Lessons Learned and Future Directions of MetaTutor: Leveraging Multichannel Data to Scaffold Self-Regulated Learning With an Intelligent Tutoring System

Self-regulated learning (SRL) is critical for learning across tasks, domains, and contexts. Despite its importance, research shows that not all learners are equally skilled at accurately and dynamically monitoring and regulating their self-regulatory processes. Therefore, learning technologies, such as intelligent tutoring systems (ITSs), have been designed to measure and foster SRL. This paper presents an overview of over 10 years of research on SRL with MetaTutor, a hypermedia-based ITS designed to scaffold college students' SRL while they learn about the human circulatory system. MetaTutor's architecture and instructional features are designed based on models of SRL, empirical evidence on human and computerized tutoring principles of multimedia learning, Artificial Intelligence (AI) in educational systems for metacognition and SRL, and research on SRL from our team and that of other researchers. We present MetaTutor followed by a synthesis of key research findings on the effectiveness of various versions of the system (e.g., adaptive scaffolding vs. no scaffolding of self-regulatory behavior) on learning outcomes. First, we focus on findings from self-reports, learning outcomes, and multimodal data (e.g., log files, eye tracking, facial expressions of emotion, screen recordings) and their contributions to our understanding of SRL with an ITS. Second, we elaborate on the role of embedded pedagogical agents (PAs) as external regulators designed to scaffold learners' cognitive and metacognitive SRL strategy use. Third, we highlight and elaborate on the contributions of multimodal data in measuring and understanding the role of cognitive, affective, metacognitive, and motivational (CAMM) processes. Additionally, we unpack some of the challenges these data pose for designing real-time instructional interventions that scaffold SRL. Fourth, we present existing theoretical, methodological, and analytical challenges and briefly discuss lessons learned and open challenges.

Tracking Changes in Students' Online Self-Regulated Learning Behaviors and Achievement Goals Using Trace Clustering and Process Mining

Success in online and blended courses requires engaging in self-regulated learning (SRL), especially for challenging STEM disciplines, such as physics. This involves students planning how they will navigate course assignments and activities, setting goals for completion, monitoring their progress and content understanding, and reflecting on how they completed each assignment. Based on Winne & Hadwin’s COPES model, SRL is a series of events that temporally unfold during learning, impacted by changing internal and external factors, such as goal orientation and content difficulty. Thus, as goal orientation and content difficulty change throughout a course, so might students’ use of SRL processes. This paper studies how students’ SRL behavior and achievement goal orientation change over time in a large (N = 250) college introductory level physics course taught online. Students’ achievement goal orientation was measured by repeated administration of the achievement goals questionnaire-revised (AGQ-R). Students’ SRL behavior was measured by analyzing their clickstream event traces interacting with online learning modules via a combination of trace clustering and process mining. Event traces were first divided into groups similar in nature using agglomerative clustering, with similarity between traces determined based on a set of derived characteristics most reflective of students’ SRL processes. We then generated causal nets for each cluster of traces via process mining and interpreted the underlying behavior and strategy of each causal net according to the COPES SRL framework. We then measured the frequency at which students adopted each causal net and assessed whether the adoption of different causal nets was associated with responses to the AGQ-R. By repeating the analysis for three sets of online learning modules assigned at the beginning, middle, and end of the semester, we examined how the frequency of each causal net changed over time, and how the change correlated with changes to the AGQ-R responses. Results have implications for measuring the temporal nature of SRL during online learning, as well as the factors impacting the use of SRL processes in an online physics course. Results also provide guidance for developing online instructional materials that foster effective SRL for students with different motivational profiles.

Multimodal Protocol for Assessing Metacognition and Self-Regulation in Adults with Learning Difficulties

Learning disabilities (LDs) encompass disorders of those who have difficulty learning and using academic skills, exhibiting performance below expectations for their chronological age in the areas of reading, writing, and/or mathematics. Each of the disorders making up the LDs involve different deficits; however, some commonalities can be found within that heterogeneity, such in terms of learning self-regulation and metacognition. Unlike in early ages and later educational levels, there are hardly any evidence-based evaluation protocols for adults with LDs. LDs influence academic performance but also have serious consequences in professional, social, and family contexts. In response to this, the current work proposes a multimodal evaluation protocol focused on metacognitive, self-regulation of learning, and emotional processes, which make up the basis of the difficulties in adults with LDs. The assessment is carried out through analysis of the on-line learning process using a variety methods, techniques, and sensors (e.g., eye tracking, facial expressions of emotion, physiological responses, concurrent verbalizations, log files, screen recordings of human-machine interactions) and off-line methods (e.g., questionnaires, interviews, and self-report measures). This theoretically-driven and empirically-based guideline aims to provide an accurate assessment of LDs in adulthood in order to design effective prevention and intervention proposals.

Multiple Negative Emotions During Learning With Digital Learning Environments - Evidence on Their Detrimental Effect on Learning From Two Methodological Approaches

Emotions are a core factor of learning. Studies have shown that multiple emotions are co-experienced during learning and have a significant impact on learning outcomes. The present study investigated the importance of multiple, co-occurring emotions during learning about human biology with MetaTutor, a hypermedia-based tutoring system. Person-centered as well as variable-centered approaches of cluster analyses were used to identify emotion clusters. The person-centered clustering analyses indicated three emotion profiles: a positive, negative and neutral profile. Students with a negative profile learned less than those with other profiles and also reported less usage of emotion regulation strategies. Emotion patterns identified through spectral co-clustering confirmed these results. Throughout the learning activity, emotions built a stable correlational structure of a positive, a negative, a neutral and a boredom emotion pattern. Positive emotion pattern scores before the learning activity and negative emotion pattern scores during the learning activity predicted learning, but not consistently. These results reveal the importance of negative emotions during learning with MetaTutor. Potential moderating factors and implications for the design and development of educational interventions that target emotions and emotion regulation with digital learning environments are discussed.

Application of enzymatically stable dipeptides for enhancement of intestinal permeability. Synthesis and in vitro evaluation of dipeptide-coupled compounds

Transport across the intestinal barrier of compounds with low permeability may be facilitated by targeting the human oligopeptide transporter, hPepT1. A flexible synthetic pathway for attaching compounds to dipeptides through ester or amide bonds was developed. Furthermore, a synthetic approach to functionalize model drugs from one key intermediate was generated and applied to a glucose-6-phosphatase active model drug. The model drug was coupled to D-Glu-Ala through various linkers, and the G-6-Pase activity as well as the aqueous solubility and transport properties of these prodrugs, as compared to those of the parent drugs, were examined. None of the peptide-coupled compounds seemed to be transported by hPepT1, though one of the peptide-coupled compounds had affinity for hPepT1. Interestingly, in one case the parent drug was actively effluxed, while the corresponding peptide-coupled prodrug was not. The low aqueous solubility of the parent compounds was not increased after attachment to a dipeptide. This suggests that only compounds with a certain intrinsic aqueous solubility should be targeted to hPepT1 by attachment to a dipeptide. Important information about the design of peptide-coupled drugs targeted for hPepT1 is presented.

