CYP11B2 gene haplotypes independently and in concurrence with aldosterone and aldosterone to renin ratio increase the risk of hypertension

OBJECTIVES

Aldosterone synthase produces aldosterone, which regulates electrolytes and thereby blood pressure. Polymorphisms in aldosterone-synthase gene (CYP11B2) may associate with heterogeneous aldosterone production and hypertension. Hence, we investigated -344T/C, Iw/Ic polymorphisms of CYP11B2, plasma renin activity (PRA) and aldosterone concentration (PAC).

DESIGN AND METHODS

Consecutive ethnically-matched 450 hypertensive patients and 360 controls were screened by PCR-RFLP for genotypes and haplotypes; PRA and PAC were measured.

RESULTS

The Iw/Ic polymorphism distribution differed significantly between the two groups (LRT chi(2)=15.8, df=2, P=0.000). The mutant allele-Ic and genotype-Ic/Ic were overrepresented in patients (35% versus 27% and 13% versus 7%). Overrepresentation of T-Ic haplotype in patients was identified as risk haplotype (P=0.000). Patients had significantly higher PAC and aldosterone-to-renin ratio (ARR; P=0.000), which was Ic-allele dependent.

CONCLUSIONS

The haplotype T-Ic associated with hypertension susceptibility. Correlation between Ic-allele and raised ARR likely serve in hypertension management.

Whole body protection against lethal ionizing radiation in mice by REC-2001: a semi-purified fraction of Podophyllum hexandrum

The current study has concentrated on assessment of the radioprotective potential of REC-2001, a semi-purified fraction of rhizomes of Podophyllum hexandrum, in Swiss albino Strain 'A' mice exposed to 10 Gy whole-body gamma radiation. Animals were treated with 10 and 15 mg/kg b wt (i.p.) of REC-2001 1h prior to exposure to a lethal dose of gamma-radiation (10 Gy) and observed upto 30 days. For analysis of maximum tolerable dose (MTD), LD(50) and acute toxic dose, different concentrations of the extract were administered to animals and their mortality and morbidity status was observed upto 72 h and one week, respectively. Dose reduction factor (DRF) was determined by exposing REC-2001 pre-treated mice to supra-lethal doses of gamma-radiation. Endogenous spleen colony forming units (CFU), DNA strand breaks in thymocytes (alkaline halo assay) and lipid degradation was studied to understand the mechanism of radioprotection. A single dose of REC-2001 (10 and 15 mg/kg b wt i.p.) exhibited >90% survival in the pre-treated irradiated group versus no survival in radiation control group. Single doses of upto 75 mg/kg b wt (i.p.) did not cause any mortality (MTD) in mice. REC-2001, a dose of 90 mg/kg b wt, resulted in 50% mortality (LD(50)), while the LD(100) was 115 mg/kg b wt REC-2001 exhibited a DRF of 1.62. CFU counts in the REC-2001 treated group were found significantly high (5.33/spleen) as compared to controls. Exposure of thymocytes to 10 Gy radiation resulted in increased halo diameter (45+/-3 microm) in comparison to untreated controls (8+/-1 microm). REC-2001 administration (500 microg/ml) decreased the halo diameter to 15+/-2 microm. Radiation-induced lipid degradation was also inhibited by REC-2001. The present study has revealed that REC-2001 is a promising radioprotective fraction that can be effectively used against lethal doses of gamma-radiation after further investigations in higher animal models.

Multi-organ failure due to Mycobacterium tuberculosis and Aspergillus flavus infection after allogeneic bone marrow transplantation

Mycobacterium tuberculosis (MT) is a serious, but rare infectious complication after allogeneic bone marrow transplantation (BMT). We describe a case of fatal sepsis due to MT and Aspergillus flavus after allogeneic BMT for Aplastic Anemia. The diagnosis was made on bone marrow biopsy and asitic fluid culture. Broadspectrum antituberculous and Amphotericin B therapy was started immediately after diagnosis. The patient developed severe hypoxia and finally died of multi-organ failure. Rapid progression of mycobacterial infection as well as fungal infection should be considered in patients post BMT with unexplained fever, particularly in patients from endemic areas.

Port exteriorization appendectomy: is it the future?

