Biomedical subjects

R W Wilson

Publications and source records attributed to R W Wilson.

At least 37 records · Page 2Linked to original sources

PubMed1999

Mycobacterium wolinskyi sp. nov. and Mycobacterium goodii sp. nov., two new rapidly growing species related to Mycobacterium smegmatis and associated with human wound infections: a cooperative study from the International Working Group on Mycobacterial Taxonomy.

Previous investigations demonstrated three taxonomic groups among 22 clinical isolates of Mycobacterium smegmatis. These studies were expanded to 71 clinical isolates, of which 35 (49%) (group 1) were identical to five ATCC reference strains including the type strain ATCC 19420T. Twenty-eight isolates (39%) were group 2, and eight isolates (11%) were group 3. Isolates of groups 2 and 3 were most often associated with post-traumatic or post-surgical wound infections including osteomyelitis, were susceptible to sulfamethoxazole, amikacin, imipenem and the tetracyclines, variably resistant to clarithromycin, and susceptible (group 1), intermediately resistant (group 2) or resistant (group 3) to tobramycin. The three groups were similar by routine biochemical and growth characteristics, but had different mycolic acid dimethoxy-4-coumarinylmethyl ester elution patterns by HPLC and different PCR-restriction enzyme patterns of a 439 bp fragment of the hsp-65 gene. Group 3 isolates differed from group 1 by 18 bp by 16S rRNA sequencing and exhibited < 25% homology by DNA-DNA hybridization, being most closely related to Mycobacterium mageritense. The 16S rRNA of group 1 and group 2 isolates differed by only 3 bp, but by DNA-DNA hybridization they exhibited only 40% homology. The following names are proposed: Mycobacterium goodii sp. nov. for group 2 isolates (type strain ATCC 700504T = MO69T), Mycobacterium wolinskyi sp. nov. for group 3 isolates (type strain ATCC 700010T = MO739T) and Mycobacterium smegmatis sensu stricto for group 1 isolates.

Adolescent↗

PubMed1999

Evidence from molecular fingerprinting of limited spread of drug-resistant tuberculosis in Texas.

To determine the contribution of recent transmission to spread of drug-resistant tuberculosis in Texas, we performed IS6110-based and pTBN12-based restriction fragment length polymorphism (RFLP) analyses on Mycobacterium tuberculosis isolates. Isolates collected from 201 patients in Texas between 1992 and 1994 were studied. The distribution of cases was strikingly focal. All cases were reported from 35 of the 254 counties in Texas, and 74% (148 of 201) were reported from only 9 counties. One hundred sixty-one (80%) of the patients had M. tuberculosis isolates with unique RFLP patterns, and 41 (20%) patients were in 20 clusters, each comprising 2 to 3 patients. The largest number of cases of drug-resistant tuberculosis were reported in counties bordering Mexico, but the percentage of clustered cases was highest in northeast Texas and in counties that included the cities of Dallas, Fort Worth, and Houston. Compared to nonclustered patients, clustered patients were more likely to be African American and to have been born in the United States. Clustered patients were significantly more likely to be from the same geographic area, and clustered patients from the same geographic area were more likely to have isolates with identical drug susceptibility patterns, suggesting that they were linked by recent transmission. In 11 of 20 clusters, clustered patients were from geographically separate regions, and most isolates did not have identical drug susceptibility patterns, suggesting that tuberculosis was contracted from a common source in the remote past. Based on the low percentage of clustered cases and the small cluster size, we conclude that there is no evidence for the extensive transmission of drug-resistant tuberculosis in Texas.

Adolescent↗

PubMed1999

Desmoid tumors of the pleura: a clinicopathologic mimic of localized fibrous tumor.