Realism of confidence in obsessive-compulsive checkers

The study examined whether obsessive-compulsive (OC) checkers have reduced confidence in their knowledge. OC checkers were compared with panic disorder (PD) patients and nonpatient controls using a calibration-of-knowledge procedure. Participants completed a general knowledge questionnaire, rated their confidence in each answer, and estimated the total number of correct answers. These responses were converted to 2 measures of confidence relative to performance--over/underconfidence and over/underestimation. OC checkers had lower scores than nonpatients did on both measures, whereas the PD patients did not differ from either group. For the OC checkers, relative confidence was inversely related to the severity of obsessions. The authors speculate that confidence may depend on a confirmation bias in testing hypotheses and that the reduced confidence in OC checkers may reflect a disconfirmation bias in this population.

Regulation of phosphate uptake in primary cultured rabbit renal proximal tubule cells by glucocorticoids: evidence for nongenomic as well as genomic mechanisms

We have investigated the nongenomic as well as the genomic effects of glucocorticoids on phosphate (Pi) uptake in primary rabbit renal proximal tubule cells (PTCs) and have defined the involved signaling pathways. In the present study, cortisol-BSA (cortisol-BSA) (>10(-9) M, 30 min) was found to inhibit Pi uptake in a time- and concentration-dependent manner. However, progesterone-BSA (P(4)-BSA), 17ss-estradiol-BSA (E(2)-BSA), testosterone-BSA (T(4)-BSA), aldosterone, P(4), E(2), and T(4) (10(-9) M, 1 h) had no effect on Pi uptake. In addition, cortisol-BSA (10(-9) M) did not affect either Na(+) uptake or alpha-methylglucopyranoside (alpha-MG) uptake. The cortisol-BSA-induced inhibition of Pi uptake was associated with a decrease in the V(max) for Pi uptake, rather than the K(m). The inhibitory effect of cortisol-BSA was not blocked either by actinomycin D (an inhibitor of transcription), cycloheximide (an inhibitor of translation), or classical glucocorticoid receptor antagonists (RU 486 or P(4)). The cortisol-BSA-induced inhibition of Pi uptake was blocked by two phospholipase C (PLC) inhibitors (neomycin or U73122), and two protein kinase C (PKC) inhibitors (staurosporine or bisindolylmaleimide I) but not by two adenylate cyclase/protein kinase A inhibitors [SQ 22536 (an adenylate cyclase inhibitor) or myristoylated protein kinase A inhibitor amide 14-22]. Furthermore, cortisol-BSA promoted the translocation of PKC from the cytosolic fraction to the membrane fraction, while having no effect on the activity of adenylate cyclase. Our observations may thus be interpreted as indicating that cortisol does indeed inhibit renal Pi uptake via a nongenomic mechanism, which involves the PLC/PKC pathway.

Realism of confidence in obsessive-compulsive checkers

The study examined whether obsessive-compulsive (OC) checkers have reduced confidence in their knowledge. OC checkers were compared with panic disorder (PD) patients and nonpatient controls using a calibration-of-knowledge procedure. Participants completed a general knowledge questionnaire, rated their confidence in each answer, and estimated the total number of correct answers. These responses were converted to 2 measures of confidence relative to performance--over/underconfidence and over/underestimation. OC checkers had lower scores than nonpatients did on both measures, whereas the PD patients did not differ from either group. For the OC checkers, relative confidence was inversely related to the severity of obsessions. The authors speculate that confidence may depend on a confirmation bias in testing hypotheses and that the reduced confidence in OC checkers may reflect a disconfirmation bias in this population.

Mechanism of regulation of Na+ transport by angiotensin II in primary renal cells

BACKGROUND

Angiotensin II (Ang II) has a dose-dependent, biphasic effect on the activity of the Na+/H+ antiport system in the renal proximal tubule (RPT). The aim of the present study was to further delineate the signaling pathways involved in Ang II action.

METHODS

To examine Ang II signaling, 22Na+ uptake studies were conducted with a primary rabbit RPT cell culture system. The activation of phospholipase A2 (PLA2) was assessed by measuring the release of [3H]-arachidonic acid (AA), and changes in intracellular calcium levels were determined by means of confocal microscopy.

RESULTS

Low dosages of Ang II (<10-10 mol/L) stimulated Na+ uptake, whereas high dosages of Ang II (>10-10 mol/L) inhibited Na+ uptake. Ang II (>10-10 mol/L) also caused an increase in AA release associated with an increase in intracellular calcium. Not only did exogenous AA inhibit Na+ uptake, but two PLA2 inhibitors (mepacrine and AACOCF3) blocked the Ang II-mediated inhibition of Na+ uptake. However, the cytochrome P450-dependent epoxygenase inhibitor econazole also blocked the Ang II-induced inhibition of Na+ uptake. Inhibition of Na+ uptake was obtained by the metabolic product of the epoxygenase 5,6-EET. In turn, the inhibitory effect of 5,6-EET was blocked by indomethacin.

CONCLUSIONS

The results indicate the involvement of a calcium-dependent PLA2 in mediating the inhibitory effect of Ang II on Na+ uptake. The AA, which is released following PLA2 activation, acts indirectly, through its own metabolism, via a cytochrome P450 epoxygenase pathway and ultimately cyclooxygenase itself.

Pantomography vs mandibular series for the detection of mandibular fractures

OBJECTIVE

The two primary radiographic techniques used for the evaluation of mandible injury are a pantomographic series (PS) and the standard four-view mandibular series (MS). Despite a tenuous foundation, there is apparent bias in favor of PS compared with MS. Many emergency departments do not have ready access to the specialized equipment necessary to perform a pantomographic study. The hypothesis of this study was that a high-quality standard MS is as sensitive and specific as a PS in the detection of mandibular fractures.

METHODS

This was a prospective, blinded study of 54 patients presenting with acute mandibular injury comparing MS and PS. The study design used two board-certified emergency physicians and a single staff radiologist who read a series of MS and PS films in a randomized fashion without access to clinical information or identifying patient data. The absolute number of fractures present was determined by a neuroradiologist with access to both MS and PS simultaneously as well as pertinent clinical information.

RESULTS

Thirty patients had 47 mandibular fractures. The sensitivity for fracture detection for each physician was 0.85, 0.77, and 0.89 with MS and 0.79, 0.74, and 0.83 with PS (p > or = 0.51, p > or = 1.00, and p > or = 0.51, respectively, McNemar's binomial test). The specificity for fracture detection for each physician was 0.88, 0.92, and 0.96 for MS and 0.96, 1.00, and 0.92 for PS (p > 0.625, p > 0.50, and p = 1.00, respectively, McNemar's binomial test).

CONCLUSIONS

A standard mandibular series is as sensitive and specific as pantomography in the detection of mandibular fractures.

Response to missile attacks on civilian targets in patients with panic disorder

BACKGROUND

The complex interaction that exists between biological and cognitive factors determines the reaction of panic-disorder patients to stressors. The current study was conducted to systematically assess the behavioral effects of a real, life-threatening event on panic-disorder patients.

METHOD

Sixty-five panic-disorder patients completed structured telephone interviews during the first 4 weeks of the Persian Gulf War. Evaluation included frequency of panic attacks, anxiety levels, and function levels both during and between air raid alarms.

RESULTS

The findings indicate that panic-disorder patients, despite high levels of anxiety, did not demonstrate an increased frequency of panic attacks during the Persian Gulf War. In addition, the majority of patients reported good-to-high levels of functioning during the crisis in both everyday and alarm-related functioning. Grouping of subjects according to proximity to risk or current antipanic treatment did not produce significant differences in the frequency of panic attacks or levels of anxiety.