The time honoured surgical procedure open appendectomy seems to be on the decline, it may be replaced in the modern era by laparoscopic appendectomy ("in appendectomy") performed with three trocars, or by the port exteriorization appendectomy ("out appendectomy") which can be done with two ports or even one. These techniques combine the benefits of decreased tissue trauma and operative time in addition to other advantages of minimal invasion. We conducted this study to know the effectiveness of Port Exteriorization Appendectomy, to analyze its complications and to assess the conversion rate. A one year prospective study consisted of fifty cases; a combination of emergency and elective group. They were operated under general anaesthesia and different variables were documented. Mean operative time, conversion rate, hospital stay, complications and patient satisfaction. There were 27 females with the (F: M) ratio of 1.17:1. The operative time of 23.3 mins, conversion in 4 (8.0%) patients and 2.4 days of hospital stay contributed to 86.0% operative success rate. Surgical site infection was seen in 5 (10.0%) patients and one (2.0%) developed pelvic abscess. On analysis of the satisfaction level, 44(93.6%) were completely satisfied and one (2.1%) patient seemed disappointed with the technique for cosmesis though, 42 (89.3%) remained completely satisfied and 5(10.7%) didn't like their scars. Port exteriorization appendectomy's efficacy can be verified by 86.0% success rate, operative time of 23.3 mins, indoor stay of 2.4 days, and minimal undesirable sequlae. However, more authentic results could be obtained if this technique is compared to open or laparoscopic appendectomy in a well designed randomized controlled clinical trial.

Protective efficacy of semi purified fraction of high altitude podophyllum hexandrum rhizomes in lethally irradiated Swiss albino mice

A fraction of high altitude Podophyllum hexandrum rhizome, REC-2006, was evaluated for its radioprotective efficacy against lethal gamma-irradiation (10 Gy, whole body) in Swiss albino mice. The maximum tolerated dose (MTD) and LD50 of this fraction were found to be 45 mg/kg b.w. and 74 mg/kg b.w. respectively. Pre-irradiation (- 2 h, ) administration (i.p.) of 6 or 8 mg/kg b.w. of REC-2006 rendered > 90% survival in lethally irradiated mice. The dose reduction factor was calculated to be 1.62 considering survival as the end point. REC-2006 treatment marked in significant increase in endogenous spleen colony forming units. In REC-2006 treated group, super oxide dismutase activity was increased significantly compared to the radiation control group (Liver, p = 0.00, Jejunum p = 0.00). The extract also inhibited radiation induced lipid peroxidation in liver (p = 0.00) at 24 h. REC-2006 administration (100-200 microg/ml) significantly reduced the halo diameter in mice thymocytes. Nearly 10 fold difference between the effective dose (6 mg/kg b.w.) and LD50 and the high degree of whole body survival (> 90% against 10 Gy irradiation) indicates REC-2006 to be safe and highly promising to achieve significant radioprotection against lethal radiation. Further purification and identification of active molecules and their efficacy studies in higher animals therefore demand attention.

Hydroxyurea in thalassemia intermedia—a promising therapy

Pharmacological agents such as hydroxyurea (HU) have been known to cause induction of fetal hemoglobin and possibly may alleviate the symptoms in thalassemia intermedia patients. Thirty-seven patients with beta-thalassemia intermedia were enrolled to assess response to HU therapy. Major response was defined as transfusion independence or hemoglobin rise of more than 20 g/l and minor response as rise in hemoglobin of 10-20 g/l or reduction in transfusion frequency by 50%. The median age was 10 years (range: 4-50 years) and median follow-up was 12 months (range: 4-36 months). Twenty-six patients (70.2%) showed response to HU therapy. Seventeen patients (45.9%) were major responders, and nine patients (24.3%) showed minor response. There was no correlation of response with beta-thalassemia mutation or XmnI polymorphism; however, the presence of alpha(3.7) deletion was associated with major response in three patients. Mean fetal hemoglobin (HbF) levels rose on HU therapy. Older age, low baseline F cell percent, and low baseline HbF levels (below 10%) were predictors of poor response. Response was evident within 1 month of starting HU therapy in the majority of responders. Thus, a short trial of HU therapy can predict durable response.

Clinical, haematological and histomorphological profile of adult myelodysplastic syndrome. Study of 96 cases in a single institute

Myelodysplastic syndromes (MDS) are clonal haematopoietic stem cell disorders characterised by ineffective and dyspoietic haematopoiesis. The natural history of these disorders is variable and ranges from a chronic to a rapid course towards leukaemic progression. Certain shortcomings have been encountered in the French-American-British (FAB) classification over the years, and therefore there is a need for an alternative method of classification. In 1999, the WHO published a revised classification of MDS. In the present study, we have analysed the clinical, haematological and histomorphological features in 96 cases of primary MDS seen in the department of haematology at the All India Institute of Medical Sciences (AIIMS) over a 6-yr period (1996-2001). Both FAB and WHO classifications have been incorporated and the Bournemouth scoring system applied in each case at presentation. The Bournemouth scoring system, in the absence of a cytogenetic study, offers a good prognostication and long-term survival estimate.

