PBP 2 genes of 7 susceptible strains gave identical RFLP profiles. Sixteen different PBP 2 RFLP profiles were found among the 42 resistant strains, but 4 were found in greater than 1 resistant isolate. Multilocus enzyme electrophoresis revealed a high level of genetic diversity. Four clusters of resistant strains could be distinguished at a genetic distance of 0.75. Resistant strains with the most common PBP 2 RFLP profile were restricted to one of these clusters and may be derived from a common ancestral strain. However, resistant strains with the 3 other common RFLP profiles were distributed in two or more of the clusters.

Evidence of the presence of spotted fever group rickettsiae in dogs and dog ticks of the central provinces in Spain

To assess canine exposure to spotted fever group rickettsiae in the central provinces of Spain, ticks removed from dogs were studied by immunofluorescence (IF) staining. Twenty-eight out of 65 (43.0%) samples from ticks were positive. Sera from 58 dogs were also collected and the presence of antibodies to Rickettsia conorii studied. Thirty-four (58.6%) dogs presented significant titers by IF. Surveillance data from these provinces show the presence of Boutonneuse fever cases during recent years, evidence that dogs could serve as an indicator of rickettsial activity in these areas.

[Epidemic outbreak of viral meningitis caused by type 30 ECHO virus]

The clinical records of 15 children admitted to Hospital Infantile de México Federico Gómez with diagnosis of viral meningitis were reviewed. They were part of 19 patients admitted with this diagnosis during a 5 week period (March 22 to April 30, 1992) and represent a significant increase of aseptic meningitis compared with the same periods of previous years at Hospital Infantile de Mexico and in Mexico City where there is an ongoing epidemic outbreak of this entity. All the patients studied had spinal fluid findings consistent with viral meningitis and in 4 of them on ECHO virus type 30 was isolated at the Enterovirus Section of the CDC, Atlanta Georgia USA.

c-fos proto-oncogene changes in relation to REM sleep duration

Auditory stimulation has been shown to increase REM sleep periods in cats and humans. This effect has been attributed to an elevation of the level of excitability in a variety of brain stem neuronal groups. Fos-like immunostaining (FLI) has been useful in constructing maps of post-synaptic neuronal activity with single cell resolution, and has been suggested to be tightly correlated with ongoing neuronal activity. This study used FLI to quantify neurons from structures expressing c-fos in brain stem areas in animals with normal REMs and compared them with those showing extended REM periods. The results basically indicated that brain stem areas which in other studies have been described as having REM-ON cells, showed an increase in FLI, while no FLI changes occurred in areas described as having REM-OFF cells. These results are discussed in terms of the possibility that REM maintenance is related to a widespread increase in brain stem excitability.

Total anomalous pulmonary venous connection in adults. Long-term follow-up

Between 1961 and 1989, 19 patients with total anomalous pulmonary venous connection underwent surgical correction. Ages ranged from 18 to 38 years (mean 26.2 +/- 6.5 years). The anatomic variants included 10 patients with total anomalous pulmonary venous connection to the vertical vein, 6 patients with total anomalous pulmonary venous connection to the coronary sinus, and 2 with total anomalous pulmonary venous connection directly to the right atrium. The last patient had mixed connection to the coronary sinus and left vertical vein. Two patients died, one because of left atrial rupture and another of low cardiac output. Long-term follow-up after surgical repair ranged from 2 to 24 years (mean 7 +/- 6.2 standard deviation). Preoperative disability, assessed according to New York Heart Association criteria, showed 12 patients in functional class II and seven in class III. After treatment, 16 patients were in class I and one in class II (p less than 0.001). Echocardiographic evaluation of six patients revealed in all a normal left ventricular ejection fraction; the diastolic function was also normal except in one patient. The postoperative evaluation of the pulmonary arterial systolic pressure performed by both Doppler echocardiography and right cardiac catheterization in 14 patients showed a significant reduction of the mean pulmonary arterial systolic pressure from 51.1 +/- 3.4 to 37.4 +/- 14.4 mm Hg (p less than 0.01). The remaining three patients evaluated in the follow-up period only by clinical examination are in New York Heart Association functional class I. The anatomic characteristics of our patients were responsible for the long-term outcome without correction. Surgical treatment of older patients can be performed with satisfactory results and excellent long-term survival.