CONCLUSION

The findings suggest that vulnerability of patients with panic disorder to a "panic-stricken" response does not increase during real-life stressors. The lack of increased frequency of panic attacks observed under these circumstances provides additional support for the opinion that panic and fear are two distinct entities.

Toxicity of ifosfamide and its metabolite chloroacetaldehyde in cultured renal tubule cells

Renal injury is a common side effect of the chemotherapeutic agent ifosfamide. Current evidence suggests that the ifosfamide metabolite chloroacetaldehyde may contribute to this nephrotoxicity. The present study examined the effects of ifosfamide and chloroacetaldehyde on rabbit proximal renal tubule cells in primary culture. The ability of the uroprotectant medication sodium 2-mercaptoethanesulfonate (mesna) to prevent chloroacetaldehyde-induced renal cell injury was also assessed. Chloroacetaldehyde (12.5-150 microM) produced dose-dependent declines in neutral red dye uptake, ATP levels, glutathione content, and cell growth. Coadministration of mesna prevented chloroacetaldehyde toxicity while pretreatment of cells with the glutathione-depleting agent buthionine sulfoximine enhanced the toxicity of chloroacetaldehyde. Ifosfamide (1000-10,000 microM) toxicity was detected only at concentrations of 4000 microM or greater. Analysis of media collected from ifosfamide-treated cell cultures revealed the presence of several ifosfamide metabolites, demonstrating that renal proximal tubule cells are capable of biotransforming this chemotherapeutic agent. This primary renal cell culture system should prove useful in studying the cause and prevention of ifosfamide nephrotoxicity.

A double-blind crossover comparison of clomipramine and desipramine in the treatment of panic disorder

OBJECTIVE

To compare the efficacy of clomipramine hydrochloride (CMI), a serotonin reuptake inhibitor with the noradrenergic tricyclic antidepressant agent, and desipramine hydrochloride (DMI) for patients with panic disorder (PD).

METHOD

Following a 2-week, single-blind placebo washout phase, 17 PD outpatients completed a 16-week, double-blind, crossover comparison of CMI and DMI. Key outcome measures included panic attacks frequency, the NIMH Global Scales for Anxiety, Depression and Impairment, Hamilton Anxiety Scale (Psychic and Somatic Subscales), Zung Anxiety Inventory (Raw and Index Subscales) and the Spielberger State Anxiety Scale.

RESULTS

Both CMI and DMI led to significant improvement from baseline placebo state in panic attacks frequency and behavioral ratings (p<0.001). CMI led to a greater reduction in the frequency of panic attacks (p=0.028) and was superior to DMI on ratings of anxiety: NIMH Global Anxiety, Zung Anxiety Scale (Raw and Index) and the Spielberger Anxiety Scale. No difference was found between the drugs on the NIMH Global Impairment Scale and the Hamilton Somatic and Psychic Scales.

CONCLUSION

Both drugs appeared to have significant therapeutic effects in patients with PD, but CMI appeared to be more effective. The effectiveness of the serotonergic drug suggests that the role of the serotonergic system in the pathogenesis of PD should be further explored.

Response of primary rabbit kidney proximal tubule cells to estrogens

The effects of estrogens on the growth and function of primary rabbit kidney proximal tubule (RPT) cells have been examined in hormonally defined phenol red-free medium. 17beta-estradiol was observed to stimulate growth at dosages as low as 10(-10) M. The growth stimulatory effects of 17beta-estradiol were mitigated in the presence of hydrocortisone, suggesting that these two steroid hormones acted at least in part by common mechanisms. The effects of other steroids known to interact with the estrogen receptor were examined. Alpha estradiol was found to be growth stimulatory over a concentration range of 10(-9) to 10(-8) M, albeit to a lower extent than beta estradiol. In addition, the anti-estrogen tamoxifen was also growth stimulatory (unlike the case with the human mammary tumor cell line MCF-7). The effects of several metabolic precursors of 17beta-estradiol were examined, including testosterone, which was growth stimulatory, and progesterone, which was growth inhibitory. The growth stimulatory effects of 17beta-estradiol, alpha estradiol, and tamoxifen could possibly be explained by their interaction with an estrogen receptor. Indeed, metabolic labelling and immunoprecipitation studies indicated the presence of such an estrogen receptor in the primary cultures. The rate of biosynthesis of the estrogen receptor was found to be affected by the presence of exogenously added 17beta-estradiol. 17beta-estradiol was also observed to increase the activity of two brush border enzymes, alkaline phosphatase and gamma glutamyl transpeptidase, during the growth phase of the primary cultures.

Colloidal silica-coated tissue culture dishes for primary cell cultures: growth of rabbit renal proximal tubule cells

The use of colloidal silica as a substratum for primary cultures of differentiated cells has significant advantages over classic tissue culture polystyrene. In this report, the growth and the level of expression of differentiated function of primary rabbit renal proximal tubule (RPT) cell cultures on colloidal silica is examined, using hormonally defined serum-free medium. Primary RPT cells grew to confluence more rapidly on colloidal silica than on tissue culture polystyrene (TC+). Moreover, following three passages, the RPT cells increased in number threefold more than parallel cultures on TC+. The morphology of primary RPT cells on colloidal silica were found by means of transmission electron microscopy to possess a polarized morphology with a brush border, and differentiated markers were retained even after passaging, including the Na+/glucose cotransport system and Glut 7.

Primary kidney cells

Primary rabbit kidney epithelial cell cultures can be obtained that express renal proximal tubule functions. Toward these ends, renal proximal tubules are purified from the rabbit kidney by the method of Brendel and Meezan. To summarize, each kidney is perfused with iron oxide, which becomes associated with glomeruli. The renal cortex is sliced and homogenized to liberate nephron segments. Renal proximal tubules and glomeruli are purified by sieving. The glomeruli, covered with iron oxide, are removed using a magnet. After a brief collagenase treatment (to disrupt basement membrane), the tubules are plated in hormonally defined serum-free medium supplemented with 5 μg/mL bovine insulin, 5 μg/mL human transferrin, and 5 × 10⁻⁸M hydrocortisone. After 5–6 d of incubation, confluent monolayers are obtained that possess multicellular domes, indicative of their capacity for transepithelial solute transport.

Advanced prostate cancer. Endocrine therapies and palliative measures

Management of patients with metastatic prostate cancer differs from that of patients with other metastatic solid tumors. Because the treating physician is usually the patient's urologist, the primary care physician's main role may be to relieve pain and treat the patient for common side effects of hormone therapies. By being familiar with the forms of systemic treatment-including orchiectomy and the use of estrogens, luteinizing hormone-releasing hormone agonists, and antiandrogens-the primary care physician can also assist patients in making treatment decisions that are individualized to the specifics of disease state, comorbid conditions, age, and value systems.

