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Biomedical subjects

M Schramm

Publications and source records attributed to M Schramm.

At least 109 records · Page 6Linked to original sources
PubMed1983

Trapping of the beta-adrenergic receptor in the hormone-induced state.

Isoproterenol and other agonists readily dissociate from the beta-adrenergic receptor in turkey erythrocyte membranes. However, when a low concentration of deoxycholate is added, the receptor locks the prebound agonist; i.e., the rate of dissociation of the prebound agonist decreases drastically. The dissociation of prebound antagonists is slightly increased by deoxycholate. Locking, which is thus agonist specific, occurs in the cold, is reversed when detergent is removed from the membranes, and appears not to require the guanyl nucleotide binding protein of the adenylate cyclase system. It is suggested that this induced fit of a receptor to an agonist represents the specific conformational response that normally propagates in the receptor molecule in its interaction with the next component along the pathway of signal transmission.

Animals↗
PubMed1983

Impacted shoulders--a personal experience.

Failure of the shoulders to follow readily after delivery of the head is a life-threatening emergency for the mother and baby which is occasionally encountered by most obstetricians, and receives scant attention in current obstetric textbooks. This is a record of my personal experience of the condition, including 7 patients in whom a destructive procedure was required.

Delivery, Obstetric↗
PubMed1983

Activation of calcium channels by novel 1,4-dihydropyridines. A new mechanism for positive inotropics or smooth muscle stimulants.

The effects of the novel, 1,4-dihydropyridine derivative methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl) -pyridine-5-carboxylate (Bay k 8644) are reported. In contrast to the nifedipine-like dihydropyridines, which have calcium antagonistic actions. Bay k 8644 has positive inotropic and vasoconstrictor effects. The effects and mechanism of action of Bay k 8644 have been examined in the anaesthetised dog, on the isolated perfused guinea-pig heart, and on the isolated rabbit aortic strip. In these preparations Bay k 8644 is active in the same dose range as nifedipine, but has effects diametrically opposite to those of nifedipine. There is a competitive antagonism between Bay k 8644 and nifedipine, whereas verapamil and diltiazem produce only a functional, non-competitive inhibition of the effects of Bay k 8644. We conclude that a specific dihydropyridine receptor exists, which may bind both nifedipine and Bay k 8644. In contrast to nifedipine Bay k 8644 stimulates the calcium influx into the cell.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1983

Sodium and potassium concentrations of renal cortical cells two animal models of primary arterial hypertension.

Electron microprobe analysis was used to determine cellular concentrations of potassium and sodium in renal cortical cells of hypertensive rats of the Milan strain (MHS) and spontaneously hypertensive rats of the stroke prone strain (SHRSP) and their respective controls. Potassium concentrations in proximal and distal tubular cells were similar in both strains of hypertensive rats compared with their normotensive controls. In MHS rats proximal tubular cell sodium concentration was lower than in controls by 3.1 mmol/kg ww, whereas in both proximal and distal tubular cells of SHRSP sodium concentrations were higher than in controls by 5.3 and 4.3 mmol/kg ww, respectively. These results indicate that changes in the transport characteristics of the renal tubular epithelium are a feature of both models of hypertension.

Animals↗
PubMed1982

Probing of the coupling site of the beta-adrenergic receptor. Competition between different forms of the guanyl nucleotide binding protein for interaction with the receptor.

The interaction of the beta-adrenergic receptor (R) with different forms of the regulatory protein (G) was studied. For this purpose, the reconstituted system formed from separate soluble preparations of R and G was employed (Citri, Y., and Schramm, M. (1980) Nature (Lond.) 287, 297-300). Soluble preparations of the native nonactive G, to which GDP is bound (GGDP), and the persistently active G, to which guanyl-5'-yl-imidophosphate (Gpp(NH)p) is bound GGPP(MH)P), were prepared. Reconstituted systems made of GGDP, GGPP(NH)P, and R were used to test whether each of the two forms of G can affect the other's interaction with R. GGPP(NH)P was found to compete with GGDP for the interaction with R. However, GGDP was unable to interfere with the interaction of R with GGPP(NH)P. Similar experiments were carried out with another persistently active G (GGTP gamma S). In sharp contrast to GGPP(NH)P, GGTP gamma S was found incapable of competing with GGDP for R. The above experiments suggest that GGDP and GGPP(NH)P interact with the same coupling site on R. However, the degree of recognition of G by R depends strongly on the guanyl nucleotide which is bound to G. The relative order of recognition being GGPP(NH)P greater than GGDP greater than GGTP gamma S approximately 0. These findings may also explain the known irreversible effects of GTP gamma S in the adenylate cyclase system.

Adenylyl Cyclases↗
PubMed1982

Locking of hormone in the beta-adrenergic receptor by attack on a sulfhydryl in an associated component.