Sensitive procedures for measuring chloride fluxes mediated by the purified glycine receptor incorporated into phospholipid vesicles

Two novel methods have been developed to directly measure chloride influx into purified glycine receptor-containing phospholipid vesicles. Using a method based on the fluorescence quenching of a chloride-sensitive probe entrapped into the vesicles, a chloride influx was detected which could be enhanced by glycine and completely abolished by the antagonist strychnine. In addition, by tracing the 36Cl- influx into the proteoliposomes, a stimulatory effect of both glycine and beta-alanine could be seen, which can be inhibited by strychnine and other glycine antagonists. These data, together with a previous report demonstrating ligand-mediated iodide fluxes in the same preparation (Biochemistry, 28 (1989) 6405-6409), clearly demonstrate the utility of the reconstituted receptor preparation to investigate some ion channel and pharmacological properties of the glycine receptor.

[Portal venous flow as a prognostic factor in biliary atresia. A preliminary study]

Early prognosis factors determination is an important objective after Kasai's operation for biliary atresia repair. Serologic test, postoperative biliary flow, histologic studies and clinical manifestations provides adjunctive information. Hemodynamic patterns in biliary atresia where described in 80's before liver transplantation. This preliminary report evaluates portal flow velocity, hepatic arterial resistance and portal calibre in these patients. A prospective sonographic investigation was performed in ten children with biliary atresia. Hemodynamic findings and hepatobiliary function were compared in order to establish prognosis. All our patients with good prognosis had hepatopedal portal flow greater than 14 cm/sg, and arterial resistance between 0.68-0.78. Four patients with poor prognosis had hepatopedal flow lesser than 14 cm/sg or hepatopedal flow an resistance in hepatic artery was greater than 0.80.

Purification of the sodium- and chloride-coupled glycine transporter from central nervous system

We have recently developed a reconstitution assay which allows the rapid determination of sodium- and chloride-dependent glycine transport activity of many fractions (López-Corcuera, B., and Aragón, C. (1989) Eur. J. Biochem. 181, 519-524). In this paper we report the purification of the sodium- and chloride-coupled glycine transporter from pig brain stem. Transporter is solubilized from plasma membrane vesicles with 2% cholate and purified by sequential chromatography on phenyl-Sepharose, wheat germ agglutinin-Sepharose, and hydroxylapatite columns, followed by a 5-20% sucrose density gradient fractionation. Taking into account the inactivation suffered by the transporter, a final increase in specific activity of about 450-fold is achieved. Although two polypeptides with apparent molecular masses of 100 and 37 kDa are progressively enriched during the chromatographic steps, only the 100-kDa band comigrates with transport activity along the density gradient. This band is finally isolated to apparent homogeneity in the active fractions. We conclude that the 100-kDa band represents the glycine transporter. Finally, the pure transporter can be reconstituted into liposomes, retaining the absolute dependence on sodium and chloride gradients, the electrogenicity, the glycine affinity, the substrate specificity, and the sensitivity to group-selective modifiers characteristic of the native transporter.

Characterization of the solubilized charybdotoxin receptor from bovine aortic smooth muscle

