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M Schramm

Publications and source records attributed to M Schramm.

At least 73 records · Page 4Linked to original sources
PubMed1993

[A simple method of digitizing analog scintigrams for quantification and digital archiving].

This study was undertaken to evaluate a quick, reliable and cheap method of digitizing analog scintigrams. 40 whole-body bone scintigrams were obtained simultaneously in analog and genuine digital format. The analog scans on x-ray film were then digitized secondarily by three different methods: 300 dpi flat-bed scanning, high-resolution camera scanning and camcorder recording. A simple exposure approach using a light box, a cheap camcorder, a PC and image grabber hard- and software proved to be optimal. Visual interpretation showed no differences in clinical findings when comparing the analog images with their secondarily digitized counterparts. To test the possibility of quantification, 126 equivalent ROIs were drawn both in the genuine digital and the secondarily digitized images. Comparing the ROI count to whole-body count percentage of the corresponding ROIs showed the correlation to be linear. The evaluation of phantom studies showed the linear correlation to be true within a wide activity range. Thus, secondary digitalization of analog scintigrams is an easy, cheap and reliable method of archiving images and allows secondary digital quantification.

Analog-Digital Conversion↗
PubMed1992

An endogenous metal appears to regulate NMDA receptor mediated 45Ca influx and toxicity in cultured cerebellar granule cells.

Glutamate induced 45Ca influx and toxicity were enhanced 2-10 fold by EDTA. A chelator concentration of 10 microM, which was equivalent to less than 1% of the Mg2+ and Ca2+ concentration in the medium, was effective. The chelator revealed no activity on its own and caused potentiation only when present simultaneously with the agonist of the NMDA receptor. Cysteine, which is known to bind certain metals tightly through its sulfhydryl group, and another chelator, O-phenanthroline, produced the same effect as EDTA. The findings indicate that when the N-methyl-D-aspartate receptor is activated, an endogenous metal can become bound to a chelator or to a physiological metal binding agent, such as cysteine, leading to enhanced Ca2+ influx into the neuron and toxicity.

Animals↗
PubMed1991

Acute glutamate toxicity in cultured cerebellar granule cells: agonist potency, effects of pH, Zn2+ and the potentiation by serum albumin.

Cell death was due to activation of the receptor responsive to N-methyl-D-aspartate (NMDA). Even during a 30-min incubation, glutamate toxicity was unaffected by 5 microM CNQX and was greater than 90% blocked by 160 nM MK-801, a specific antagonist of the NMDA receptor. The extent of toxicity was dependent on the age of the cultured cells, the concentration of KCl, which determined membrane polarization, the duration of exposure to, and the concentration of, glutamate. Toxicity was critically pH-dependent, increasing from a minimal effect at pH 7.0 to an extremely high level at pH 8.0. Among a number of acidic amino acids tested, glutamate showed the highest potency. Aspartate, cysteine sulfinate and homocysteate reached the same maximal toxicity, but at a 25 times higher concentration. Cysteate and quinolinate were of very low potency. Zn2+, at 0.5 microM, attenuated glutamate toxicity considerably. At concentrations above 5 microM the metal ion showed strong toxicity on its own. Dialysed serum and serum albumin strongly potentiated glutamate and NMDA toxicity in presence and absence of Mg2+. A concentration of 2 mg/ml bovine serum albumin caused maximal potentiation; fatty acid-free bovine serum albumin and human serum albumin were all about equipotent. To be effective, the serum albumin had to act simultaneously with glutamate. Among a number of proteins and other polymers, only casein showed an ability to potentiate glutamate toxicity, similar to serum albumin. It is concluded that minor effects of glutamate toxicity could be considerably aggravated by the potentiating activity of serum albumin, also in pathological situations in vivo.

Amino Acids↗
PubMed1991

Acute glutamate toxicity and its potentiation by serum albumin are determined by the Ca2+ concentration.

Two different processes, mediated by the N-methyl-D-aspartate receptor, appear to cause acute cell death in cultured cerebellar granule cells. A Ca(2+)-independent process takes place at zero and very low concentration of the added cation. Under these conditions, the known destabilization of excitable membranes at low extracellular Ca2+ probably plays a major role. A Ca(2+)-dependent process becomes dominant as its concentration is increased above 1.0 mM. The remarkable potentiation of glutamate toxicity by serum albumin is a calcium-dependent reaction.