Increased prevalence of the Taq I A1 allele of the dopamine receptor gene (DRD2) in obesity with comorbid substance use disorder: a preliminary report

In order to investigate the prevalence of the Taq I A1 allele of the dopamine receptor gene (DRD2) in obesity with and without comorbid substance use disorder, a total of 40 patients, from an outpatient neuropsychiatric clinic in Princeton, New Jersey, were genotyped for presence or absence of the Taq I DRD2 A1 allele. The primary inclusion criterion for 40 obese subjects was a body mass index (BMI) equal to or over 25 (uncharacterized); 11 obese subjects had severe substance use disorder; 20 controls had a BMI below 25; and, 33 substance use disorder (less severe) patients had a BMI below 25. The data were statistically compared with three different sets of controls divided into three separate groups (Group I, n = 20; Group II, n = 286; Group III, n = 714). They differed according to screening criteria (drug, alcohol, nicotine abuse/dependence, BMI below 25 and other related behaviours including parental history of alcoholism or drug abuse and DSM IV, Axis I and Axis II diagnoses). Groups II and III were population controls derived from the literature. The prevalence of the Taq I A1D2 dopamine receptor (DRD2) alleles was determined in 40 Caucasian obese females and males. In this sample with a mean BMI of 32.35 +/- 1.02, the A1 allele of the DRD2 gene was present in 52.5% of these obese subjects. Furthermore, we found that in the 23 obese subjects possessing comorbid substance use disorder, the prevalence of the DRD2 A1 allele significantly increased compared to the 17 obese subjects without comorbid substance use disorder. The DRD2 A1 allele was present in 73.9% of the obese subjects with comorbid substance use disorder compared to 23.5% in obese subjects without comorbid substance use disorder. Moreover, when we assessed severity of substance usage (alcoholism, cocaine dependence, etc.) increasing severity of drug use increased the prevalence of the Taq I DRD2 A1 allele; where 66.67% (8/12) of less severe probands possessed the A1 allele compared to 82% (9/11) of the most severe cases. Linear trend analyses showed that increasing use of drugs was positively and significantly associated with A1 allelic classification (p < 0.00001). These preliminary data suggest that the presence of the DRD2 A1 allele confirms increased risk not only for obesity, but also for other related addictive behaviours (previously referred to as the Reward Deficiency Syndrome) and that a BMI over 25 by itself (without characterization of macroselection or comorbid substance use disorders) is not a sufficient criterion for association with the DRD2 A1 allele.

Effect of prolonged administration of dietary capsaicin on broiler growth and Salmonella enteritidis susceptibility

The effect of continuous (42 days) dietary administration of 5 or 20 ppm capsaicin to broiler chickens on Salmonella enteritidis susceptibility, body weight, and feed efficiency was investigated. Chickens were weighed at 1, 21, and 42 days of age. No significant differences in body weight or feed efficiency were observed. Chickens were challenged with 1 x 10(8) colony-forming units of S. enteritidis at 21, 28, or 42 days of age. The S. enteritidispositive culture rate for cecal tonsils was significantly lower (P < 0.05) in the treatment groups receiving 5 ppm or 20 ppm dietary capsaicin than in the untreated control group at all challenge times. Dietary capsaicin (5 and 20 ppm) resulted in protection against S. enteritidis organ invasion at 28 days in one experiment and at both 21 and 42 days in the other. These results indicate that continual dietary capsaicin administration increases resistance to S. enteritidis colonization and organ invasion throughout the normal growth period without detrimental effects on growth in broiler chickens.

Uptake and phosphorylation of thiamine in rabbit primary proximal tubule cells and Madin Darby canine kidney cells. II. Effect of ethanol

Uptake of [14C]thiamine was studied in renal primary proximal tubule cells and in Madin Darby Canine Kidney cells in culture. Findings were compared with data for the accumulation of [14C]thiamine and its phosphorylation in renal cortical slices. There was a saturable component for thiamine uptake in all cell types. When normalized for milligrams of protein, renal cortical slices accumulated 82% less 14C than renal primary proximal tubule cells and 51% less than distal tubule cells. Maximal [14C]thiamine levels accumulated by the saturable component was 1.33 nmol/g in slices and 7.02 nmol/g in proximal tubule cells. Ethanol, at 25 mM, inhibited thiamine uptake and phosphorylation in the cell cultures similar to its effect in the kidney tissue.

Emergence of depressive symptoms during treatment for panic disorder with specific 5-hydroxytryptophan reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRI) have been established as effective drugs in the treatment of depressive and anxiety disorders. However, there are also reports that they can induce depressive symptoms and suicidal thoughts in patients. Eighty of 230 patients who met the DSM-III-R criteria for panic disorder received, during the course of treatment, fluvoxamine (a selective serotonin reuptake inhibitor) at a dose level between 50-200 mg/day. The patients were clinically evaluated for a history of affective disorder and for the presence of affective symptoms before the treatment and for emergence of depressive symptoms during the treatment. Seven of the 80 patients (9%) developed symptoms of depression despite a good antianxiety response. Five of the 7 patients received fluvoxamine as second choice after tricyclic antidepressants (TCA). These patients had no history of affective disorder, and no symptoms of depression were present before the treatment with fluvoxamine. The depressive symptoms abated after the fluvoxamine was discontinued and TCA or clonazepam was prescribed. The depressive symptoms reappeared when fluoxetine was administered. None of these 7 patients developed depressive symptoms while treated with TCA or clonazepam. Among the 150 patients treated with TCA and benzodiazepines, not a single case of depression was seen in patients without a previous history of depression. These results suggest a vulnerability among some of panic disorder patients to noradrenergic-serotonergic imbalance caused by SSRI, which has to be taken into clinical consideration.

Phospholipids regulate growth and function of MDCK cells in hormonally defined serum free medium

The effects of the simple phospholipids phosphatidic acid (PA) and lysophosphatidic acid (LPA) on the growth and function of Madin Darby Canine Kidney (MDCK) cells has been studied. We observed that PA and LPA not only stimulated the growth of MDCK cells (at 20 microM), but also stimulated the growth of normal rabbit kidney cells in serum free medium (albeit at a lower dosage of 5 microM). Evidence was obtained that PA interacts synergistically with insulin so as to elicit a growth stimulatory effect. Recently, extracellular PA and LPA were proposed to stimulate mitogenesis in several types of animal cells by binding to particular sites on the plasma membrane which are coupled to signaling mechanisms such as adenylate cyclase via a pertussis toxin sensitive, inhibitory guanosine triphosphate binding protein (Gi protein) (15). However, even when the pertussis toxin dosage was increased to 50 ng/ml, LPA still had a dramatic growth stimulatory effect on MDCK cells. In the absence of LPA pertussis toxin was slightly growth stimulatory to MDCK cells. Phospholipids such as PA and LPA have been observed to prevent prostaglandin-induced increases in adenylate cyclase activity in other cell types via their effects on such a pertussis toxin sensitive Gi protein. If PA and LPA act on MDCK cells in this manner, then these phospholipids may possibly prevent the effect of PGE1 on the growth of normal MDCK cells. However PGE1 was still growth stimulatory to normal MDCK cells. The effects of PA on PGE1 independent variants of MDCK cells, which have elevated intracellular cyclic AMP levels (22), were also examined. In the presence of PA, PGE1 remained growth inhibitory, rather than growth stimulatory to the PGE1 independent cells. However, the PA dosage required to elicit an optimal growth response (5 microM) was dramatically reduced, as compared with normal MDCK cells (20 microM). This altered dosage requirement could be explained by the elevated intracellular cyclic AMP levels in the PGE1 independent variants. Like PGE1 and 8-bromocyclic AMP, PA and LPA also significantly increased the initial rate of Rb+ uptake by confluent monolayers of MDCK cells. The increase in the initial rate of Rb+ uptake could be explained by an increase in the ouabain-sensitive component of Rb+ uptake. An increase in the initial rate of ouabain-insensitive Rb+ uptake was also observed in LPA treated MDCK cell cultures.

