Model of bicarbonate secretion by resting frog stomach fundus mucosa I. Transepithelial measurements

In the present in vitro experiments on gastric fundus mucosa of Rana esculenta we try to define the mechanism of alkaline secretion that is observed in summer frogs in the resting stomach (blockage of HCl secretion by ranitidine, 10^–5 mol/l). The transepithelial voltage and the rate of alkalinization (ASR) of an unbuffered gastric lumen perfusate was measured as a function of serosal (and mucosal) fluid composition. ASR was high (0.88±S.E. 0.09 Eq·cm^–2·h^–1, n=11) during serosal bath perfusion with HCO₃ ^–-Ringer solution, decreased slightly to 0.50±0.07 Eq·cm^–2·h^–1 (n=6) in HCO₃ ^–-free HEPES-buffered Ringer solution of the same pH, and decreased to approximately 20% when carbonic anhydrase was inhibited by acetazolamide. While replacement of mucosal or serosal Cl^– did not — within 1 h — significantly alter ASR, replacement of serosal Na⁺ in the presence or absence of HCO₃ ^– strongly reduced ASR, and a similar reduction was observed after serosal application of the anion transport inhibitor DIDS (4,4-diisomiocyanatostilbene-2,2-disulphonate, 2·10^–4 mol/l), the metabolic poison rotenone (10^–5 mol/l), the uncoupler dinitrophenol (10^–4 mol/l), and the Na⁺ pump inhibitor ouabain (10^–4 mol/l), while serosal amiloride (10^–4 mol/l) had no effect. These data can be accounted for by a model of alkaline secretion that consists of basolateral HCO₃ ^– uptake from the serosal fluid into the cell via a DIDS-inhibitable Na⁺(HCO₃ ^–)_n-cotransporter and HCO₃ ^– secretion from the cell to the gastric lumen via an anionic conductance pathway. Microelectrode experiments on oxyntopeptic cells reported in the subsequent paper suggest that these cells may also be involved in the resting state alkaline secretion.     

Evidence for rheogenic sodium bicarbonate cotransport in the basolateral membrane of oxyntic cells of frog gastric fundus

Ionic conductance properties of the basolateral cell membrane of oxyntic cells were studied in frog gastric fundus in vitro. After mounting the fundus in a modified Ussing chamber the serosal connective tissue was dissected off and individual oxyntic cells were punctured from the serosal surface with microelectrodes. Under resting conditions the membrane potential averaged –56.9, SD±9.5 mV (n=63), cytoplasm negative. Lowering or raising serosal HCO ₃ ^– concentration from 17.8 to 6 or 36 mmol/l respectively at constant depolarized or hyperpolarized the cell membrane by +16.7 or –18.2 mV respectively. Sudden removal of serosal Na⁺ also depolarized the cell membrane (anomalous Nernst response). Since both the HCO ₃ ^– dependent and the Na⁺ dependent potential changes were strongly depressed by the disulfonic stilbene SITS and since the potential response to HCO ₃ ^– was virtually abolished in Na⁺-free solution we conclude that a rheogenic Na⁺ (HCO ₃ ^– ) _n -cotransport system (n>1) is present in the basolateral cell membrane of oxyntic cells. Its possible role in base transfer during HCl-secretion or HCO ₃ ^– secretion remains to be elucidated.This work was supported by grants Nr. 85.0443.04 and 86.00048.04 from Consiglio Nazionale delle Ricerche, Rome, Italy and by grant Nr. I 37736 from Stiftung Volkswagenwerk, Hannover, FRG     