Calcium↗
PubMed1990

Culture of mature hippocampus slices for 4 days in a newly developed medium: preservation of transmitter release and leucine incorporation into protein.

A procedure and a medium for sustaining mature hippocampus slices in vitro for 4 days are described. The ionic composition of the medium, in which the slices were incubated for 1 h of recovery following preparation, strongly affected their ability, 4 days later, to take up and to release D-[3H]aspartate and [14C]GABA. A medium deficient in Na+ and Ca2+ proved best for recovery of the fresh slices prior to transfer to culture medium. The newly developed CSF-like culture medium was the best among several media tested in maintaining the potential of the slices for uptake and for induced release of D-[3H]aspartate and [14C]GABA. Glutamine, present in most culture media, appeared to be particularly toxic. Relative to fresh slices, the slices after 4 days in culture maintained 118% and 97% of the uptake of D-[3H]aspartate and of [14C]GABA respectively. K(+)-induced release of D-[3H]aspartate and of [14C]GABA was 104% and 82% of the respective values in fresh slices. Under the optimal culture conditions worked out, the slices also regained a considerable capacity for incorporation of labelled leucine into protein, which was low in fresh slices.

Animals↗
PubMed1990

Synthesis, pharmacological effects, and conformation of 4,4-disubstituted 1,4-dihydropyridines.

4,4-Disubstituted 1,4-dihydropyridines are synthesized by intramolecular addition of sulfinyl carbanions to pyridines. These disubstituted derivatives show a loss of Ca antagonistic potency of up to three powers of 10 both in vitro on aortic rings and in vivo on anaesthetized dogs as compared to examples that are monosubstituted at the 4-position of the DHP ring. As the X-ray structure shows, the 4-aryl substituent is present not in the accustomed axial conformation, but in an equatorial one. This dramatic change in conformation could be the reason for the major loss of activity and would indicate the need for axial conformation of the aryl residue in pharmacologically active 1,4-dihydropyridines. The change in conformation was also confirmed by quantum chemical calculations (AM1).

Animals↗
PubMed1990

Serum and depolarizing agents cause acute neurotoxicity in cultured cerebellar granule cells: role of the glutamate receptor responsive to N-methyl-D-aspartate.

The life span of neonatal rat cerebellar granule cells, grown in basal minimal Eagle's medium containing 10% (vol/vol) fetal calf serum, was extended to 21-30 days by weekly supplementation with glucose. Addition of 1% fetal calf serum to the culture at 14 days killed 85% of the cells within 1 hr. This lethal effect could be prevented by the N-methyl-D-aspartate (NMDA) receptor antagonists dibenzocyclohepteneimine (MK-801) and 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP). These findings suggested that the glutamate in the serum caused the dramatic neuronal death through action on the NMDA receptor. Indeed, a 5-min incubation in a Locke physiological salt solution containing 20 microM glutamate and 5 microM glycine killed 55-90% of the cells. This acute toxicity could be prevented by a lyso-GM1 ganglioside with N-acetylated sphingosine. The relatively low glutamate content of the sera analyzed suggests that factors in addition to glycine potentiate serum neurotoxicity. The above noted antagonists of the NMDA receptor also greatly reduced the lethal effect of depolarization by 90 mM KCl or 10 microM veratridine. Therefore, it is likely that the toxicity of the depolarizing agents is mediated by glutamate released from the cells. It is concluded that survival of cerebellar neurons in primary culture may be strongly affected by unsuspected neurotoxic phenomena elicited by brief action of a rather low glutamate concentration.

Animals↗
PubMed1989

Cysteine sulfinic acid-induced release of D-[3H]aspartate and [14C]GABA in hippocampus slices: the role of sodium channels and cAMP.