Intrathoracic desmoid tumors of the pleura are unusual tumors that are often clinically and histologically confused with localized fibrous tumor of the pleura or benign neurogenic tumors. We studied four cases of intrathoracic desmoid tumor of the pleura and reviewed the clinical, histopathologic, and immunohistochemical features of the four patients. Two men and two women, ranging in age from 16 to 66 years (mean, 44 yr) comprised the study group. Three patients presented with chest pain and one with shortness of breath. Two patients had a history of associated trauma in the area of the tumor. Three of the lesions were based in the parietal pleura and one in the visceral pleura. Treatment included complete resection (two cases), subtotal resection (one case), and subtotal resection followed by radiation therapy and complete resection (one case). The mean tumor size was 12.5 cm, and all of the tumors exhibited a bosselated, firm, white, cut surface. The histologic features of intrathoracic desmoid tumors were similar to those of desmoid tumors at more conventional sites. Infiltration of the adjacent fat and skeletal muscle was invariably present. The tumor cells were immunoreactive for vimentin, desmin, smooth muscle actin, and muscle-specific actin in three of the four cases and were negative for S-100 protein. Follow-up to date shows stable residual disease at 12 months (one case) and two patients with no evidence of disease at 12 and 96 months, respectively. Intrathoracic desmoid tumors often exhibit clinical and radiographic features similar to localized fibrous tumor of the pleura. They generally have histologic and behavioral characteristics identical to those of desmoid tumors at conventional sites. Like desmoid tumors elsewhere, complete resection with negative margins is vital to prevent local recurrence. Desmoid tumor should be considered in the differential of localized fibrous tumor of the pleura.

Adolescent↗

PubMed1998

The demand for prehospital emergency services in an aging society.

This research examines the implications of an aging society on the demand for prehospital emergency medical services (EMS). Using a large comprehensive set of population-based EMS utilization data (N = 73874) and population data from the 1990 Census for the City of Dallas, Texas, rates of utilization for eight age groups were computed for total EMS incidents, incidents requiring transport services, and a sub-category of transport services for individuals requiring services for life-threatening conditions. The pattern of utilization associated with age was found to be tri-modal with rates rising geometrically with age for individuals aged 65 and over. Compared to the age group 45 to 64 years of age, rates of utilization for those aged 85 years and older were 3.4 times higher (P < 0.001) for total EMS incidents, 4.5 times higher (P < 0.001) for emergency transports and 5.2 times higher (P < 0.001) for incidents of a life-threatening nature. A broad categorization of all EMS incidents by reason for requiring services indicates that the observed age-associated increase in utilization is due primarily to medical conditions rather than incidents arising from trauma. Finally, gender and racial/ethnic differences in utilization are briefly considered.

Adolescent↗

PubMed1998

Primary ependymoma of the mediastinum: a clinicopathologic study of three cases.

Primary mediastinal ependymomas are unusual tumors, with only two case reports previously reported in the literature. In this study, we review our experience with three cases of primary mediastinal ependymomas, including the clinical, histopathologic, immunohistochemical, and ultrastructural features. The three patients in this study were white women with a mean age of 50 years (age range, 36 to 71 years). Presenting symptoms were nonspecific; radiographically, all lesions were circumscribed posterior mediastinal masses without evidence of bone involvement. There was no evidence of central nervous system, sacral, or pelvic ependymoma. All tumors were completely resected, ranged in size from 5 to 7 cm (mean, 6 cm), and exhibited glistening pseudocapsules. Two tumors had a solid, tan-gray cut surface and one lesion was cystic with a mural tumor nodule. All neoplasms showed histologic features of conventional cellular ependymomas with perivascular pseudorosettes and occasional true ependymal rosettes. Germ cell components were not present in any case and immunohistochemical analysis showed glial fibrillary acidic protein, S-100, and patchy cytokeratin immunoreactivity in all three cases as well as absence of reactivity for HMB 45, chromogranin, and synaptophysin. Ultrastructural features included multipart "zipper-like" junctions, intracytoplasmic lumina containing microvilli, occasional cytoplasmic basal bodies, and apical cilia. A microscopic metastasis was present in a regional lymph node in one case at the time of resection; however, there is no evidence of recurrence or distant metastasis in any of the cases during the postoperative period (mean length of follow-up, 64 months). Ependymomas rarely occur in the mediastinum and have a predilection for the posterior mediastinum. The paravertebral location, microscopic identification of adjacent sympathetic ganglia, and lack of teratomatous or other germ cell components suggest that mediastinal ependymomas are likely derived from paravertebral ependymal rests. Primary mediastinal ependymomas are characterized by a prolonged and indolent clinical course. Metastasis to regional lymph nodes may occur, but distant metastases are unusual in our experience. Complete surgical excision seems to offer the best chance for long-term survival.