Paucibacillary tuberculosis in mice after prior aerosol immunization with Mycobacterium bovis BCG

To develop a murine model of paucibacillary tuberculosis for experimental chemotherapy of latent tuberculosis infection, mice were immunized with viable Mycobacterium bovis BCG by the aerosol or intravenous route and then challenged six weeks later with virulent Mycobacterium tuberculosis. The day after immunization, the counts were 3.71 +/- 0.10 log(10) CFU in the lungs of aerosol-immunized mice and 3.65 +/- 0.11 and 4.93 +/- 0.07 log(10) CFU in the lungs and spleens of intravenously immunized mice, respectively. Six weeks later, the lungs of all BCG-immunized mice had many gross lung lesions and splenomegaly; the counts were 5.97 +/- 0.14 and 3.54 +/- 0.07 log(10) CFU in the lungs and spleens of aerosol-immunized mice, respectively, and 4.36 +/- 0.28 and 5.12 +/- 0.23 log(10) CFU in the lungs and spleens of intravenously immunized mice, respectively. Mice were then aerosol challenged with M. tuberculosis by implanting 2.37 +/- 0.13 log(10) CFU in the lungs. Six weeks after challenge, M. tuberculosis had multiplied so that the counts were 6.41 +/- 0.27 and 4.44 +/- 0.14 log(10) CFU in the lungs and spleens of control mice, respectively. Multiplication of M. tuberculosis was greatly limited in BCG-immunized mice. Six weeks after challenge, the counts were 4.76 +/- 0.24 and 3.73 +/- 0.34 log(10) CFU in the lungs of intravenously immunized and aerosol-immunized mice, respectively. In contrast to intravenously immunized mice, there was no detectable dissemination to the spleen in aerosol-immunized mice. Therefore, immunization of mice with BCG by the aerosol route prior to challenge with a low dose of M. tuberculosis resulted in improved containment of infection and a stable paucibacillary infection. This model may prove to be useful for evaluation of new treatments for latent tuberculosis infection in humans.

Regulation of butyrate uptake in Caco-2 cells by phorbol 12-myristate 13-acetate

Butyrate and the other short-chain fatty acids (SCFAs) are the most abundant anions in the colonic lumen. Also, butyrate is the preferred energy source for colonocytes and has been shown to regulate colonic electrolyte and fluid absorption. Previous studies from our group have demonstrated that the HCO(3)(-)/SCFA(-) anion exchange process is one of the major mechanisms of butyrate transport across the purified human colonic apical membrane vesicles and the apical membrane of human colonic adenocarcinoma cell line Caco-2 and have suggested that it is mainly mediated via monocarboxylate transporter-1 (MCT-1) isoform. However, little is known regarding the regulation of SCFA transport by various hormones and signal transduction pathways. Therefore, the present studies were undertaken to examine whether hydrocortisone and phorbol 12-myristate 13-acetate (PMA) are involved in a possible regulation of the butyrate/anion exchange process in Caco-2 cells. The butyrate/anion exchange process was assessed by measuring a pH-driven [(14)C]butyrate uptake in Caco-2 cells. Our results demonstrated that 24-h incubation with PMA (1 microM) significantly increased [(14)C]butyrate uptake compared with incubation with 4alphaPMA (inactive form). In contrast, incubation with hydrocortisone had no significant effect on butyrate uptake in Caco-2 cells compared with vehicle (ethanol) alone. Induction of butyrate uptake by PMA appeared to be via an increase in the maximum velocity (V(max)) of the transport process with no significant changes in the K(m) of the transporter for butyrate. Parallel to the increase in the V(max) of [(14)C]butyrate uptake, the MCT-1 protein level was also increased in response to PMA incubation. Our studies demonstrated that the butyrate/anion exchange was increased in response to PMA treatment along with the induction in the level of MCT-1 expression in Caco-2 cells.

Subclassification of HbS syndrome: is it necessary?