Isoproterenol incubated with turkey erythrocyte membranes causes exposure of a specific --SH in a component associated with the beta-adrenergic receptor, presumably in the guanyl nucleotide binding protein. Addition of a reagent which interacts with that specific --SH results in trapping of the hormone in the receptor. As a consequence, the number of hormone binding sites and the function of the receptor are both drastically reduced. Extended incubation at alkaline pH or addition of GDP or GTP at high concentration reactivate the beta-adrenergic receptor. Labeled antagonist binding as well as function of the receptor in activating an adenylate cyclase system are restored. The findings suggest that the normal interaction of the hormone-receptor complex with the guanyl nucleotide binding protein involves a conformational change which transiently locks the hormone in the receptor. GTP releases the tight interaction while addition of an --SH reagent traps the ternary complex of hormone-receptor-guanyl nucleotide binding protein in the locked conformation. Since the components of different hormone-activated adenylate cyclase systems were shown to be interchangeable, it seems likely that the hormone-receptor interaction with the guanyl nucleotide binding protein, as revealed in the present study, is not limited to beta-adrenergic receptor systems.

Animals↗
PubMed1980

Resolution, reconstitution and kinetics of the primary action of a hormone receptor.

The beta-adrenergic receptor (R) and the GTP binding protein (G) with which the receptor interacts were obtained in separate soluble fractions. Their recombination produced a hormone responsive system. In the presence of hormone the encounter of R with G in the reconstituted membrane occurs much faster than the subsequent R-induced activation of G.

Adenylyl Cyclases↗
PubMed1980

Functional implantation of a solubilized beta-adrenergic receptor in the membrane of a cell.

When the beta-adrenergic receptor of turkey erythrocytes was solubilized by deoxycholate, it retained its potential to activate an adenylate cyclase system. Electron microscopy showed that true solubilization had apparently been achieved; no residual membrane or vesicle structure was found. After removal of deoxycholate and addition of phospholipid, the reprecipitated beta-adrenergic receptor was implanted in the cell membrane of Friend erythroleukemia cells by using a chemical fusion method recently developed. Membranes prepared from the cells demonstrated 30-fold stimulation of the Friend cell adenylate cyclase by the implanted beta-adrenergic receptor. The function of the indigenous prostaglandin E(1) receptor of the Friend cells was not much affected by the implantation of large amounts of the foreign receptor. Activity mediated by the beta-adrenergic receptor reached 60% of the activity obtained with fluoride. The implanted receptor is therefore considered to be efficiently coupled to the adenylate cyclase system. The major difficulties hitherto preventing solubilization of hormone receptors and subsequent reconstitution of their function have been overcome by the approach developed in the present work. Conditions of solubilization need preserve only the receptor because all other components, even those unidentified as yet, can be supplied in excess by the adenylate cyclase system of the cell in which the receptor will be implanted. Subsequent recoupling of the receptor to the adenylate cyclase is performed in the native insoluble state of these molecules. Thus, the components need not be subjected to the hazards of solubilization in a common detergent as is usually required in reconstitution procedures. The importance of using implantation as an assay for a functional receptor in the course of purification and the likelihood that the procedure can be adapted to other receptors for hormones and neurotransmitters are discussed.

Adenylyl Cyclases↗
PubMed1979

Transfer of glucagon receptor from liver membranes to a foreign adenylate cyclase by a membrane fusion procedure.

Previous work had demonstrated the coupling of a beta-adrenergic receptor on an erythrocyte with the adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] of a tissue culture cell when the two cells were fused by Sendai virus. The validity of this finding for animal tissues in general, for membrane preparations, and for peptide hormone receptors could hitherto not be assessed. Available fusion procedures worked efficiently only with certain intact cells from tissue culture and with erythrocytes. In the present work a membrane fusion method was developed that causes the transfer of the glucagon receptor from purified rat liver membranes to Friend erythroleukemia cells; even direct transfer to a membrane fraction prepared from Friend cells became feasible. It can therefore be concluded that a peptide hormone receptor in a normal tissue membrane has properties similar to those demonstrated for a beta-adrenergic receptor in an erythrocyte: it exists in the membrane as a dissociable independent unit that can readily couple with the adenylate cyclase of a foreign cell. The efficiency of the membrane fusion procedure is due to the combined action of polyethylene glycol, phospholipids, stearylamine, and ATP in a salt medium. The method promises to be applicable to membranes of various cells and tissues, and it can probably be used to analyze hormone receptors and adenylate cyclase systems in states of malfunction by transfer to their respective counterpart in a normal cell membrane. Studies in biochemical hybridization of membrane components need not be limited to hormone activation of adenylate cyclase. With the aid of the membrane fusion method, this approach could be applied to any dissociable multicomponent system in biological membranes.

Adenylyl Cyclases↗