Adult↗

PubMed1998

Pathological-radiological correlations: pathological and radiological correlation of endobronchial neoplasms: part II, malignant tumors.

The majority of lung neoplasms are malignant. Many of these are central and have an associated endobronchial component. Most such neoplasms are of surface epithelial origin; however, neoplasms of submucosal gland, mesenchymal, and lymphoreticular origin may also demonstrate an endobronchial component. Because of their endobronchial location and associated symptoms, these patients often present at an earlier stage than purely parenchymal lung malignancies. The radiographic features in such cases may be similar to those associated with benign endobronchial tumors; however, there are certain radiological signs that are more suggestive of a malignant process. Despite these circumstances, conservative management such as endoscopic excision are inappropriate in most instances. The clinicopathologic and radiological features of these lesions are detailed.

Bronchial Neoplasms↗

PubMed1998

Clinical application of PCR-restriction enzyme pattern analysis for rapid identification of aerobic actinomycete isolates.

The accuracy and practicality of PCR-restriction enzyme pattern analysis (PRA) for routine identification of aerobic actinomycete clinical isolates were evaluated for 299 cultures submitted to the Mycobacteria/Nocardia Laboratory at the University of Texas Health Center at Tyler. PRA identification using an amplified 439-bp segment (amplicon) of the 65-kDa heat shock protein gene was compared to identification by traditional methods, including growth characteristics, susceptibility patterns, biochemical testing, and high-performance liquid chromatography analysis. Microbiological examination of six cultures ruled out aerobic actinomycetes, and they were omitted from the study. Amplicons were analyzed with BstEII, HaeIII, MspI, HinfI, and BsaHI. When necessary, AciI, HhaI, and NarI were also used. From March 1995 through May 1997 (27 months), 274 of the remaining 293 (93.5%) isolates were accurately identified by PRA. Major diagnostic groups included 170 mycobacteria, 93 nocardiae, and 30 other aerobic actinomycetes. Mixed cultures were readily recognized by PRA, including a wound culture that contained two Nocardia taxa that were indistinguishable morphologically. Mycobacterium mucogenicum was identified in three cultures heavily contaminated with gram-positive cocci. The 19 isolates that produced PRA patterns that did not match those in the current PRA database were differentiated into 8 Mycobacterium species and 11 other aerobic actinomycetes by the presence or absence of BstEII recognition sites. Identification of 15 of these 19 isolates was also equivocal by traditional methods. PRA results were reportable within 2 to 5 working days and were as accurate as and faster and less expensive to obtain than those of traditional methods.

Actinomycetales↗

PubMed1998

Potassium permeability in the absence of fluid reabsorption in proximal tubule of the anesthetized rat.