Sickle beta-thalassaemia (S beta-thalassaemia) is a condition, which results from coinheritance of a sickle cell gene and a beta-thalassaemia gene. The clinical phenotype depends on the type of beta-thalassaemia gene (beta+ or beta(o)). There are several similarities in clinical and haematological features, which sometimes pose a difficulty in correct diagnosis. A definitive diagnosis is required in order to initiate early supportive treatment in patients with homozygous sickle cell disease (SS disease) and to define the later clinical course. Forty-seven cases of haemoglobin sickle syndrome (HbS syndrome) were studied. The clinico-haematological features and high-performance liquid chromatography (HPLC) results from 17 patients with S beta-thalassaemia were compared with those of SS disease (10 patients). Splenomegaly was more commonly found in patients with S beta-thalassaemia. Among the haematological features, red blood cell counts and HbA2 levels were significantly higher in patients with S beta-thalassaemia, while red cell indices, such as MCV, MCH were significantly lower than those seen SS disease. MCHC, PCV total haemoglobin (Hb), HbS, A and HbF were similar in the two groups.

Isolated extra-cranial internal carotid artery aneurysm in a young adult with Eale's disease

A young male patient, a known case of Eale's disease presented with a large isolated aneurysm of the extra-cranial part of internal carotid artery. Detailed investigation failed to establish the etiology of the aneurysm, and it is possible that the underlying pathology may be the same as that of Eale's disease. Eale's disease is an idiopathic vascular disease of the peripheral retina and we hypothesize that aneurysm in this patient may be associated with Eale's disease of the eye.

Endoluminal treatment of infrarenal abdominal aortic aneurysm with bifurcated stent-graft system

Atherosclerotic infrarenal aortic aneurysm has been traditionally treated by open surgical repair. We report a high risk case where the aneurysm was successfully treated by the new technique of endoluminal stent graft placement.

Mechanism of n-butyrate uptake in the human proximal colonic basolateral membranes

Current studies were undertaken to characterize the mechanism of short-chain fatty acid (SCFA) transport in isolated human proximal colonic basolateral membrane vesicles (BLMV) utilizing a rapid-filtration n-[(14)C]butyrate uptake technique. Human colonic tissues were obtained from mucosal scrapings from organ donor proximal colons. Our results, consistent with the existence of a HCO(3)(-)/SCFA exchanger in these membranes, are summarized as follows: 1) n-[(14)C]butyrate influx was significantly stimulated into the vesicles in the presence of an outwardly directed HCO(3)(-) and an inwardly directed pH gradient; 2) n-[(14)C]butyrate uptake was markedly inhibited (approximately 40%) by anion exchange inhibitor niflumic acid (1 mM), but SITS and DIDS (5 mM) had no effect; 3) structural analogs e.g., acetate and propionate, significantly inhibited uptake of HCO(3)(-) and pH-gradient-driven n-[(14)C]butyrate; 4) n-[(14)C]butyrate uptake was saturable with a K(m) for butyrate of 17.5 +/- 4.5 mM and a V(max) of 20.9 +/- 1.2 nmol x mg protein(-1) x 5 s(-1); 5) n-[(14)C]butyrate influx into the vesicles demonstrated a transstimulation phenomenon; and 6) intravesicular or extravesicular Cl(-) did not alter the anion-stimulated n-[(14)C]butyrate uptake. Our results indicate the presence of a carrier-mediated HCO(3)(-)/SCFA exchanger on the human colonic basolateral membrane, which appears to be distinct from the previously described anion exchangers in the membranes of colonic epithelia.

Encounters with pseudoaneurysms in orthopaedic practice

Thirteen pseudoaneurysms are presented of which five were caused as a complication of pin/wire placement of external fixators (one conventional and four Ilizarov frames). The most common symptom was the presence of profuse persistent bleeding from either the wound or the pin/wire site. In nine patients the pseudoaneurysm was directly caused by a fracture or subsequent fracture stabilisation. Pre-operative evaluation included radiography, arteriography, Doppler and computed tomography (CT) angiography. Depending on the site and size of the pseudoaneurysm management consisted of either ligation, resection and end-to-end anastamosis/vein grafting, lateral suture, endoaneurysmorrhaphy or selective embolisation.A high index of suspicion needs to be maintained following penetrating injury in the vicinity of a major vessel, particularly in the presence of persisting symptoms. External fixators are widely used to treat complex orthopaedic problems. The procedure is technically demanding, requiring a sound knowledge of cross-sectional limb anatomy. Injudicious use may result in potentially life/limb threatening complication of pseudoaneurysm.

