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Biomedical subjects

M Ritter

Publications and source records attributed to M Ritter.

244 records · Page 14Linked to original sources
PubMedDate not supplied

Postprandial gastroesophageal reflux in normal volunteers and symptomatic patients.

A structurally intact and competent lower esophageal sphincter in the experimental model shortens and becomes incompetent during gastric distention. The aim of this study was to evaluate postprandial reflux as an indirect measure of this volume-induced sphincter shortening and incompetency. Reflux (pH <4) in the 2-hour period following a meal was retrospectively analyzed from the 24-hour esophageal pH recordings of 94 healthy volunteers and 609 symptomatic patients. Forty-six percent of patients had pathologic postprandial reflux (>95th percentile of normal). The prevalence was lower in patients with a structurally intact compared to a defective lower esophageal sphincter (32% vs. 58%; P <0.001). Pathologic postprandial reflux was greater in patients with abnormal compared to normal findings on 24-hour pH study (76% vs. 21%; P <0.001). Patients with a normal 24-hour pH study and postprandial reflux had shorter sphincter lengths (2.33 vs. 2.82 cm; P <0.001) and lower pressures (10.78 vs. 14.24 mm Hg; P <0.005). A hiatal hernia increased the prevalence of postprandial reflux (P <0.001) in all patients (67% vs. 38%) and in the subgroup with a structurally intact sphincter (75% vs. 27%, P <0.001). Postprandial reflux is a dynamic indicator of sphincter competency, and increases as the structural sphincter characteristics deteriorate and is augmented by a hiatal hernia.

Adolescent↗
PubMedDate not supplied

Hypotonicity and ethanol modulate BK channel activity and chloride currents in GH4/C1 pituitary tumour cells.

AIM: Description of the effects of hypotonic cell swelling and ethanol on maxi Ca2+-activated K+ channel (BK channel) activity and Cl- channel activity in GH4/C1 pituitary tumour cells. METHODS: Whole cell-, cell attached- and outside-out patch clamp measurements, fluorescence (fluo-3) measurements of intracellular Ca2+ concentration, cell size video monitoring. RESULTS: GH4/C1 pituitary tumour cells respond to both hypotonicity and ethanol with cell swelling which is followed by a regulatory volume decrease (RVD). Tetraethylammonium and 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) induced cell swelling per se and inhibited hypotonicity induced RVD. Ethanol-induced swelling is paralleled by an increase in the intracellular Ca2+ concentration and augmented by DIDS. BK channel activation by hypotonicity and ethanol is demonstrated in patch clamp experiments both in intact cells (cell attached configuration) and a subset of excised membrane patches (outside-out configuration). Cell swelling and addition of ionomycin under isotonic conditions leads to the activation of outwardly rectifying Cl- currents with time dependent activation at positive potentials. CONCLUSIONS: In GH4/C1 cells both hypotonicity and ethanol lead to cell swelling, RVD and to activation of BK channels. The hypotonicity-induced BK channel activation can also be observed in cell free outside-out patches. Hypotonicity, but not ethanol leads to the activation of Cl- channels with features of Ca2+-activated Cl- currents.

3T3 Cells↗
PubMedDate not supplied

The ICln interactome.

The many different functional phenotypes described in mammalian cells can only be explained by an intense interaction of the underlying proteins, substantiated by the fact that the number of independently expressed proteins in living cells seems not to exceed 25 K, a number way too small to explain the >250 K different phenotypes on a one-protein-one-function base. Therefore, the study of the interactome of the different proteins is of utmost importance. Here, we describe the present knowledge of the ICln interactome. ICln is a protein, we cloned and whose function was reported to be as divers as (i) ion permeation, (ii) cytoskeletal organization, and (iii) RNA processing. The role of ICln in these different functional modules can be described best as being a 'connector hub' with 'date hub' function.

Binding Sites↗
PubMedDate not supplied

Microembolus detections at follow-up in 19 patients with acute stroke: correlation with stroke etiology and antithrombotic treatment.