Adverse drug events resulting from patient errors in older adults

OBJECTIVES: To characterize the types of patient-related errors that lead to adverse drug events (ADEs) and identify patients at high risk of such errors. DESIGN: A subanalysis within a cohort study of Medicare enrollees. SETTING: A large multispecialty group practice. PARTICIPANTS: Thirty thousand Medicare enrollees followed over a 12-month period. MEASUREMENTS: Primary outcomes were ADEs, defined as injuries due to a medication, and potential ADEs, defined as medication errors with the potential to cause an injury. The subset of these events that were related to patient errors was identified. RESULTS: The majority of patient errors leading to adverse events (n=129) occurred in administering the medication (31.8%), modifying the medication regimen (41.9%), or not following clinical advice about medication use (21.7%). Patient-related errors most often involved hypoglycemic medications (28.7%), cardiovascular medications (21.7%), anticoagulants (18.6%), or diuretics (10.1%). Patients with medication errors did not differ from a comparison group in age or sex but were taking more regularly scheduled medications (compared with 0-2 medications, odds ratio (OR) for 3-4 medications=2.0, 95% confidence interval (CI)=0.9-4.2; OR for 5-6 medications=3.1, 95% CI=1.5-7.0; OR for >or=7 medications=3.3, 95% CI=1.5-7.0). The strongest association was with the Charlson Comorbidity Index (compared with a score of 0, OR for a score of 1-2=3.8, 95% CI=2.1-7.0; OR for a score of 3-4=8.6, 95% CI=4.3-17.0; OR for a score of >or=5=15.0, 95% CI=6.5-34.5). CONCLUSION: The medication regimens of older adults present a range of difficulties with the potential for harm. Strategies are needed that specifically address the management of complex drug regimens.     

Differential expression of PTEN gene correlates with phenotypic heterogeneity in three cases of patients showing clinical manifestations of PTEN hamartoma tumour syndrome

Cowden syndrome (CS), Bannayan-Riley-Ruvalcaba syndrome (BRRS) and proteus syndrome are disorders known as PTEN hamartoma tumour syndrome (PHTS), that can show remarkable clinical overlap and are all caused by germline PTEN mutations.We here present two families, one affected by CS and the other affected by BRRS, both carriers of specific pathogenetic missense mutation in exon 5 of PTEN gene, within the catalitic domain. Both PHTS families exhibited extremely variable phenotypes, showing inter- and intra- familial variability. One of the two characterised mutations, the c.320A- > T; p.107Asp- > Val, identified in the CS family, was not previously described in the literature. Furthermore, the BRRS family, carrier of the c.406 T- > C; p.136Cys- > Arg mutation, shows a substantial alteration of PTEN protein expression that well correlates with intra-familial phenotypic variability.Finally, we describe an apparently sporadic case of an 80-year-old man, with a very low level of PTEN mRNA and protein expression, both in healthy and tumour colon mucosa, associated with a very atypical phenotype. He developed a metastatic colorectal carcinoma, macrocephaly and pheochromocytoma.According to literature data, our observations confirm that PTEN mutations of catalytic domain can cause different syndromes. We suggest that PTEN expression could represent one of the mechanisms involved in the remarkable heterogeneity of the clinical PHTS manifestations within affected families. Furthermore, constitutive strong decrease of PTEN expression in colon normal mucosa could be associated with late onset of colorectal cancer.     

Microelectrode determination of oxyntic cell pH in intact frog gastric mucosa. Effect of histamine

Intracellular pH (pH_i) of acid-secreting cells was measured in intact gastric fundus mucosa of Rana esculenta with double-barrelled pH microelectrodes. Tissues were mounted, serosal side up, between two half chambers and individual cells were impaled after microsurgical removal of the serosal muscle layer. Transepithelial potential difference (V _t) and resistance (R _t) as well as serosal cell membrane potential (V _s) and pH_i were continuously recorded at rest (0.1 mmol/l cimetidine) or during stimulation (0.5 mmol/l histamine). During chamber perfusion with HCO3 ₃ ^– /CO₂-buffered Ringer solution of pH_o=7.36, V _t and R _t were –21.7, SD±6.0 mV and 229±83 cm²(n=17) while V _s and pH_i averaged –7.3±6.9 mV and 7.4±0.11 (n=25). The latter value is considerably more alkaline than all recent pH_i measurements obtained with microspectrofluorometric techniques on isolated cells, glands or intact tissue. The difference may in part be explained by use of HCO ₃ ^– -free solutions in most of the previous studies because we observed that such solutions decrease pH_i to 6.89±0.18 (n=4). Again, in contrast to recent literature, application of histamine in HCO ₃ ^– /CO₂-buffered solution led to further transient alkalinization by 0.12±0.05 pH unit (n=8). Since in accidental punctures of the gastric gland lumen we noticed that H⁺ secretion only began approximately 5 min after histamine application, we conclude that the histamine-induced initial alkalinization does not reflect stimulation of the H⁺/K⁺ ATPase pump. Alternatively, it may result from histamine-induced activation or inactivation of other ion transporters, one possibility being activation of basolateral Na⁺/H⁺ and Cl^–/HCO ₃ ^– exchangers.     