The ORF3 protein of hepatitis E virus binds to Src homology 3 domains and activates MAPK

The hepatitis E virus (HEV) is the causative agent of hepatitis E, an acute form of viral hepatitis. The biology and pathogenesis of HEV remain poorly understood. We have used in vitro binding assays to show that the HEV ORF3 protein (pORF3) binds to a number of cellular signal transduction pathway proteins. This includes the protein tyrosine kinases Src, Hck, and Fyn, the p85alpha regulatory subunit of phosphatidylinositol 3-kinase, phospholipase Cgamma, and the adaptor protein Grb2. A yeast two-hybrid assay was used to further confirm the pORF3-Grb2 interaction. The binding involves a proline-rich region in pORF3 and the src homology 3 (SH3) domains in the cellular proteins. Competition assays and computer-assisted modeling was used to evaluate the binding surfaces and interaction energies of the pORF3.SH3 complex. In pORF3-expressing cells, pp60(src) was found to associate with an 80-kDa protein, but no activation of the Src kinase was observed in these cells. However, there was increased activity and nuclear localization of ERK in the pORF3-expressing cells. These studies suggest that pORF3 is a viral regulatory protein involved in the modulation of cell signaling. The ORF3 protein of HEV appears to be the first example of a SH3 domain-binding protein encoded by a virus that causes an acute and primarily self-limited infection.

Evidence for the existence of a distinct SO(4)(--)-OH(-) exchange mechanism in the human proximal colonic apical membrane vesicles and its possible role in chloride transport

Recent studies have demonstrated that mutations in human downregulated in adenoma gene (DRA) result in congenital chloride diarrhea (CLD), and that DRA may be involved in chloride transport across the intestinal apical domains. DRA is highly homologous to sulfate transporters, but not to any member of the anion exchanger gene family (AEs). Our previous studies have characterized the existence of a distinct Cl(-)-OH(-) (HCO(3)(-)) exchanger, with minimal affinity for sulfate in the human colonic apical membrane vesicles (AMV). However, the mechanism(s) of sulfate movement across the colonocyte plasma membranes in the human colon is not well understood. Current studies were undertaken to elucidate sulfate transport pathways in AMVs of human proximal colon. Purified AMV and rapid filtration (35)SO(4)(--) uptake techniques were used. Our results demonstrate the presence of a pH gradient-driven carrier-mediated SO(4)(--)-OH(-) exchange process in the human proximal colonic luminal membranes based on the following: a marked increase in the SO(4)(--) uptake in the presence of an outwardly directed OH(-) gradient; a significant inhibition of SO(4)(--) uptake by the membrane anion transport inhibitor, DIDS; demonstration of saturation kinetics (K(m) for SO(4)(--): 0.80 +/- 0.17 mM and Vmax 649 +/- 74 pmol/mg protein/10 sec); competitive inhibition of SO(4)(--)-OH(-) exchange by oxalate; SO(4)(--) uptake was insensitive to alterations in the membrane potential; and inwardly directed Na(+) gradient under non-pH gradient conditions did not stimulate SO(4)(--) uptake. SO(4)(--) uptake was significantly inhibited by increasing concentrations of chloride (1-10 mM) in the incubation media with a K(i) for Cl(-) of 9.3 +/- 1.4 mM. In contrast, OH(-)/HCO(3)(-) gradient-driven (36)Cl(-) uptake into these vesicles was unaffected by increasing concentrations of sulfate (10-50 mM). The above data indicate that two distinct transporters may be involved in SO(4)(--) and Cl(-) transport in the human intestinal apical membranes: an anion exchanger with high affinity for SO(4)(--) and oxalate but low affinity for Cl(-), and a distinct Cl(-)-OH(-) (HCO(3)(-)) exchanger with low affinity for SO(4)(--).

Differential regulation of the expression of Na(+)/H(+) exchanger isoform NHE3 by PKC-alpha in Caco-2 cells