Monoiodotyrosine ([125I]ChTX) binds with high affinity to a single class of receptors present in bovine aortic smooth muscle sarcolemmal membranes that are functionally associated with the high-conductance Ca(2+)-activated K+ channel [maxi-K channel; Vázquez, J., et al. (1989) J. Biol. Chem. 265, 20902-20909]. Cross-linking experiments carried out with this preparation in the presence of [125I]ChTX and disuccinimidyl suberate indicate specific incorporation of radioactivity into a protein of Mr 35,000. The smooth muscle ChTX receptor can be solubilized in active form in the presence of selected detergents. Treatment of membranes with digitonin releases about 50% of the ChTX binding sites. The solubilized receptor retains the same biochemical and pharmacological properties that are characteristic of toxin interaction with membrane-bound receptors. The solubilized receptor binds specifically to wheat germ agglutinin-Sepharose resin, suggesting that it is a glycoprotein. Functional ChTX binding sites can also be solubilized in 3-[(3-cholamidopropyl)dimethylamino]-1-propanesulfonate (CHAPS). Sucrose density gradient centrifugation of either digitonin or CHAPS extracts indicates that the ChTX receptor has a high apparent sedimentation coefficient (s20,w = 23 and 18 S, respectively). Cross-linking experiments indicate that the appearance of the 35-kDa membrane protein correlates with ChTX binding activity after both wheat germ agglutinin-Sepharose and sucrose density gradient centrifugation steps. Given the high apparent sedimentation coefficient of the ChTX receptor, the 35-kDa membrane protein may be a subunit of a higher molecular weight complex which forms the maxi-K channel in smooth muscle sarcolemma.

[Hepatic artery thrombosis in the pediatric liver transplant]

The hepatic artery thrombosis (HAT) is the most serious complication after pediatric liver transplantation. Most of the cases will need a retransplantation. Multiple factors are keeping in discussion as causes of this complication: Rejection, two or more arteries, complex vascular reconstruction, etc. This article describes our experience with this complication and the prophylactic treatment. From January 1986 through April 1991, 62 orthotopic liver transplants were performed on 48 pediatric patients with a mean age of seven years. The incidence of hepatic artery thrombosis was 19 per 100, increasing when recipients were less than three years and less than 15 kg (23.8 per 100). Forty six cases were rearterialized with end-to-end anastomoses, ten were rearterialized by directly anastomosing them to the recipient aorta and six with iliac artery graft. We use in the last 38 consecutive patients prophylactic heparin during two weeks after transplantation (300 u/kg/d) following with antiaggregants. There were eleven patients with hepatic artery thrombosis, one of them had two episodes in both grafts. We perform a retransplantation in eight patients, two died waiting a new graft and one exceptional patient is out of the clinic with normal liver function and without regraft. Seventeen grafts had two or more arteries from aorta, ten with branches from superior mesenteric artery and five from gastric artery. One graft had a triple hepatic artery and another one was a common hepatic artery from superior mesenteric artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfhydryl groups modulate the allosteric interaction between glycine binding sites at the inhibitory glycine receptor

We have investigated the effect of chemical reagents that modify sulfhydryl groups on the ligand binding properties of the glycine receptor (GlyR). The Hill coefficient (nH) for the displacement of [3H]strychnine binding by glycine was increased from approximately 0.8 to values significantly above 1 (approximately 1.2-1.4) in membranes pretreated with the disulfide-reducing agent dithiothreitol or glutathione. However, the affinity of strychnine or glycine for the GlyR was not affected by these treatments. This indicates that several glycine binding sites interact cooperatively for displacing bound strychnine under such experimental circumstances. A similar increase in the nH for glycine has been observed when the temperature of the binding assay was increased to 37 degrees C. Combination of dithiothreitol pretreatment and increased binding temperature led to nH variations similar to those observed with either of these treatments alone, a finding suggesting that their mechanisms of action are not independent. Conversely, modification of rat spinal cord membranes or of purified and reconstituted GlyR preparations with the sulfhydryl-alkylating agent N-ethylmaleimide or fluorescein-maleimide decreased nH values to approximately 0.5, without affecting glycine or strychnine affinities. This effect may be caused by an increased heterogeneity of GlyR populations. It is interesting that occupancy of the receptor by glycine or beta-alanine (but not by antagonists) specifically protects from the effects of the different sulfhydryl reagents. Moreover, the presence of some of the Eccles' anions, i.e., anions that permeate through the channels associated with GlyRs and gamma-aminobutyric acidA receptors, seems to be required for the action of both dithiothreitol and N-ethylmaleimide.(ABSTRACT TRUNCATED AT 250 WORDS)

[Histopathology of biliary atresia: correlation with biliary flow]