The impact of orbitofrontal dysfunction on cocaine addiction

Cocaine addiction is characterized by poor judgment and maladaptive decision-making. Here we review evidence implicating the orbitofrontal cortex in such behavior. This evidence suggests that cocaine-induced changes in orbitofrontal cortex disrupt the representation of states and transition functions that form the basis of flexible and adaptive 'model-based' behavioral control. By impairing this function, cocaine exposure leads to an overemphasis on less flexible, maladaptive 'model-free' control systems. We propose that such an effect accounts for the complex pattern of maladaptive behaviors associated with cocaine addiction.     

Cadmium inhibits acid secretion in stimulated frog gastric mucosa

Cadmium, a toxic environmental pollutant, affects the function of different organs such as lungs, liver and kidney. Less is known about its toxic effects on the gastric mucosa. The aim of this study was to investigate the mechanisms by which cadmium impacts on the physiology of gastric mucosa. To this end, intact amphibian mucosae were mounted in Ussing chambers and the rate of acid secretion, short circuit current (I_sc), transepithelial potential (V_t) and resistance (R_t) were recorded in the continuous presence of cadmium. Addition of cadmium (20 µM to 1 mM) on the serosal but not luminal side of the mucosae resulted in inhibition of acid secretion and increase in NPPB-sensitive, chloride-dependent short circuit current. Remarkably, cadmium exerted its effects only on histamine-stimulated tissues. Experiments with TPEN, a cell-permeant chelator for heavy metals, showed that cadmium acts from the intracellular side of the acid secreting cells. Furthermore, cadmium-induced inhibition of acid secretion and increase in I_sc cannot be explained by an action on: 1) H₂ histamine receptor, 2) Ca²⁺ signalling 3) adenylyl cyclase or 4) carbonic anhydrase. Conversely, cadmium was ineffective in the presence of the H⁺/K⁺-ATPase blocker omeprazole suggesting that the two compounds likely act on the same target. Our findings suggest that cadmium affects the functionality of histamine-stimulated gastric mucosa by inhibiting the H⁺/K⁺-ATPase from the intracellular side. These data shed new light on the toxic effect of this dangerous environmental pollutant and may result in new avenues for therapeutic intervention in acute and chronic intoxication.     

Study of delta sleep-inducing peptide efficacy in improving sleep on short-term administration to chronic insomniacs

The effects of delta sleep-inducing peptide (DSIP), on the sleep cycle of insomniac patients were assessed by means of polysomnographic recordings. DSIP in a dose of 25 nmol/kg or a placebo was administered i.v. during four nights using a double-blind crossover design. The number of nocturnal awakenings, non-rapid-eye-movement (NREM) sleep latency, total waking time and waking time after sleep onset were decreased under DSIP treatment, but no significant differences were found in comparison to baseline or to double-blind placebo nights. Total sleep time and NREM sleep time were increased by the peptide. Their increase was related to increases in stage 2, while stage 1, slow wave sleep (stages 3 and 4) and rapid-eye-movement sleep were not modified. For NREM sleep time and stage 2 sleep differences between DSIP and a placebo were significant, but the same differences existed already for the baseline values. It can be concluded that sleep improvement under DSIP treatment is of little clinical significance.