Growth and function of primary rabbit kidney proximal tubule cells in glucose-free serum-free medium

The properties of primary rabbit kidney proximal tubule cells in glucose-free serum-free medium have been examined. Primary rabbit kidney proximal tubule cells were observed to grow at the same rate, 1.0 doublings/day, both in glucose-free and in glucose-supplemented medium. Growth in glucose-free medium was dependent upon the presence of an additional nutritional supplement, such as glutamine, pyruvate, palmitate, lactate, or beta hydroxybutyrate. Lactate, pyruvate, and glutamate are utilized for renal gluconeogenesis in vivo. The growth of the primary rabbit kidney proximal tubule cells in glucose-free medium was also dependent upon the presence of the three growth supplements insulin, transferrin, and hydrocortisone. Insulin was growth stimulatory to the primary proximal tubule cells in glucose-free medium, although insulin causes a reduction in the phosphoenolpyruvate carboxykinase (PEPCK) activity in these cells. PEPCK is a key regulatory enzyme in the gluconeogenic pathway. In order to evaluate whether or not the primary cells have gluconeogenic capacity, their glucose content was determined. The cells contained 5 pmoles D-glucose/mg protein. However, no significant glucose was detected in the medium. Presumably, the primary cells were either utilizing or storing the glucose made by the gluconeogenic pathway. Consistent with this latter possibility, cellular glycogen levels were observed to increase with time in culture. The effect of glucose on the expression of the alpha I(IV) collagen and laminin B1 chain genes was examined. Northern analysis indicated that the level of alpha I(IV) collagen mRNA was significantly elevated in glucose containing, as compared with glucose deficient, medium. In contrast, laminin B1 chain mRNA levels were not significantly affected by the glucose content of the medium.

Retinoic acid inhibits basement membrane protein biosynthesis while stimulating dome formation by Madin Darby canine kidney cells in hormonally defined serum-free medium

The effect of retinoic acid on basement membrane protein biosynthesis and dome formation by Madin Darby canine kidney cells was examined. Retinoic acid inhibited the biosynthesis of laminin, collagen IV, and heparan sulfate proteoglycan by confluent MDCK monolayers in a hormonally defined serum-free medium. Retinoic acid inhibited laminin biosynthesis by as much as 70% after an 8 day incubation period. The inhibitory effect of retinoic acid on laminin biosynthesis preceded temporally the stimulatory effect of retinoic acid on dome formation. This observation is consistent with the existence of a causal relationship between these two phenomena. Not only did retinoic acid inhibit the biosynthesis of laminin, but in addition the biosynthesis of the cellular 67 kd laminin binding protein was inhibited.

Insulin and other regulatory factors modulate the growth and the phosphoenolpyruvate carboxykinase (PEPCK) activity of primary rabbit kidney proximal tubule cells in serum free medium

Insulin was observed to modulate the growth and the phosphoenolpyruvate carboxykinase (PEPCK) activity of primary cultures of rabbit renal proximal tubule cells in serum free medium. Insulin was stimulatory to primary proximal tubule cell growth at a concentration of 10(-8) M. In contrast, insulin was inhibitory to a proximal tubule function, PEPCK activity, following a 5-minute incubation period. An insulin dosage as low as 10(-10) M was inhibitory to PEPCK activity, suggesting the involvement of insulin receptors. Although insulin was required at a significantly higher dosage to stimulate the growth of the primary renal proximal tubule cells than to inhibit PEPCK activity, the elevated dosage required in order to observe a growth effect may be explained by the degradation of insulin by the primary renal proximal tubule cells. However the possible involvement of receptors for Insulin-like Growth Factor I (IGF-I) and Insulin-like Growth Factor II (IGF-II) in mediating the effects of insulin cannot be excluded. Other effector molecules were also examined with respect to their effects on PEPCK activity. The possible involvement of cyclic AMP in the control of the PEPCK activity of the primary renal cells was indicated by the stimulatory effects of 8 bromocyclic AMP, isobutyl methylxanthine (a cyclic AMP phosphodiesterase inhibitor), and forskolin (an activator of adenylate cyclase). Phorbol 12-myristate 13-acetate (TPA), which activates protein kinase C, was inhibitory. The actions of these effector molecules and insulin on the PEPCK activity of the primary renal cultures are remarkably similar to their effects on hepatic PEPCK. Several growth factors, fibroblast growth factor (FGF), and transforming growth factor beta (TGF beta) were also examined. FGF was observed to be stimulatory, whereas TGF beta was inhibitory to the PEPCK activity of the primary renal proximal tubule cells.

Epidermal growth factor or transforming growth factor alpha is required for kidney tubulogenesis in matrigel cultures in serum-free medium

The ability of matrigel, a reconstituted basement membrane gel, to induce the differentiation of baby mouse kidney cells has been examined in a hormonally defined serum-free medium. Primary cultures of baby mouse kidney cells were observed to form tubules over a time interval of 1-2 weeks in matrigel. Electron microscopic studies showed that tubules with lumens were present, and the tubule morphology was similar to that of the collecting duct. When using matrigel from which the growth factors had been removed, tubule formation no longer occurred, unless the medium was further supplemented with epidermal growth factor (10 ng/ml). Transforming growth factor alpha stimulated tubule formation as effectively as epidermal growth factor, whereas transforming growth factor beta had an inhibitory effect on tubule formation. These data suggest that both an extracellular matrix and specific growth factors may regulate kidney differentiation during development.

Altered basement membrane protein biosynthesis by primary cultures of cpk/cpk mouse kidney

Previously, kidneys from three-week-old cpk/cpk C57/B16 mice were found to contain elevated mRNA levels for the basement membrane components collagen IV and laminin [1]. Here primary cultures of kidney epithelial cells derived from cpk/cpk C57/B16 mice were established and the production of these proteins in culture was studied. Primary cultures of cpk/cpk mouse kidney epithelial cells were observed to have a more polygonal, flattened morphology than cells from unaffected littermate kidneys. The rate of collagen IV and laminin biosynthesis was determined by means of [35S] labelling studies followed by immunoprecipitation. Collagen IV and laminin biosynthesis are elevated by approximately twofold or more in primary cultures derived from 20-day-old cpk/cpk mice, as compared with parallel primary cultures derived from their unaffected littermates. Similarly, laminin B1 chain mRNA is elevated in primary cultures derived from 20-day-old cpk/cpk mice. In primary cultures derived from younger (day 11) mice, similar differences in the rates of both collagen and laminin biosynthesis were not observed between the two culture types. These observations are consistent with the previously reported age-dependent differences observed in laminin and in collagen IV gene expression in both cpk/cpk and wild-type mouse kidneys, and suggest that the regulation of overproduction of these proteins is due to an alteration in the kidney cells and not due to systemic factors.