Cysteine sulfinic acid, a putative transmitter in the brain induces release of D-[3H]aspartate and [14C]GABA without the help of any general depolarizing agent. Tetrodotoxin partially blocks the release of D-[3H]aspartate and completely blocks the induced release of [14C]GABA. Withdrawal of Ca2+ from the medium does not affect the D-[3H]aspartate release, but increases the extent of inhibition by tetrodotoxin. In contrast, removal of Ca2+ increases the cysteine sulfinic acid-induced [14C]GABA release, which remains totally blocked by the toxin. Anemonia sulcata toxin type II, which slows down Na+ channel inactivation, acts in synergism with cysteine sulfinic acid to increase the rate of release of both of the labeled amino acids. Comparison of glutamate with cysteine sulfinic acid in the same experiments indicates a different action pattern of the two acidic amino acids. Forskolin plus isobutyl methyl xanthine, which are known to raise intracellular cyclic adenosine monophosphate (cyclic AMP) levels, caused little release of the labeled amino acids on their own, but strongly enhanced the cysteine sulfinic acid-induced release. The experiments conducted by double labeling with D-[3H]aspartate and [14C]GABA, revealed several characteristic differences between the glutamatergic and the GABAergic neurons. It is tentatively concluded that cysteine sulfinic acid brings about excitation of the glutamatergic as well as the GABAergic neurons, leading to opening of Na+ channels which play a role in the release of both systems. Cyclic AMP, presumably by initiating phosphorylation of a specific component, has a remarkable potentiating effect on the release.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Ca-agonists: a new class of inotropic drugs.

The basic pharmacology of dihydropyridine Ca-agonists published so far (BAY k8644, CGP 28-392, H 160/51, YC 170, and 202-791) is described. The importance of the potency of the enantiomeres for the effect of a racemic compound is underlined. The Ca agonist prototype BAY k8644 leads to an increase of the maximal rate of rise of left ventricular pressure (LV(dP/dt)) and an increase of left ventricular stroke work in conscious dogs. When the vascular effects of BAY k8644 are counterbalanced by intravenous injection of sodium-nitroprusside, the left ventricular functions curves show markedly increased stroke work against the same mean arterial blood pressure at the same filling pressure. BAY k8644 stimulates the heart economically: the net efficiency in isolated working guinea-pig hearts is about 20%, identical to a stimulation by calcium or ouabain. Cardiotonic drugs acting via cAMP-dependent mechanisms like isoprenaline, amrinone, or pimobendane however, stimulate the heart about 1/3 less economically. The mechanism of action of Ca-agonists is explained from electrophysiological findings: Ca-agonistic dihydropyridines increase the open probability of the Ca-channels by a shift of the open-probability curve to more negative membrane potentials. As a consequence, the steady-state inactivation curve of the Ca-channel is also shifted in the same direction. While the effect on open-probability is the underlying mechanism for Ca-agonism, the latter effect results in Ca-antagonism. Therefore, depending on drug concentration and on membrane resting potential, a single chemical compound can act either as a Ca-agonist or a Ca-antagonist. A kinetic model of dihydropyridine action on the Ca-channel is described.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1988

Interaction of the beta-adrenergic receptor with Gs following delipidation. Specific lipid requirements for Gs activation and GTPase function.

Preparations of beta-adrenergic receptor and Gs from turkey erythrocytes were delipidated by previously developed procedures. Three synthetic phospholipids, dioleoylglycerophosphoethanolamine, dioleoylglycerophosphocholine and dioleoylglycerophosphoserine plus an unphosphorylated lipid, were all required to restore receptor-mediated activation of Gs by GTP[gamma S]. The same lipids were necessary for the reconstitution of the isoproterenol-enhanced GTPase. The requirement for the unphosphorylated lipid could be fulfilled by 1-mono-oleoyl glycerol, alpha-tocopherol or oleic acid. Cholesterol hemisuccinate further enhanced the receptor-mediated activity of the relipidated system when present in addition to the lipids specified above. Cholesterol hemisuccinate had no effect on the basal rate of Gs activation and depressed the basal GTPase. It is therefore suggested that cholesterol hemisuccinate affects the receptor or the coupling of the receptor to Gs. In the system relipidated with the three dioleoyl phospholipids, plus alpha-tocopherol and cholesterol hemisuccinate, the initial rate of Gs activation per mole receptor appeared to be considerably higher than in the native turkey erythrocyte membrane.

Animals↗
PubMed1988

Release of D-[3H]aspartate and [14C]GABA in rat hippocampus slices: effects of fatty acid-free bovine serum albumin and Ca2+ withdrawal.

