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Biomedical subjects

B Rossi

Publications and source records attributed to B Rossi.

At least 199 records · Page 11Linked to original sources
PubMed1985

The role of the tactile-pressure afferents in the habituation phenomenon of trigemino-facial reflex.

In ten healthy subjects the trigemino-facial reflex was elicited by double shock (delta t = 0.5-1 s). The first stimulus was subliminal for pain and the second supramaximal for it. The percentage integral values, with respect to single shock, of the direct and consensual conditioned responses obtained in all subjects were averaged and compared with those conditioned by supramaximal stimuli for pain fibres. Significant differences between subliminal and supramaximal conditioning stimuli for pain fibres is revealed for only consensual R3 with delta t = 1 s: greater inhibition with painful stimuli. There were no significant differences in any of the other values. Our results show that a subliminal conditioning stimulus for pain threshold can inhibit the late responses to the test stimulus, both for R2 and especially for R3, suggesting that this mechanism can contribute to the trigemino-facial reflex habituation phenomenon.

Electrophysiology↗
PubMed1985

Influences of neck vibration on lower limb extensor muscles in man.

The effects of neck vibration were studied in ten healthy subjects standing in unrestrained or restrained conditions. An involuntary slow and gradual displacement of the body axis associated with a subjective experience of forward tilt occurred during vibration of the dorsal surface of the neck. This effect was associated with a decreased tonic contration of the antigravitary lower limb musculature. The amplitude of the H-reflex from the soleus muscle, recorded at progressively increasing time interval after the onset of the vibratory stimulus, showed complex interactions: in particular, in unrestrained conditions an early inhibitory phase occurred at about 100 msec, followed by a short-lasting facilitatory phase between 150-300 msec and by a late long-lasting excitatory component which started 500-600 msec after the onset of vibratory stimulus. In restrained subjects, the late excitatory phase disappeared and was substituted by a delayed depression. In this instance, the short-lasting facilitatory phase appeared to be superimposed on a background of inhibition. The effects produced by the neck input on the H-reflex were attenuated during vibration of the dorsal muscolature at L4-L5. The mechanisms involved in the cervical control of posture and reflex movements following neck vibration are discussed.

Adult↗
PubMed1984

Antibodies against the plasma membrane 3,3',5-triiodo-L-thyronine binding protein of rat pituitary GH3 cells: partial characterization and cross-species immunoreactivity.

To develop antibodies against the plasma membrane 3,3',5-triiodo-L-thyronine (T3) binding protein (M.W. 55,000), rabbits were immunized with formalin-fixed GH3 cells or highly purified plasma membranes from these cells. Antibodies were screened by immunoprecipitation using detergent solubilized N-bromoacetyl-[125I]T3-labeled 55K protein. Among the nine detergents tested, 0.18% CHAPS was found to be the best in its solubilization efficiency and its ability to maintain the integrity of the antigenicity of the 55K protein. The N-bromoacetyl-[125I]T3-labeled 55K protein was also immunoprecipitated by anti-T3 antibodies. The anti-55K protein antibodies cross-reacted with plasma membrane T3 binding proteins from cultured cells and tissues of human and rodent origin. These results indicate that structural similarities exist in human and rodent plasma membrane T3 binding proteins. These antibodies should provide a powerful tool in the characterization and in probing the function(s) of the plasma membrane T3 binding protein in cells.

Animals↗
PubMed1984

A search for an 'ouabain-like' substance from the electric organ of Electrophorus electricus which led to arachidonic acid and related fatty acids.

The electric organ of Electrophorus electricus contains substances which inhibit (Na+ + K+)-ATPase activity, the specific binding of [3H]ouabain to purified (Na+ + K+)-ATPase and 86Rb+ uptake by chick cardiac cells in culture. The active organic material was extracted from microsomal membranes. Its purification was carried out by chromatography on Sep-Pak C-18 and thin-layer chromatography. Reverse-phase liquid chromatography and mass spectrometry identified the active material as a mixture of unsaturated fatty acids. Linoleic (18:2), arachidonic (20:4), linolenic (18:3) and docosahexaenoic acids (22:6) contributed to about 60% of the total activity of the active material. The other active substances could be arachidonic analogs, since they have both a lipophilic and carboxylic character. Pure unsaturated fatty acids have been shown to be active in the different biological assays used to analyze the endogenous 'ouabain-like' activity. Linolenic, arachidonic and docosahexaenoic acids were the most active, whereas saturated fatty acids and glyceryl esters or methyl esters of unsaturated fatty acids were inactive. It is possible that in pathological situations in which the level of unsaturated fatty acids increases, these molecules may then act as physiological inhibitors of the sodium pump.

Animals↗
PubMed1984

Digitalis receptors affinity labelling and relation with positive inotropic and cardiotoxic effects.