Retinoic acid modulates dome formation by MDCK cells in defined medium

Retinoic acid dramatically increases the size of domes in confluent MDCK monolayers in a hormonally defined medium (medium K-1). After 4-5 days of retinoic acid treatment, enlarged domes began to appear in confluent MDCK monolayers. After 7 days with 3 x 10(-7) M retinoic acid, the majority of the domes in the monolayers were between 27 and 80 x 10(-3) microns 2 in area, whereas in control medium the majority of the domes were between 0 and 9 x 10(-3) microns 2 in area. The dependence of the retinoic acid effect on prostaglandin E1 (PGE1) was examined. In normal MDCK cells, the effects of retinoic acid on dome size were observed only in medium K-1 supplemented with PGE1. This observation indicated that retinoic acid did not elicit its effects simply by stimulating PGE production. In contrast, in monolayers of PGE1-independent MDCK cells, retinoic acid treatment resulted in an increase in dome frequency even in medium K-1 lacking PGE1. This observation can be explained by the elevated cyclic adenosine monophosphate (cAMP) levels in these PGE1-independent MDCK cells. Dibutyryl cAMP-resistant MDCK cells, which normally do not form domes in medium K-1, were also studied. Remarkably, the dibutyryl cAMP-resistant MDCK cells were observed to form domes at a significant frequency when medium K-1 was supplemented with retinoic acid. However in medium K-1 lacking PGE1, an effect of retinoic acid on dome formation by dibutyryl cAMP-resistant MDCK monolayers was not observed. The inability of dibutyryl cAMP-resistant MDCK cells to form domes in medium K-1 has previously been attributed to their decreased cAMP-dependent protein kinase activity. The stimulatory effects of retinoic acid on dome formation may possibly be due to an increase in the activity of a particular cAMP-dependent protein kinase or activation of a separate pathway.

Preparation of basolateral membranes that transport p-aminohippurate from primary cultures of rabbit kidney proximal tubule cells

The organic anion p-aminohippurate (PAH) is specifically secreted by the renal proximal tubule. The possibility was examined that the probenecid sensitive PAH transport system (which is involved in this secretory process in renal proximal tubule cells in vivo) is retained in primary cultures of rabbit kidney proximal tubule cells. Significant 3H-PAH uptake into primary cultures of proximal tubule cells was observed. After 10 min, 150 pmole PAH/mg protein had accumulated intracellularly. Given an intracellular fluid volume of 10 microliter/mg protein, the intracellular PAH concentration was estimated to be 15 microM. The initial rate of PAH uptake (when 50 microM PAH was in the uptake buffer) was inhibited 50% by 2 mM probenecid. Intact monolayers also exhibited Na+-dependent alpha methyl-D-glucoside uptake (an apical marker). Basolateral membranes were purified from primary rabbit kidney proximal tubule cell cultures. Probenecid sensitive PAH uptake into the membrane vesicles derived from the primary cultures was observed. The rate of PAH uptake was equivalent to that obtained with vesicles obtained from the rabbit renal cortex. No significant Na+-dependent D-glucose uptake into the vesicles was observed, indicating that primarily basolateral membrane vesicles had indeed been obtained.

Dibutyryl cyclic AMP resistant MDCK cells in serum free medium have reduced cyclic AMP dependent protein kinase activity and a diminished effect of PGE1 on differentiated function

Prostaglandin E1 (PGE1) has a stimulatory effect both on the growth and the expression of differentiated function of Madin Darby Canine Kidney (MDCK) cells in a hormonally defined medium (Medium K-1). While the stimulatory effect of PGE1 on MDCK cell growth is observed in subconfluent cultures, the effect of PGE1 on differentiated function (i.e., dome formation) is observed at confluency. PGE1 may possibly affect growth and such differentiated functions by separate mechanisms. In order to examine this possibility, dibutyryl cyclic AMP resistant variants of MDCK were selected. All of the variants were partially resistant to the growth inhibitory effects of dibutyryl cyclic AMP and theophylline. The cyclic AMP dependent protein kinase activity of four of the five variant clones studied was significantly reduced as compared with normal MDCK cells. The dependence of the kinase activity of several of the dibutyryl cyclic AMP resistant variants (DBr2 and DBr3) on the cyclic AMP concentration in the reaction mixture was compared with that of normal MDCK cells. At all of the cyclic AMP concentrations tested DBr2 and DBr3 cells had reduced protein kinase activity as compared with normal MDCK cells. This reduced activity could be attributed to a decrease in the Vmax for kinase in the two variants, rather than to a change in the Km of kinase for cyclic AMP. The cyclic AMP phosphodiesterase activity of dibutyryl cyclic AMP resistant variants was also studied. Unlike PGE1 independent clone 1, DBr2 and DBr3 cells did not differ significantly from normal MDCK cells with regard to their ability to degrade cyclic AMP. The growth and functional responsiveness of DBr2 and DBr3 cells to PGE1 was also examined. DBr2 and DBr3 cells were shown to retain a normal growth response to PGE1. However the capacity of DBr2 and DBr3 cells to form domes in response to PGE1 was dramatically reduced as compared with normal MDCK cells. Nevertheless DBr3 cells were shown to still retain the capacity to form domes in response to other inducers. The effect of PGE1 on one of the functional parameters involved in dome formation (the activity of the Na+/K+ATPase) was examined. The rate of ouabain-sensitive Rb+ uptake was observed to be elevated in confluent monolayers of normal MDCK cells maintained in Medium K-1, as compared with monolayers maintained in Medium K-1 minus PGE1.(ABSTRACT TRUNCATED AT 400 WORDS)

Phosphate uptake by primary renal proximal tubule cell cultures grown in hormonally defined medium

The uptake of labeled inorganic phosphate into primary rabbit kidney proximal tubule cells has been examined. Phosphate was accumulated into the primary proximal tubule cells against a concentration gradient. This accumulation was sensitive to inhibition by metabolic inhibitors. The dependence of phosphate uptake on the extracellular phosphate concentration was examined. Similarities were observed between primary proximal tubule cells and the LLC-PK1 cell line in these regards. These phosphate uptake data were then plotted on a Lineweaver-Burke plot. A nonlinear plot was obtained, which suggested that phosphate uptake occurs by means of a Na+ dependent, carrier mediated process, as well as by another Na+ independent mechanism. The pH dependence of phosphate uptake was also examined. Unlike previous observations with LLC-PK1 cells, optimal phosphate uptake occurred at pH 6.5. However, this difference between the two cell culture systems may possibly be explained by differences in uptake conditions. The dependence of phosphate uptake on the extracellular NaCl concentration was examined at three different pH values. The rate of phosphate uptake at pH 7.0 was observed to saturate at a lower NaCl concentration than at either pH 6.0 or pH 6.5. Furthermore, the optimal rate of phosphate uptake at pH 7.0 was observed to be higher than at the other two pH values studied when the NaCl concentration was below 120 mM. However, when the NaCl concentration was raised to 150 mM, optimal phosphate was observed to occur at pH 6.5 rather than at pH 7.0. These observations may be explained if the pH affects not only the rate of phosphate uptake but also the affinity of the phosphate uptake system for sodium. Phosphate uptake was also observed to be sensitive to several agents, Na2 X SO4 and NaSCN, which affect the membrane potential. As observed with phosphate uptake by LLC-PK1 (and renal brush border membrane vesicles), phosphate uptake was highly sensitive to inhibition by the phosphate analogue arsenate. Novel observations were that the phosphate analogue vanadate and its cellular metabolite vanadyl stimulated the initial rate of phosphate uptake.