A luminal microperfusion technique was used to examine the K+ permeability of surface proximal convoluted tubules (PCT) in the kidney of anesthetized rats. Transtubular potassium concentration ([K+]) gradients were varied by altering the concentration of KCl in luminal perfusates, to which 32 mmol/l of the impermeant solute raffinose was also added to prevent net fluid reabsorption. The arithmetic mean transtubular [K+] gradient was highly predictive of net potassium flux, yielding an apparent K+ permeability of 31.9 +/- 1.7 x 10(-5) cm/s in the absence of fluid reabsorption. When compared using identical calculation techniques, we found this was not significantly different from the permeability derived in a previous study when fluid reabsorption was present [J. D. Kibble, M. Wareing, R. W. Wilson, and R.Green. Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 27): F778-F783, 1995]. We conclude that fluid reabsorption does not affect the apparent permeability of the proximal tubule to potassium. The apparent permeability to 86Rb, measured following its addition to luminal perfusates, was not significantly different from the value obtained for K+, suggesting that rubidium is a useful marker for net potassium movements in the PCT of the rat.

Absorption↗

PubMed1998

Telephone coverage and measurement of health risk indicators: data from the National Health Interview Survey.

OBJECTIVES: This study compared health behavior variables for all US households and households with telephones to measure the potential impact of telephone coverage on estimates from telephone surveys. METHODS: Data were derived from the 1991 through 1994 version of the National Health Interview Survey. RESULTS: Ninety-five percent of respondents lived in households with telephones. Differences in health indicators were small (< 1%) in comparisons between all households and those with telephones. Results were similar when only respondents below the poverty level were included. CONCLUSIONS: Telephone noncoverage effects appear to be small, supporting the use of telephone surveys for health risk behavior surveillance with most population groups.

Adult↗

PubMed1998

Reliability and responsiveness of disablement measures following acute ankle sprains among athletes.

The minimum amount of change which represents clinical improvement following ankle sprains is unknown. This study considers the usefulness of physiological and behavioral measures commonly employed for this purpose in sports rehabilitation settings. Thirteen collegiate athletes of both genders were measured at approximately 3 and 10 days post-grade I or II ankle sprain. Volumetric displacement and sagittal plane ankle range of motion measures were used as impairment indicators. Motor ability scores (activity count) and a perceived athletic ability measure (visual analog scale) were used to indicate functional limitations. Volumetric displacement and both functional limitation measures demonstrated responsiveness to change between two occasions of measurement separated by 1 week. Observed changes in range of motion deficits could not be distinguished from measurement error. The results of this study suggest that behavioral measures of motor activity and perceived athletic ability may be at least as useful as physical measures of organic dysfunction for assessing clinical improvement following acute ankle sprains among athletes.

Acute Disease↗

PubMed1997

The role of active transport in potassium reabsorption in the proximal convoluted tubule of the anaesthetized rat.

1. We have previously assessed the contributions of diffusion and convection to net potassium reabsorption in the rat proximal convoluted tubule (PCT). The present study was conducted to evaluate the role of active transport in convective potassium reabsorption by measuring the transepithelial potassium reflection coefficient (sigmaK) in the presence and absence of cyanide in anaesthetized rats previously prepared for in vivo microperfusion. 2. Osmotic water permeability (Pf) was measured in double-perfused tubules (lumen and peritubular capillaries) by manipulating the applied transepithelial osmotic gradient between -30 and +40 mosmol (kg H2O)(-1) using raffinose added to or subtracted from luminal perfusates. Pf was unaffected by the presence of cyanide when the estimated dissipation of osmotic gradients along each tubule were taken into account. 3. The proportion of K+ (and Na+) convectively transported with water fluxes (i.e. sigmaK) was not affected by cyanide. In the absence of active transport and following correction for any diffusive component, sigmaK was 0.56 +/- 0.13, indicating substantial solvent drag which probably occurs via the paracellular pathway. 4. However, cyanide caused a reduction in net potassium flux over the entire range of fluid fluxes used in double-perfusion experiments. Subsequent single-perfusion experiments (tubule lumen only) using the specific K+-H+-ATPase inhibitor, SCH28080, failed to reveal any direct evidence for a primary active K+ transporting mechanism involved in K+ reabsorption in the PCT.

Absorption↗

PubMed1997

Negative mood and urban versus rural residence: using proximity to metropolitan statistical areas as an alternative measure of residence.