Affinity labelling of the digitalis receptor has indicated that it is situated on the N-terminal part of the alpha-subunit of the (Na+,K+)ATPase. Biochemical and pharmacological properties of the (Na+,K+)ATPase studied on intact chick embryonic hearts and under heart cell culture conditions have indicated the existence of two families of ouabain binding sites i.e.: a low affinity binding sites with a dissociation constant (Kd) of 2-6 microM for the ouabain-receptor complex and a high affinity binding site with a Kd of 26-48 nM. High and low affinity sites also are present at all embryonic stages studied. Inhibition of 86Rb+ uptake in cultured cardiac cells and increase in intracellular Na+ concentration, due to (Na+,K+)ATPase blockade, occur in an ouabain concentration range corresponding to the saturation of the low affinity ouabain site. Ouabain stimulated 45Ca2+ uptake increases in parallel with the increase in the intracellular Na+ concentration. It is suppressed in Na+ free medium or when Na+ is replaced by Li+ suggesting that the increase is due to the indirect activation of the Na+/Ca2+ exchange system in the plasma membrane. Dose-response curves for the inotropic effects of ouabain on papillary muscle and on ventricular cells in culture indicate the development of the cardiotonic properties is parallel to the saturation of the low affinity binding site for ouabain. Therefore, inhibition of the cardiac (Na+,K+)ATPase corresponding to low affinity ouabain binding sites seems to be responsible for both the cardiotonic and cardiotoxic effects of the drug.

Affinity Labels↗
PubMed1984

Repetitive nerve stimulation in the differential diagnosis of congenital myotonia.

Repetitive stimulation of the ulnar nerve at 5 Hz was performed in 9 patients with congenital myotonia, 3 with dominant and 6 with recessive transmission. At this frequency the motor response differed markedly, all the patients with the recessive form presenting a clear decremental response to repeated stimulation. The size and time course of the decrease seem to be related to the degree of muscular paresis. The series includes one case of dominant congenital myotonia type II, whose response to repetitive stimulation, reported for the first time, did not differ from that of the other cases with the classic Thomsen form. Electromyography would thus seem to be a sure means of differentiating recessive from dominant forms of congenital myotonia in sporadic cases.

Adolescent↗
PubMed1984

R1 responses of the trigeminofacial reflex in lesions extrinsic to the brain stem.

Isolated or prevalent impairment of the trigeminofacial reflex (tfr) has been described both in pontine lesions and in lesions extrinsic to the brain stem. No satisfactory explanation of this finding in extrinsic lesions has ever been put forward. In a series of patients with lesions outside the brain stem together with selective or prevalent R1 impairment reported here this finding can be explained by the peculiar anatomy of the various nerve fibers in the trigeminal sensory root.

Adult↗
PubMed1984

Digitalis receptors in cardiac cells and their relation with positive inotropic and cardiotoxic effects.

Biochemical and pharmacological properties of (Na+,K+)ATPase have been studied on intact chick embryonic hearts and under heart cell culture conditions. The results show the existence of two families of ouabain binding sites: a low affinity binding site with a dissociation constant (Kd) of 2-6 microM for the ouabain-receptor complex and a high affinity binding site with a Kd of 26-48 nM. High and low affinity sites are also present at all embryonic stages studied. Inhibition of 86Rb+ uptake in cultured cardiac cells and increase in intracellular Na+ concentration, due to (Na+,K+)ATPase blockade, occur in a ouabain concentration range corresponding to the saturation of the low affinity ouabain site. Ouabain stimulated 45Ca2+ uptake increases in parallel with the increase in the intracellular Na+ concentration. It is suppressed in Na+ free medium or when Na+ is replaced by Li+ suggesting that the increase is due to the indirect activation of the Na+/Ca2+ exchange system in the plasma membrane. Dose-response curves for the inotropic effects of ouabain on papillary muscle and on ventricular cells in culture indicate that the development of the cardiotonic properties is parallel to the saturation of the low affinity binding site for ouabain. Therefore, inhibition of the cardiac (Na+,K+)ATPase corresponding to low affinity ouabain binding sites seems to be responsible for both the cardiotonic and cardiotoxic effects of the drug.

Animals↗
PubMed1983

Two classes of ouabain receptors in chick ventricular cardiac cells and their relation to (Na+,K+)-ATPase inhibition, intracellular Na+ accumulation, Ca2+ influx, and cardiotonic effect.