The objective of KASAI's operation is to obtain a postoperative bile excretion and to maintain an internal biliary fistula. The purpose of this report is to study the relationship between the liver histopathology and the postoperative bile flow and survival. From july 1976 to january 1990, 66 patients underwent a corrective operation for biliary atresia. In 24 patients we performed a KASAI's operation with internalization of the biliary conduit, 36 with externalization, four gall-bladder KASAI and two liver biopsy. The mean age at operation was 66 days and postoperative bile excretion was obtained in 43 of them (66 per 100). The survival rate was 70 per 100. The liver histopathology shown: minimum portal fibrosis (7.8 per 100), moderate (49 per 100) and severe (43 per 100). We found bile ducts in 30 patients (46 per 100), in three bile ducts were less than 50 mu, in 15 between 50 and 100 mu and more than 100 mu in 12. We did not found statistic correlation between grade of liver fibrosis size of bile duct and postoperative flow. We found a statistic correlation between the presence of bile ducts and postoperative flow (p less than 0.05).

Characterization of high affinity binding sites for charybdotoxin in synaptic plasma membranes from rat brain. Evidence for a direct association with an inactivating, voltage-dependent, potassium channel

Charybdotoxin (ChTX), a potent peptidyl inhibitor of several types of K+ channels, binds to sites in vascular smooth muscle sarcolemma (Vázquez, J., Feigenbaum, P., Katz, G. M., King, V. F., Reuben, J. P., Roy-Contancin, L., Slaughter, R. S., Kaczorowski, G. J., and Garcia, M. L. (1989) J. Biol. Chem. 265, 20902-20909) which are functionally associated with a high conductance Ca2(+)-activated K+ channel (PK,Ca). 125I-ChTX also binds specifically and reversibly to a single class of sites in plasma membranes prepared from rat brain synaptosomes. These sites exhibit a Kd of 25-30 pM, as measured by either equilibrium or kinetic binding protocols and display a maximum density of about 0.3-0.5 pmol/mg of protein. Competition studies with native ChTX yield a Ki of 8 pM for the noniodinated toxin. The highest density of ChTX sites exists in vesicle fractions of plasma membrane origin. Binding of 125I-ChTX is modulated by metal ions that interact with K+ channels: Ba2+, Ca2+, and Cs+ cause inhibition of ChTX binding; Na+ and K+ stimulate binding at low concentration before producing complete inhibition as their concentration is increased. Stimulation of binding is due to an allosteric interaction that decreases Kd whereas inhibition results from an ionic strength effect. Tetraethylammonium ion has no effect on binding, but tetrabutylammonium ion blocks binding with a Ki of 2.5 mM. Different toxins (i.e. alpha-dendrotoxin, noxiustoxin) that inhibit an inactivating, voltage-dependent K+ channel (PK,V) block 125I-ChTX binding in brain. In marked contrast, iberiotoxin, a selective inhibitor of PK,Ca, has no effect on ChTX binding in this preparation. Inhibition of ChTX binding by alpha-dendrotoxin and noxiustoxin results from an allosteric interaction between separate binding sites for these agents and the ChTX receptor. Taken together, these results suggest that the ChTX sites present in brain are associated with PK,V rather than with PK,Ca. Therefore, 125I-ChTX is a useful probe for elucidating the biochemical properties of a number of different types of K+ channels.

[Infection as a complication of the liver transplant]

Currently, the incidence of one episode of infection after liver transplantation is 83 for 100 and 50 for 100 of them are severe. We have studied 30 patients who underwent liver transplantation, ten of them received a second graft. All patients were treated prophylactic with antibiotics 48 hours and selective bowel decontamination, in 23 we used ganciclovir prophylactic. The incidence of infection was 73 for 100, 40 episodes of bacterial infection, eight fungal and ten viral. The direct relationship of infection and mortality was seen in six patients. We studied different risk factors of infection and we found a correlation between surgical time, prior operations and arterial thrombosis with infections.

Yersinia enterocolitica serotype O:3 is arthritogenic for mice

It is shown, for the first time, that Yersinia enterocolitica serotype O:3 is experimentally arthritogenic. Moreover, it is arthritogenic for the mouse, an optimal model for human yersiniosis. This arthritis can be induced by the oral route, the most common route in man. The pattern of joint disease closely parallels that of human reactive arthritis associated with this pathogen.