The purposes of this report is to describe the distribution of reported negative mood by place of residence focusing on proximity to metropolitan statistical areas (MSA's) as an alternative to the traditional urban versus rural residence variable using the 1991 National Health Interview Survey's Health Promotion and Disease Prevention (NHIS-HPDP) supplement. The self-report of negative mood comes from the negative affect items of the Bradburn Affect Balance Scale categorized as high and low presence. The proximity to MSA's is a county-based measure developed as a combination of the MSA/non-MSA residence variable from the NHIS-HPDP and the United States Department of Agriculture (USDA) adjacency code from the Area Resource File (ARF). The proximity to MSA's measure has four categories: 1. MSA central city 2. MSA not central city 3. non-MSA adjacent (contiguous) to MSA 4. non-MSA not adjacent to MSA The odds ratios for negative mood were 1.24 (95 percent confidence limits [CL] = 1.11,1.38) for MSA central city and 1.26 (95 percent CL = 1.05,1.52) for non-MSA not adjacent to MSA as compared with MSA not central city. The odds ratio for non-MSA adjacent to MSA was not significantly different from MSA not central city. Data are presented by age, sex, race, and education. Thus, the proximity measure demonstrated greater discrimination in rates of negative mood than did urban versus rural or other measures of place of residence.

Adult↗

PubMed1997

Epithelial-myoepithelial carcinoma of the lung: immunohistochemical and ultrastructural observations and review of the literature.

Epithelial-myoepithelial carcinoma is a rare low-grade malignant salivary gland neoplasm that most commonly occurs in the parotid gland but can also arise in minor salivary glands. We report a case of a primary epithelial-myoepithelial carcinoma of the lung. The patient is a 55-year-old black woman who presented with increasing shortness of breath and productive cough of at least 3 months duration. A left lower lobe endobronchial lesion was identified radiographically. Surgical resection of the lesion was performed, obtaining a circumscribed, nonencapsulated 3.9 cm tan mass which was attached to the inner wall of the lateral basal segment bronchus. A biphasic proliferation of epithelial (cytokeratin positive; S-100 protein and muscle-specific actin negative) and myoepithelial (S-100 protein and muscle-specific actin positive with focal weak cytokeratin positive) cells was identified by immunohistochemical and ultrastructural analysis of formalin-fixed tissue. The patient is disease free 7 months after resection. Pulmonary epithelial-myoepithelial carcinoma likely derives from the submucosal bronchial glands and should be added to the growing list of salivary gland-type neoplasms that may occur as primary pulmonary neoplasms. Because its histology is identical to salivary epithelial-myoepithelial carcinoma, pulmonary epithelial-myoepithelial carcinoma should be considered a low-grade malignant neoplasm and should be designated as epithelial-myoepithelial carcinoma is preference to other terms that may not convey its malignant potential. Although follow-up on reported cases is limited, lobectomy with negative bronchial margin should be curative.

Carcinoma↗

PubMed1997

Pathological and radiological correlation of endobronchial neoplasms: Part I, Benign tumors.

Benign endobronchial lung neoplasms are extremely rare. Most such neoplasms are of mesenchymal origin; however, neoplasms of submucosal gland origin and surface epithelial origin also occur. The symptomatology and radiographic features of these tumors are often indistinguishable from those of malignant lung tumors. However, recognition and early diagnosis of these lesions may allow for conservative treatment and excellent patient outcome. The clinicopathologic and radiological features of these pulmonary neoplasms are discussed.

Bronchi↗

PubMed1997

Primary melanoma of the lung: a clinicopathologic and immunohistochemical study of eight cases.