The biochemical and pharmacological properties of the (Na+,K+)-ATPase have been studied at different stages of chick embryonic heart development in ovo and under cell culture conditions. The results show the existence of two families of ouabain binding sites: a low affinity binding site with a dissociation constant (Kd) of 2-6 microM for the ouabain-receptor complex and a high affinity binding site with a Kd of 26-48 nM. Levels of high affinity sites gradually decrease during cardiac ontogenesis to reach a plateau near 14 days of development. Conversely the number of low affinity binding sites is essentially invariant between 5 days and hatching. Cultured cardiac cells display the same binding characteristics as those found in intact ventricles. Inhibition of 86Rb+ uptake in cultured cardiac cells and an increase in intracellular Na+ concentration, due to (Na+,K+)-ATPase blockade, occur in a ouabain concentration range corresponding to the saturation of the low affinity ouabain site. Ouabain-stimulated 45Ca2+ uptake increases in parallel with the increase in the intracellular Na+ concentration. It is suppressed in Na+-free medium or when Na+ is replaced by Li+ suggesting that the increase is due to the indirect activation of the Na+/Ca2+ exchange system in the plasma membrane. Dose-response curves for the inotropic effects of ouabain on papillary muscle and on ventricular cells in culture indicate that the development of the cardiotonic properties is parallel to the saturation of the low affinity binding site for ouabain. Therefore, inhibition of the cardiac (Na+,K+)-ATPase corresponding to low affinity ouabain binding sites seems to be responsible for both the cardiotonic and cardiotoxic effects of the drug.

Animals↗
PubMed1983

Characterization of ouabain-resistant mutants of a canine kidney cell line, MDCK.

Madin-Darby canine kidney (MDCK) cells were mutagenized and variants resistant to 10, 160, and 2000 times the ouabain lethal dose for wild type cells selected. The phenotypes were stable in the absence of selection. The frequencies with which variants were recovered were consistent with genetic alterations being responsible for drug resistance. It was shown that 50% of the (Na+, K+)-ATPase activity present in mutant cells had a higher Kd for ouabain than normal while 50% remained wild type for ouabain binding. Wild type MDCK cells were measured to have 2 X 10(6) ouabain binding sites per cell with a Kd for the drug of 0.6-1.0 X 10(-7) M. The novel (Na+, K+)-ATPase activities in the mutants demonstrated Kd values for ouabain of 10(-5) M, 3 X 10(-4) M, or 3 X 10(-3) M for the different mutant classes tested. The rate of synthesis of the (Na+, K+)-ATPase as well as the total amount of enzyme per unit of cell protein was unaltered in the mutants. Comparison of the alpha subunit of the enzyme, known to contain the ouabain-binding site, by sodium dodecyl sulfate-gel electrophoresis did not reveal any difference in the size of this subunit in mutant versus wild type cells.

Animals↗
PubMed1983

Specific photoaffinity labeling of the digitalis binding site of the sodium and potassium ion activated adenosinetriphosphatase induced by energy transfer.

A ouabain p-aminobenzenediazonium derivative with a high specific radioactivity has been synthesized from ouabain and used as a photolabel for the (sodium plus potassium)-activated adenosinetriphosphatase from Electrophorus electricus electric organ and from dog kidney. In the dark it binds reversibly to the digitalis receptor site, with binding characteristics comparable to those of ouabain. The photoactivation of the ouabain derivative to produced covalent labeling of the receptor was obtained by energy transfer from a tryptophan residue in the (Na+,K+)ATPase to the ouabain p-aminobenzenediazonium molecule bound at the active site. The great advantage of this procedure compared to previous methods is that free molecules of the photoactivatable derivative are not photodecomposed. Analysis of the photolabeled polypeptides on sodium dodecyl sulfate gel electrophoresis showed that over 90% of the total radioactivity incorporated was found in the large molecular weight alpha-chain of the kidney enzyme (Mr 93 000). The same specific labeling of the alpha-subunit was obtained with a crude microsomal fraction from Electrophorus electricus. A mild tryptic fragmentation of the subunit into two peptide fragments of Mr 58 000 and 41 000, respectively, shows that the digitalis receptor is located in the N-terminal 41 000 fragment.

Affinity Labels↗
PubMed1983

Affinity labeling and localization of the ATP binding site in the (Na+,K+)-ATPase.

The (Na+,K+)-ATPase has been covalently labeled with oxidized ATP. The extent of oxidized ATP incorporation which inactivates the enzyme corresponds to one nucleotide site per equivalent of ouabain binding site. ATP and ADP protect against the covalent labeling by oxidized ATP; the dissociation constants for the protective effects of ATP and ADP are 0.6 mM and 2.5 mM, respectively. The covalent incorporation is accelerated by K+ and by ouabain in the presence of Mg2+. The site of incorporation of oxidized ATP is located on a Mr = 58,000 fragment situated at the COOH-terminal end of the Mr = 94,000 alpha chain, while the phosphorylation site and the ouabain site are in the other (NH2-terminal) part of the chain.

Adenosine Triphosphate↗