PGE1-independent MDCK cells have elevated intracellular cyclic AMP but retain the growth stimulatory effects of glucagon and epidermal growth factor in serum-free medium

Prostaglandin E1 (PGE1), a component in the hormone-supplemented, serum-free medium for the Madin Darby canine kidney (MDCK) cell line, has been proposed to increase MDCK cell growth by increasing intracellular cyclic AMP levels. The association between increased intracellular cyclic AMP and the growth stimulatory effect of PGE1 has been examined in normal MDCK cells and in PGE1-independent variants of MDCK. These variant cells have lost the PGE1 requirement for long term growth in defined medium. Normal MDCK cells had almost twofold higher intracellular cyclic AMP levels during growth in Medium K-1 (9.0 pmol/mg protein) than in Medium K-1 minus PGE1. Furthermore, PGE1-independent clone 1 had higher intracellular cyclic AMP levels in Medium K-1 minus PGE1 than normal MDCK cells in Medium K-1. This latter observation suggests that the PGE1 requirement for MDCK cell growth is associated with the low intracellular cyclic AMP levels of this cell line. An involvement of cyclic AMP in the growth response to PGE1 is supported by these observations, as well as by the growth stimulatory effects of other agents that affect cyclic AMP metabolism in MDCK cells. These agents include glucagon, isobutyl methylxanthine (IBMX), and dibutyryl cyclic AMP. The growth of PGE1-independent clone 1 was inhibited rather than stimulated by PGE1. Similarly, PGE1-independent cell growth was inhibited by IBMX and dibutyryl cyclic AMP. However, the growth response to one agent which increases cyclic AMP (glucagon) was retained in PGE1-independent clone 1. This result suggests that the effect of glucagon is not associated with increases in intracellular cyclic AMP. The growth stimulatory effect of epidermal growth factor (EGF) on normal MDCK cells was also studied. Although EGF does not act via a cyclic AMP-mediated mechanism, EGF increased normal MDCK cell growth and substituted for PGE1 in Medium K-1. Thus, EGF and PGE1 could possibly affect similar growth-related functions in MDCK cells, although by different pathways. This possibility was examined further, using PGE1-independent clone 1. EGF, like glucagon, was still growth stimulatory to the PGE1-independent cells. Consequently, the biochemical pathways by which EGF and PGE1 increase MDCK cell growth probably do not converge.

Transport and metabolism of glucose by renal proximal tubular cells in primary culture

A highly purified suspension of rabbit proximal tubules was cultured in a hormone-supplemented serum-free medium. This primary culture yielded a homogeneous population of cells that demonstrated functional and morphological polarity in mono-layers. The characteristics of the Na-dependent glucose transporter in the luminal membrane were studied by measuring the uptake of alpha-methylglucoside (AMG). The kinetics of Na-dependent AMG uptake were consistent with a single saturable system with an apparent Km of 0.8 mM and Jmax of 0.14 nmol X mg-1 X min-1. AMG permeability was 0.10 microliter X mg-1 X min-1. Uptake was inhibited 95% by 0.1 mM phlorizin and by removal of sodium. The stoichiometry of Na/glucose interaction with the carrier was 2:1. These characteristics are typical of the characteristics described for the late proximal tubule. To examine whether the glucose that enters the cell across the luminal membrane is incorporated into the metabolic pool of the cell, we studied the oxidation of [14C]glucose to 14CO2 in the absence and presence of phlorizin. Significant decarboxylation of [1-14C]glucose and [6-14C]glucose was observed, consistent with the existence of aerobic metabolism and a hexose monophosphate shunt. In the presence of 0.1 mM phlorizin, uptake and oxidation of D-glucose were inhibited to an identical degree, suggesting that luminal uptake is a rate-limiting step in the oxidation of glucose by these proximal tubular cells. These studies indicate that proximal tubular cells in primary culture utilize glucose as an energy source and that the glucose derived from transport across the luminal membrane is incorporated into the metabolic pool of the cell.

The solitary thyroid nodule. Selection of patients for surgery

Management of the solitary thyroid nodule, especially the nodule which is hypofunctional on radionuclide scan, is still controversial. The major controversy centers around the selection of patients for surgery. A review of 50 patients who were recently operated on for suspected thyroid cancer at the Naval Regional Medical Center, Portsmouth, Virginia, was undertaken by us in an effort to determine which factors suggest the presence of malignancy preoperatively. Not surprisingly, carcinoma was most frequently found in the solitary, hypofunctional, solid thyroid nodule, although there were exceptions to each of these clinical criteria.

Characterization of primary rabbit kidney cultures that express proximal tubule functions in a hormonally defined medium

Primary cultures of rabbit-kidney epithelial cells derived from purified proximal tubules were maintained without fibroblast overgrowth in a hormone-supplemented serum-free medium (Medium RK-1). A hormone-deletion study indicated that the primary cultures derived from purified rabbit proximal tubules required all of the three supplements in Medium RK-1 (insulin, transferrin, and hydrocortisone) for optimal growth but did not grow in response to EGF and T3. In contrast, the epithelial cells in primary cultures derived from an unpurified preparation of rabbit kidney tubules and glomeruli grew in response to EGF and T3, as well as insulin, transferrin, and hydrocortisone. These observations suggest that kidney epithelial cells derived from different segments of the nephron grow differently in response to hormones and growth factors. Differentiated functions of the primary cultures derived from proximal tubules were examined. Multicellular domes were observed, indicative of transepithelial solute transport by the monolayers. The proximal tubule cultures also accumulated alpha-methylglucoside (alpha-MG) against a concentration gradient. However, little or no alpha-MG accumulation was observed in the absence of Na+. Metabolic inhibitor studies also indicated that alpha-MG uptake by the primaries is an energy-dependent process, and depends upon the activity of the Na+/K+ ATPase. Phlorizin at 0.1 mM significantly inhibited 1 mM alpha-MG uptake whereas 0.1 mM phloretin did not have a significant inhibitory effect. Similar observations have been made concerning the Na+-dependent sugar-transport system located on the lumenal side of the proximal tubule, whereas the Na+-independent sugar transporter on the peritubular side is more sensitive to inhibition by phloretin than phlorizin. The cultures also exhibited PTH-sensitive cyclic AMP synthesis and brush-border enzymes typical of proximal cells. However, the activities of the enzymes leucine aminopeptidase, alkaline phosphatase, and gamma-glutamyl-transpeptidase were lower in the cultures than in purified proximal-tubule preparations from which they are derived.

Treatment of choledocholithiasis with oral chenodeoxycholic acid

The aim of this study was to conduct a controlled trial of oral chenodeoxycholic acid in the management of radiolucent choledocholithiasis. Thirteen patients were randomized in double-blind fashion to receive either 750 mg/day of chenodeoxycholic acid (CDCA) or a placebo. After 4 months, those who had the placebo were administered CDCA; those who had received CDCA and showed a 25% or more decrease in the size of stones (evaluated blindly) received CDCA for an additional 4 months. Five of the 13 patients did not complete the study; four (one initially placebo and three CDCA) because acute biliary symptoms mandated operative intervention and one (initially placebo, then CDCA) because of asymptomatic elevations of the serum transaminase levels. Patients who were withdrawn from the study had significantly larger stones (P less than 0.02) (mean largest diameter, 11.4 mm +/- 1.6 SEM) than those who completed the study (6.5 +/- 0.5). Of the eight patients who completed the study, two of the three who received CDCA initially for 6 to 8 months experienced complete disappearance of stones; all five patients who took the placebo failed to show dissolution, and one of these subsequently had dissolution of stones after 8 months of CDCA. Biliary lipid analyses during treatment showed bile unsaturated with respect to cholesterol in the three patients whose stones dissolved with CDCA therapy. In conclusion, a patient with partial dissolution of stones and unsaturated bile after 4 months of CDCA probably will have complete dissolution of stones after 6 to 8 months of CDCA.