The present study was designed to perform follow-up transcranial Doppler investigations for microembolic signals (MES) in acute stroke patients by means of a strict protocol. The number of MES was correlated with stroke etiology and the strength of antithrombotic treatment. Concurrently, we wanted to demonstrate that MES in acute stroke patients are solid in nature and not gaseous. Nineteen patients with middle cerebral artery ischemic events, 16 with completed stroke and 3 with transient ischemic attack (TIA) were investigated within 24 h following the onset of symptoms. Six 1-hour recordings on days 1, 2, 3, 4, 7 and 14 were performed from the affected middle cerebral artery. The four-gate technique and recently established criteria for the identification of MES were used. Eight of 19 patients showed MES in at least one recording. Variability was high and showed no uniform tendency with respect to time since onset of symptoms or treatment. All 3 patients with internal carotid artery dissection showed MES. In 3 patients with lacunar stroke, no MES were detected. Two patients with MES suffered recurrent TIAs during the observation period, whereas none of the patients without MES suffered a recurrent ischemic event. In the acute phase following stroke, ongoing, emerging and vanishing embolization in some patients may reflect individual active processes of remodelling, healing and disruption or disappearance of the embolic source.

Acute Disease↗
PubMedDate not supplied

Ion channels in Madin-Darby canine kidney cells.

Ion channels in Madin-Darby canine kidney cells serve transepithelial chloride transport and probably cell volume regulation. Three distinct potassium channels and one anion channel have been revealed by patch clamp studies in Madin-Darby canine kidney cells. The potassium channels are activated by an increase in intracellular calcium activity. A number of hormones activate the potassium channels by an increase in intracellular calcium activity. However, under certain conditions the hormones hyperpolarize the cell membrane without increasing intracellular calcium activity sufficiently to activate the calcium-sensitive potassium channels. Thus, the hormones may activate potassium channels via another, as yet undefined, intracellular mechanism. The anion channel is stimulated by cAMP. Another factor modifying channel activity is cell volume: cell swelling leads probably to subsequent activation of potassium and anion channels. The net result is a variable transient hyperpolarization followed by a sustained depolarization of the cell membrane.

Animals↗
PubMedDate not supplied

The biological significance of cell volume.

To survive, cells have to avoid excessive alterations of their volume. To this end, cells have developed a complex machinery of cell volume regulatory mechanisms comprising transport across the cell membrane and metabolism. Upon cell swelling, they loose electrolytes mainly via selective K+ channels and unselective ion channels and/or KCl symport, upon cell shrinkage they accumulate ions by Na+,K+,2Cl- cotransport and parallel operation of Na+/H+ exchange and Cl-/HCO3- exchange. In addition, cell shrinkage stimulates glycogenolysis, proteolysis and formation of organic osmolytes such as amino acids, methylamines and polyols. Cell swelling stimulates formation of glycogen and proteins and cellular release of organic osmolytes. Alterations of cell volume do play a crucial role in the regulation of cell function, as illustrated by four examples: 1. Epithelial transport may lead to cell swelling, which then triggers volume regulatory mechanisms modifying transcellular transport. 2. Insulin swells hepatocytes by activation of Na+,K+,2Cl- cotransport and Na+/H+ exchange, glucagon shrinks those cells by activation of ion channels. The respective volume changes participate in the regulation of cellular protein and glycogen metabolism by these hormones. 3. Growth factors and expression of ras oncogene activate Na+,K+,2Cl- cotransport and Na+/H+ exchange, leading to the respective cell swelling. 4. Hepatocyte swelling triggers a hepatorenal reflex decreasing renal blood flow.

Animals↗
PubMedDate not supplied

Radioimmunoassay of urinary cortisol: comparison of the procedures with and without previous cortisol extraction.

Although only less than 1% of the daily secreted cortisol is excreted unchanged into urine, the determination of urinary cortisol has proved to be a valuable parameter in evaluation of adrenocortical function. We compared the procedures of cortisol determination by radioimmunoassay after extraction and without extraction direct in crude urine. Direct determination needs less tracer and antibody and is less laborious. Intra- and interassay variance is 4.5%, 16.0% in the extraction method and 2.7%, 8.2% in the direct method, respectively. Comparison of both methods is acceptable (r = 0.92), recovery and dilution studies prove the direct method to be correct. Despite a lowered specificity, which gives higher results (factor 1.7) compared to the extraction method, the direct method is entirely sufficient for routine laboratory purposes. It can be achieved without additional equipment by laboratories, which determine total cortisol concentration in plasma.

Humans↗