Primary malignant melanoma of the lung (PMML) is an uncommon neoplasm that may be confused with more conventional types of lung cancer. Although the previously proposed criteria for diagnosis, including the presence of an in situ component, are often difficult to satisfy, this lesion is characterized by a poor prognosis, ultimately leading to patient death. We report eight cases of PMML that presented as solitary, central endobronchial neoplasms, resulting in a picture that closely resembled carcinoid tumor or poorly differentiated non-small-cell carcinoma of the lung. The mean age at diagnosis was 51 years (range 45-71). The patients included one woman and seven men. The histologic growth pattern varied from organoid to fascicular and included epithelioid to spindled cells with hyperchromatic to vesicular nuclei, prominent eosinophilic nucleoli, and abundant eosinophilic to clear cytoplasm with occasional intranuclear cytoplasmic inclusions. A bronchial in situ component was present in four cases. Initial interpretations included carcinoid tumor, non-small-cell carcinoma, and malignant melanoma. Melanin was present in all neoplasms on hematoxylin and eosin staining, although very focally in one case, and was Fontana-Masson positive in all cases. Immunohistochemically, diffuse strong positivity for S-100, HMB-45, and vimentin was present in all seven tumors tested. All seven tumors were negative for cytokeratin, CAM 5.2, and chromogranin. Ultrastructural examination of the eighth case showed dysmorphic premelanosomes but no neurosecretory granules. None of the patients had disseminated disease at presentation, and all patients underwent surgical resection (seven lobectomies and one excision). In this series, primary malignant melanoma of the lung was characterized by an aggressive postoperative course, with five patients dying of metastatic disease from 4 to 32 months after resection (median 14 months). Two patients are alive with metastatic disease at 4 and 30 months after surgery, and the eighth patient is alive with no evidence of disease 108 months after surgery at last follow-up. Metastatic melanoma was identified in various sites, including the lungs, adrenal glands, liver, mesentery, brain, and bone. The cases herein presented indicate that PMML should be included in the differential diagnosis of primary bronchial tumors.

Aged↗

PubMed1997

Rapid identification of clinically significant species and taxa of aerobic actinomycetes, including Actinomadura, Gordona, Nocardia, Rhodococcus, Streptomyces, and Tsukamurella isolates, by DNA amplification and restriction endonuclease analysis.

A previously described PCR-restriction fragment length polymorphism (RFLP) identification schema for Nocardia that used an amplified 439-bp segment (amplicon) of the 65-kDa heat shock protein gene was evaluated for potential use with isolates of all clinically significant aerobic actinomycetes. The study included 28 reference (American Type Culture Collection) strains and 198 clinical isolates belonging to 20 taxonomic groups. Of these 198 isolates, 188 could be differentiated by this PCR-RFLP method. Amplicons from all aerobic actinomycete isolates lacked BstEII recognition sites, thereby distinguishing them from those of mycobacteria that contain one or more such sites. Of 29 restriction endonucleases, MspI plus HinfI produced RFLP patterns that differentiated 16 of the 20 taxa. A single RFLP pattern was observed for 15 of 20 taxa that included 65% of phenotypically clustered isolates. Multiple patterns were seen with Gordona bronchialis, Nocardia asteroides complex type VI, Nocardia otitidiscaviarum, Nocardia transvalensis, and Streptomyces spp. Streptomyces RFLP patterns were the most heterogeneous (five patterns among 19 isolates), but exhibited a unique HinfI fragment of > 320 bp. RFLP patterns that matched those from type strains of Streptomyces albus, Streptomyces griseus, or Streptomyces somaliensis were obtained from 14 of 19 Streptomyces isolates. Only 10 of 28 isolates of N. otitidiscaviarum failed to yield satisfactory amplicons, while only 6 of 188 (3.2%) clinical isolates exhibited patterns that failed to match one of the 21 defined RFLP patterns. These studies extended the feasibility of using PCR-RFLP analysis as a rapid method for the identification of all clinically significant species and taxa of aerobic actinomycetes.

Actinomyces↗

PubMed1997

Recognition of a Nocardia transvalensis complex by resistance to aminoglycosides, including amikacin, and PCR-restriction fragment length polymorphism analysis.