Extended incubation of hippocampus slices in the presence of fatty acid-free bovine serum albumin (FAF-BSA) strongly enhanced the release of D-[3H]aspartate and [14C]GABA induced by veratridine. Saturation of the FAF-BSA with oleic acid abolished the enhancing effect. Spontaneous release and K+-induced release were not significantly changed by the addition of FAF-BSA. Amino-oxyacetic acid in the medium enhanced the veratridine-induced release of D-[3H] aspartate. The spontaneous release of [14C]GABA was greatly increased by Ca2+ withdrawal. With the further addition of EGTA the spontaneous release in the absence of Ca2+ increased more than 8-fold over the measured in the presence of 1.5 mM Ca2+. The enhanced release caused by Ca2+ withdrawal was totally blocked by tetrodotoxin. The toxin was effective even when added after the spontaneous release in the absence of Ca2+ was already proceeding at a high rate. The veratridine-induced release of [14C]GABA was also considerably augmented by Ca2+ withdrawal. D-[3H]aspartate release, studied simultaneously with [14C]GABA by double labeling, did not show enhanced spontaneous release upon Ca2+ withdrawal. The findings provide evidence that the enhanced [14C]GABA release caused by Ca2+ withdrawal is mediated by voltage-dependent Na+ channels.

Animals↗
PubMed1988

The distribution of potassium, sodium and chloride across the apical membrane of renal tubular cells: effect of acute metabolic alkalosis.

Studies were undertaken to define the effect of acute metabolic alkalosis (hypertonic sodium bicarbonate i.v.) on the chemical gradients for potassium, sodium and chloride across the apical membrane of individual renal tubule cells. Electron microprobe analysis was used on freeze-dried cryosections of the rat renal cortex to measure electrolyte concentrations in proximal tubule cells and in the various cell types of the superficial distal tubule. Analyses were also performed in fluid samples obtained by micropuncture from proximal and early and late distal collection sites. Compared with the appropriate controls (hypertonic sodium chloride i.v.), administration of sodium bicarbonate resulted only in small and mostly insignificant increases in cell potassium concentrations and induced only minor alterations in the cell/tubule fluid potassium concentration gradient for all cell types analysed. This observation suggests that under this condition factors other than an increase in cell potassium concentration are important in modulating potassium transfer across the apical membrane of potassium secreting cells. Nevertheless, since in alkalosis phosphorus and cell dry weight were decreased, and hence cell volume increased, in all but the intercalated cells, actually the potassium content of most tubular cells was higher under this condition. In comparison with animals infused with isotonic saline at low rates (hydropenic controls), infusion of either hypertonic sodium chloride or sodium bicarbonate led to a sharp increase in distal tubule fluid sodium concentrations and in the sodium concentrations of distal convoluted tubule, connecting tubule and principal cells, indicating that under both conditions the primary event causing enhanced transepithelial sodium absorption is stimulation of the sodium entry step.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkalosis↗
PubMed1988

Effect of acute metabolic acidosis on transmembrane electrolyte gradients in individual renal tubule cells.

We studied the effect of acute metabolic acidosis on potassium, sodium and chloride gradients across the apical membrane of proximal and distal tubule cells by determining electrolyte concentrations in individual cells and in tubule fluid employing electron microprobe analysis. Cellular measurements were performed on freeze-dried cryosections of the renal cortex, analysis of tubule fluid electrolyte concentrations on freeze-dried microdroplets of micropuncture samples obtained from proximal and from early and late distal collection sites. Acidosis (NH4Cl i.v. and i.g.) induced a substantial rise in plasma potassium concentration without significant effects on cell potassium concentrations. Potassium concentrations along the surface distal tubule were also unaltered; thus the chemical driving force for potassium exit from cell to lumen was not affected by acidosis. In all but intercalated cells acidosis markedly increased cell phosphorus concentration and cell dry weight indicating cell shrinkage and thus diminution of cell potassium content. Because the increase in intracellular chloride concentration exceeded the increase in plasma chloride concentration, the chemical chloride gradient across the contraluminal membrane was markedly depressed by acidosis.