Amiloride-resistant Madin-Darby canine kidney (MDCK) cells exhibit decreased cation transport

Cation transport systems were investigated in mutant Madin-Darby Canine Kidney (MDCK) cells resistant to the diuretic drug amiloride. The mutants were isolated previously as clones resistant to the cytotoxic effects of 3 X 10(-4) M amiloride. Decreased amiloride transport by the Na+ channel was implicated as the basis of the resistance (Taub, '78). Consistent with this hypothesis, Na+ accumulation was lower in amiloride-resistant cells than in normal sensitive MDCK cells. Kinetic studies indicated that Na+ uptake in MDCK cells occurs by a single ATP independent transport system--the Na+ channel. In several amiloride-resistant clones, including clone Amr2, the decreased Na+ uptake was associated with a decrease in both the Km and Vmax for Na+ uptake by the Na+ channel. In Amr2 cells no significant alteration in the inhibitory effect of amiloride on Na+ uptake was observed. As the Na+ channel may actually be a general uptake system for monovalent cations (a number of cations inhibit Na+ uptake), the uptake of these inhibitory cations was examined in Amr2 cells. Both Ca++ and ouabain-insensitive Rb+ uptake occurred at decreased rates in Amr2 cells as compared with normal MDCK cells. However, further uptake studies suggested that Na+, Ca++ and ouabain-insensitive Rb+ uptake all occur by different systems. Thus several transport systems may be defective in Amr2 cells. Amr2 cells were also resistant to the inhibitory effects of amiloride on CO2 evolution from pyruvate. These observations indicate that alterations at a number of molecular sites may be associated with defective Na+ transport via the Na+ channel in amiloride-resistant cells. Thus the amiloride-resistant cells are potentially valuable in examining the interrelationships between Na+ transport and other cellular functions.

Alterations in growth requirements of kidney epithelial cells in defined medium associated with malignant transformation

The possibility has been investigated that 1) the supplements required for the growth of the Madin Darby Canine Kidney (MDCK) cell line in serum-free Medium K-1 are indeed requirements for the growth of normal kidney cells in vitro, and 2) that alterations in these growth requirements are associated with malignant transformation. Consistent with the hypothesis that MDCK cells resemble normal kidney cells in culture, primary cultures of baby mouse kidney epithelial cells grow in Medium K-1 and respond to the 5 components in the medium. The growth properties of Moloney sarcoma virus (MSV)-transformed MDCK cells in defined media have been examined. Unlike MDCK cells, MSV-transformed MDCK cells form tumors in adult nude mice. Although they still respond to the 5 factors in Medium K1, the optimal dosage for insulin is lower for the MSV transformants than for MDCK cells. The MSV transformants also have an additional requirement for growth in Medium K-1-fibronectin. Variants of MDCK cells have been isolated that have lost the PGE1 requirement for growth in defined medium. These variant cells have acquired 1) the ability to form tumors in adult nude mice and 2) an alteration affecting cAMP metabolism, in addition to PGE1 independence.

Growth of functional primary cultures of kidney epithelial cells in defined medium

Primary cultures of baby mouse kidney epithelial cells can grow without fibroblast overgrowth in a hormone-supplemented serum-free medium (Medium K-1) designed for an established kidney epithelial cell line, MDCK. The five supplements in Medium K-1 are insulin, transferrin, PGE1, T3, and hydrocortisone. Medium K-1 also supports the growth of kidney epithelial cell cultures from a number of animals, including man, without fibroblast overgrowth. Outgrowth of kidney epithelial cells from kidney explants was also observed with Medium K-1. Thus, the medium appears to be selective for epithelial cell growth. The physiological properties of primary cultures of baby mouse kidney epithelial cells were studied in detail. Baby mouse kidney epithelial cells grew at equal rates (0.5 doublings/day) in Medium K-1 and serum-supplemented medium. Medium K-1 also supported the formation of baby mouse kidney epithelial colonies at low cell densities. The dependence of baby mouse kidney epithelial colony formation upon the five factors in Medium K-1 was examined. These studies indicated that the formation of baby mouse kidney epithelial colonies in defined medium depended upon all the five supplements in Medium K-1, in a manner similar, although not identical, to MDCK colonies. Primary cultures of baby mouse kidney epithelial cells grown in Medium K-1 retained kidney cell-associated properties, including the ability to form multicellular domes, a phenomenon associated with transepithelial salt transport. Amiloride-sensitive Na+ uptake and the mucosal surface enzyme leucine aminopeptidase were also observed in baby mouse kidney cultures. Similar functions were observed in MDCK monolayers.

Regulation of 22Na+ transport by calcium in an established kidney epithelial cell line

The role of calcium in regulating the Na+ channel in an established kidney epithelial cell line has been examined. Extracellular calcium was inhibitory to Na+ uptake, and a Dixon plot of the initial Na+ uptake rate in the presence of Ca2+ was nonlinear, suggesting a mixed pattern of inhibition. Similar patterns of inhibition were also observed for other divalent cations, including Ba2+, Mg2+, and Mn2+. In contrast elevated concentrations of intracellular calcium resulted in a stimulation of Na+ entry. This intracellular effect was specific to calcium, with Mg2+ and Mn2+ appearing much less effective. Lineweaver-Burk plots of Na+ influx in calcium-loaded and unloaded cells were linear, suggesting that under both conditions a single system transported Na+. Although Na+ entry was stimulated by intracellular Ca2+, the cells did not exhibit other counter transport phenomena reported with cell types in which a Na+/Ca2+ exchange system is operative. Thus, the results indicate that calcium acts as an allosteric regulator of Na+ transport by the Na+ channel.

Uptake of 22Na+ by cultured dog kidney cells (MDCK)

22Na+ uptake measurements were conducted on the dog kidney cell line, MDCK, to determine the mechanism of ouabain-insensitive sodium transport. The radioisotope was found to be taken up into monolayer cultures via an ATP-independent, saturable process (Km = 40 mM). The presence of sodium on the opposite side of the membrane gave rise to a transstimulation of the 22Na+ flux. Studies utilizing potassium and valinomycin suggested that the transport system was insensitive to changes in the membrane potential. Replacement of chloride in the assay buffer with other anions did not decrease the rate of 22Na+ uptake at 14 mMNa+, but bicarbonate and acetate were stimulatory. Potassium and rubidium increased the rate of 22Na+ influx (Ka = 13mM with 14 mM NaCL in the medium). Lithium (Ki = 7.5mM) and amiloride (Ki = 1.7 x 10(-5) M) were competitive and partially (or mixed) competitive inhibitors, respectively. The data are consistent with a mechanism of sodium uptake that includes a carrier(s) capable of catalyzing net sodium uptake and sodium-sodium exchange.