Na(+)/H(+) exchange (NHE) activity has been shown to be regulated by various external signals and protein kinases in many tissues and cell types. A family of six NHE isoforms has been identified. Three isoforms, NHE1, NHE2, and NHE3, have been shown to be expressed in the human intestine. The present studies were designed to study regulation of these human NHE isoforms by the alpha-isoform of protein kinase C (PKC) in the Caco-2 cell line. The mRNA levels of the NHE isoforms in Caco-2 cells were initially measured by a semiquantitative RT-PCR technique in response to PKC downregulation by long-term exposure to 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA) for 24 h. PKC downregulation resulted in an approximately 60% increase in the mRNA level for NHE3, but not for NHE1 or NHE2. Utilizing dichlorobenzimidazole riboside, an agent to block the synthesis of new mRNA, we demonstrated that the increase in the NHE3 mRNA in response to downregulation of PKC was predominantly due to an increase in the rate of transcription, rather than a decrease in the NHE3 mRNA stability. Consistent with the mRNA results, our data showed that amiloride-sensitive (22)Na(+) uptake was increased after incubation of Caco-2 cells with 1 microM TPA for 24 h. To elucidate the role of PKC-alpha, an isoform downregulated by TPA, the relative abundance of NHE isoform mRNA levels and the apical NHE activity were assessed in Caco-2 cells over- and underexpressing PKC-alpha. Our results demonstrated that NHE3, but not NHE1 or NHE2, mRNA was downregulated by PKC-alpha and that apical NHE activity was higher in cells underexpressing PKC-alpha and lower in cells overexpressing PKC-alpha than in control cells. In conclusion, these data demonstrate a differential regulation of NHE3, but not NHE2 or NHE1, expression by PKC in Caco-2 cells, and this regulation appears to be predominantly due to PKC-alpha.

Detection of rifampin resistance in Mycobacterium tuberculosis in a single tube with molecular beacons

Current clinical assays for determining antibiotic susceptibility in Mycobacterium tuberculosis require many weeks to complete due to the slow growth of the bacilli. Here we demonstrate an extremely sensitive single-tube PCR assay that takes less than 3 h and reliably identifies rifampin-resistant M. tuberculosis in DNA extracted directly from sputum. Ninety-five percent of mutations associated with rifampin resistance occur in an 81-bp core region of the bacterial RNA polymerase gene, rpoB. All mutations that occur within this region result in rifampin resistance. The assay uses novel nucleic acid hybridization probes called molecular beacons. Five different probes are used in the same reaction, each perfectly complementary to a different target sequence within the rpoB gene of rifampin-susceptible bacilli and each labeled with a differently colored fluorophore. Together, their target sequences encompass the entire core region. The generation of all five fluorescent colors during PCR amplification indicates that rifampin-susceptible M. tuberculosis is present. The presence of any mutation in the core region prevents the binding of one of the molecular beacons, resulting in the absence of one of the five fluorescent colors. When 148 M. tuberculosis clinical isolates of known susceptibility to rifampin were tested, mutations associated with rifampin resistance were detected in 63 of the 65 rifampin-resistant isolates, and no mutations were found in any of the 83 rifampin-susceptible isolates. When DNA extracted directly from the sputum of 11 patients infected with rifampin-resistant tuberculosis was tested, mutations were detected in all of the samples. The use of this rapid assay should enable early detection and treatment of drug-resistant tuberculosis in clinical settings.

Mechanism of thiamine uptake by human jejunal brush-border membrane vesicles

Thiamine, a water-soluble vitamin, is essential for normal cellular functions, growth and development. Thiamine deficiency leads to significant clinical problems and occurs under a variety of conditions. To date, however, little is known about the mechanism of thiamine absorption in the native human small intestine. The objective of this study was, therefore, to characterize the mechanism of thiamine transport across the brush-border membrane (BBM) of human small intestine. With the use of purified BBM vesicles (BBMV) isolated from the jejunum of organ donors, thiamine uptake was found to be 1) independent of Na(+) but markedly stimulated by an outwardly directed H(+) gradient (pH 5.5(in)/pH 7.5(out)); 2) competitively inhibited by the cation transport inhibitor amiloride (inhibitor constant of 0.12 mM); 3) sensitive to temperature and osmolarity of the incubation medium; 4) significantly inhibited by thiamine structural analogs (amprolium, oxythiamine, and pyrithiamine), but not by unrelated organic cations (tetraethylammonium, N-methylnicotinamide, or choline); 5) not affected by the addition of ATP to the inside and outside of the BBMV; 6) potential insensitive; and 7) saturable as a function of thiamine concentration with an apparent Michaelis-Menten constant of 0.61 +/- 0.08 microM and a maximal velocity of 1.00 +/- 0.47 pmol. mg protein(-1). 10 s(-1). Carrier-mediated thiamine uptake was also found in BBMV of human ileum. These data demonstrate the existence of a Na(+)-independent, pH-dependent, amiloride-sensitive, electroneutral carrier-mediated mechanism for thiamine absorption in native human small intestinal BBMV.