Acidosis↗
PubMed1987

The four stereoisomers of a high potency congener of isoproterenol. Biological activity and the relationship between the native and the chemically inserted asymmetric carbon.

The RR isomer of a para-trifluoromethyl anilide congener of isoproterenol (PTFMA) had an affinity eighty and one hundred times higher than (-)isoproterenol for the beta receptor of turkey erythrocytes and of S49 cells respectively. This affinity was also much higher than that of +/- hydroxybenzyl isoproterenol (HBI) tested in the same experiments. The chemically inserted asymmetric carbon seemed to be as important as the native asymmetric carbon of the catecholamines in determining the binding affinity. Thus the RS and SR isomers demonstrated similar affinities in the turkey erythrocyte membranes as well as in the S49 lysed cells. The RR isomer had the lowest Kact in activation of adenylate cyclase in both beta receptor systems. The three most potent PTFMA isomers showed a Kact/Kd ratio which was higher than that of (-)isoproterenol or (+/-)HBI. It is therefore possible that the large substituent on the amino group in PTFMA, which greatly increases the binding affinity, is not as efficient in receptor activation. Yet the RR isomer had a Kact considerably lower than that of (-)isoproterenol in both of the beta receptor systems. The type of beta receptor of the turkey erythrocyte could be distinguished from that of the S49 cells by comparing the relative order of affinities of the RS and SR isomers and also by comparing (+/-)HBI with (-)isoproterenol. A labeled RR isomer of PTFMA could become most useful as an agonist ligand for beta receptors because of its very high binding affinity for both beta 1 and beta 2 receptors.

Adenylyl Cyclases↗
PubMed1987

Function of the delipidated beta-adrenergic receptor appears to require a fatty acid or a neutral lipid in addition to phospholipids.

Detergent-solubilized preparations of the beta-adrenergic receptor (R) and of the guanyl nucleotide binding proteins (Gs) were extensively treated to remove phospholipids and cholesterol. Reconstitution of an R-Gs system was subsequently performed in the presence of a mixture of natural phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine or the synthetic dioleoyl derivatives of the same phospholipids. In both cases, an additional lipid was required for the agonist-dependent activation of Gs. The requirement could be fulfilled by alpha-tocopherol, or by unsaturated fatty acids such as oleic acid. Inclusion of this non-phosphorylated lipid in the reconstituted system enhanced the isoproterenol-dependent activation of Gs by guanosine 5'-O-[gamma-thio]triphosphate 16-33-fold. The rate of activation was largely dependent on the addition of the agonist. Efficient functional reconstitution of R-Gs was thus achieved in a totally defined lipid system. Additional studies of the reconstituted system and of the native membrane led to the notion that the non-phosphorylated lipid plays a role in the function of the hormone-R complex.

Animals↗
PubMed1987

D-[3H]aspartate release from hippocampus slices studied in a multiwell system: controlling factors and postnatal development of release.

Medium components and various factors were tested to define optimal conditions for D-[3H]aspartate release. Isolation of the hippocampus and preparation of the slices in a medium without Ca2+ increased the release of D-[3H]aspartate in response to veratridine when subsequently tested in a regular Ca2+ containing medium. Apparently, the absence of Ca2+ during preparation of the slices reduced irreversible damage due to hypoxic conditions which prevail throughout the interval between killing the animal and immersion of the slices in a well oxygenated medium. Substitution of 10 mM Mg2+ for Ca2+ was an efficient procedure to test for Ca2+ dependence of D-[3H]aspartate release induced by veratridine. The inhibition was readily reversible when Ca2+ was readded. Veratridine (50 microM) was superior to high K+ (45 mM) in inducing D-[3H]aspartate release under all conditions tested in slices of mature animals. Furthermore, veratridine-induced release could be completely blocked by tetrodotoxin while K+-induced release was essentially unaffected by this toxin. Postnatal development of the D-[3H]aspartate release induced by veratridine was found to require 40-45 days, whereas release induced by K+ reached about 80% of maximum at postnatal day 22. K+-induced release appears to reach maturation when most hippocampal cells have been formed while veratridine-induced release probably requires completion of the neural circuit, involving also extensive sodium channel formation. These investigations were conveniently performed using a modified plastic culture box in which 24 slice systems can be studied simultaneously.

Animals↗