Amikacin resistance, rare among nocardiae, was observed in 58 clinical isolates of nocardiae. All of these isolates hydrolyzed hypoxanthine, and 75 to 100% utilized citrate, D-galactose, and D-trehalose as sole carbon sources. Based on utilization of I-erythritol, D-glucitol, i-myo-inositol, D-mannitol, and ribitol and susceptibility to amoxicillin-clavulanic acid, the 58 isolates were separable into four groups. One group was negative for I-erythritol and ribitol and included all the isolates belonging to Nocardia asteroides complex antibiogram type IV. The remaining three groups were positive for I-erythritol and ribitol and were grouped within Nocardia transvalensis. The group that included the type strain was designated N. transvalensis sensu stricto, and the other two groups were designated new taxons 1 and 2. PCR-restriction fragment length polymorphism (RFLP) analysis of a 439-bp segment of the 65-kDa heat shock protein gene with XhoI and HinfI produced identical patterns for 53 (91%) and 58 (100%) isolates, respectively, and differentiated them from all other Nocardia taxa. NarI- and HaeIII-derived RFLP patterns clearly differentiated each of the four biochemically defined taxa. These four groups were also distinguishable by using the chromogenic substrates in Dade MicroScan test panels. By high-performance liquid chromatography, these isolates exhibited the same unique mycolic acid-ester elution patterns that differed from those of all other clinically significant nocardiae. Gas-liquid chromatographic analysis of fatty acids also produced similar patterns for all isolates that distinguished them from all other Nocardia taxa, but did not differentiate the four taxa within the complex. We propose the designation N. transvalensis complex for these four groups of nocardiae, pending further genetic evaluation.

Amikacin↗

PubMed1996

Bicarbonate secretion in interlobular ducts from guinea-pig pancreas.

1. The transport of HCO3- across the luminal membrane of pancreatic duct cells was studied by monitoring the luminal pH of isolated guinea-pig interlobular ducts after microinjection of an extracellular fluoroprobe, the dextran conjugate of 2'7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF-dextran). Luminal Cl- concentration was also measured by microfluorometry following microinjection of the dextran conjugates of 6-methoxy-N-(4-aminoalkyl)quinolinium bromide (ABQ-dextran) and Cl-NERF (Cl-NERF-dextran). 2. When HCO3-/CO2 was admitted to the bath, a transient acidification of the duct lumen was observed, followed by a marked alkalinization. The latter was abolished when the luminal Cl- concentration was reduced to 25-35 mM by replacement with glucuronate and may, therefore, be attributed to Cl(-)-HCO3- exchange at the luminal membrane. 3. Secretin, forskolin and acetylcholine stimulated HCO3- secretion into the lumen even when the luminal Cl- concentration was reduced to approximately 7 mM. Furthermore, agonist-evoked HCO3- secretion was not inhibited by luminal glibenclamide, dihydro-4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (H2DIDS) or 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB). These observations are not easily reconciled with HCO3- transport across the luminal membrane being mediated by Cl(-)-HCO3- exchange in parallel with a Cl- conductance. 4. Agonist-stimulated HCO3- secretion was blocked by omitting Na+ from the bath but not by addition of N-methyl-N-isobutylamiloride (MIA) or bafilomycin A1. This supports our previous conclusion that HCO3- entry into duct cells from the extracellular fluid requires Na+ but is not dependent on Na(+)-H+ exchange or vacuolar-type H(+)-ATPase activity. 5. The three actions of secretin on guinea-pig pancreatic duct cells described in this and the accompanying paper - stimulation of a relatively Cl(-)-insensitive luminal HCO3- efflux pathway, stimulation of basolateral Na(+)-HCO3- cotransport, and lack of effect on intracellular pH- require the current model of pancreatic HCO3- secretion to be modified.

Animals↗