[Cryptorchism associated with hereditary nephritis: a 3-generation study in a Puerto Rican family]

Twenty three members of a family affected by Alport disease were studied throughout three generation. The incidence of auditory, ocular and hematological manifestation was low. It was found that four males with nephritis also had cryptorchism. This is a documentation of the previously unrecorded occurrence of cryptorchism associated with familiar nephritis. The characteristics of this pedigree are described and a review of the literature is presented.

[The pediatric liver transplant. The surgical aspects]

The Liver Transplant Program was begun at "La Paz" Children's Hospital on January 1986 after a long period of experimental activities. This was the first experience in the Madrid Community. From January 1986 to June 1989 we made 32 orthotopic liver transplants in 25 patients, seven received a second graft and one them received a liver segment because the donor had a large liver. 114 patients were evaluated but only 84 were considered candidates for liver transplantation. The different diseases of the transplants were: biliary atresia (9), Alagille syndrome (4), deficit alpha 1-antitrypsin (3), autoimmune hepatitis (2), neonatal hepatitis (1), Byler disease (1), Wolman disease (1). absent bile ducts (1), Wilson disease (1). Surgical technique was the same that has been described by Starzl using Eurocollins and lactate Ringer. In the 100% we made multiorgan procurement, liver and kidneys, 7% with heart and two heart-lung with hypothermia. In one occasion the donor operation was done out of the country (RFA--Düsseldorf). We never used by-pass during anhepatic phase. Arterial reconstruction was done by end-to-end anastomosis and in five patients we used aortic graft. Our arterial thrombosis rate was 18%. In one patient the portal vein was atrophic and we used a femoral graft between superior mesenteric vein and donor portal vein. For biliary reconstruction we used Roux-en-Y with intraluminal stent in 18 cases and choledocho-choledochus anastomosis in seven cases. Four patients had biliary complications: two biliary fistulas secondary to arterial thrombosis, biliary stenosis and bowel perforation by the intraluminal stent.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of high affinity binding sites for charybdotoxin in sarcolemmal membranes from bovine aortic smooth muscle. Evidence for a direct association with the high conductance calcium-activated potassium channel

Charybdotoxin (ChTX), a peptidyl inhibitor of the high conductance Ca2+-activated K+ channel (PK,Ca), has been radiolabeled to high specific activity with 125I, and resulting derivatives have been well separated. The monoiodotyrosine adduct blocks PK,Ca in vascular smooth muscle with slightly reduced potency compared with the native peptide under defined experimental conditions. [125I]ChTX, representing this derivative, binds specifically and reversibly to a single class of sites in sarcolemmal membrane vesicles prepared from bovine aortic smooth muscle. These sites display a Kd of 100 pM for the iodinated toxin, as determined by either equilibrium or kinetic binding analyses. Binding site density is about 500 fmol/mg of protein in isolated membranes. The addition of low digitonin concentrations to disrupt the vesicle permeability barrier increases the maximum receptor concentration to 1.5 pmol/mg of protein, correlating with the observations that ChTX binds only at the external pore of PK,Ca and that the membrane preparation is of mixed polarity. Competition studies with ChTX yield a Ki of about 20 pM for native toxin. Binding of [125I]ChTX is modulated by ionic strength as well as by metal ions that are known to interact with PK,Ca. Moreover, tetraethylammonium ion, which blocks PK,Ca with moderately high affinity when applied at the external membrane surface, inhibits [125I]ChTX binding in an apparently competitive fashion with a Ki similar to that found for channel inhibition. In marked contrast, agents that do not inhibit PK,Ca in smooth muscle (e.g. tetrabutylammonium ion, other toxins homologous with ChTX, and pharmacological agents that modulate the activity of dissimilar ion channels) have no effect on [125I]ChTX binding in this tissue. Taken together, these results suggest that the binding sites for ChTX which are present in vascular smooth muscle are directly associated with PK,Ca, thus identifying [125I]ChTX as a useful probe for elucidating the biochemical properties of these channels.