Biomedical subjects

H Oka

Publications and source records attributed to H Oka.

At least 577 records · Page 32Linked to original sources

PubMed1975

Subfractionation of rat liver plasma membrane. Uneven distribution of plasma membrane-bound enzymes on the liver cell surface.

Plasma membranes were isolated from rat liver mainly under isotonic conditions. As marker enzymes for the plasma membrane, 5'-nucleotidase and (Na+ + K+)-ATPase were used. The yield of plasma membrane was 0.6-0.9 mg protein per g wet weight of liver. The recovery of 5'-nucleotidase and (Na+ +K+)-ATPase activity was 18 and 48% of the total activity of the whole-liver homogenate, respectively. Judged from the activity of glucose-6-phosphatase and succinate dehydrogenase in the plasma membrane, and from the electron microscopic observation of it, the contamination by microsomes and mitochondria was very low. A further homogenization of the plasma membrane yielded two fractions, the light and heavy fractions, in a discontinuous sucrose gradient centrifugation. The light fraction showed higher specific activities of 5'-nucleotidase, alkaline phosphatase, (Na+ +K+)-ATPase and Mg2+-ATPase, whereas the heavy one showed a higher specific activity of adenylate cyclase. Ligation of the bile duct for 48 h decreased the specific activities of (Na2+ +K+)-ATPase and Mg2+-ATPase in the light fraction, whereas it had no significant influence on the activities of these enzymes in the heavy fraction. The specific activity of alkaline phosphate was elevated in both fractions by the obstruction of the bile flow. Electron microscopy on sections of the plasma membrane subfractions showed that the light fraction consisted of vesicles of various sizes and that the heavy fractions contained membrane sheets and paired membrane strips connected by junctional complexes, as well as vesicles. The origin of these two fractions is discussed and it is suggested that the light fraction was derived from the bile front of the liver cell surface and the heavy one contained the blood front and the lateral surface of it.

Adenosine Triphosphatases↗

PubMed1975

Responses of pontocerebellar neurones to stimulation of the parietal association and the frontal motor cortices.

The corticopontine projections from the parietal association cortex (the anterior portion of the middle suprasylvian gyrus) were electrophysiologically investigated and compared with those from the frontal motor cortex (the anterior sigmoid gyrus) in cats under light Nembutal anaesthesia. It was indicated by field potential study that the pontine nucleus (PN) neurones receive a significant amount of the direct corticopontine fibres from both the parietal and frontal cortical areas. In extracellular unitary study, out of 107 PN neurones identified by antidromic activation due to the brachium pontis stimulation, 33 responded with firings to stimulation of the parietal association area and 64 to the frontal motor area. Only 10 of them were excited by both parietal and frontal stimulations, but they were not estimated to receive the dual monosynaptic projections from both cortical areas. There were found data suggesting that the pontocerebellar neurones with faster conduction velocities respond at shorter latencies to the cortical stimulation and those with slower conduction velocities fire at longer latencies on the cortical stimulation. No remarkable difference was observed between the topographical localization of the PN neurones receiving the projection fibres from the parietal association and the frontal motor cortical areas. It was concluded that a vast majority of the pontocerebellar neurones possibly receive monosynaptic contacts differentially with the corticopontine fibres originating from the parietal association and the frontal motor areas.

Animals↗

PubMed1975

Electrophysiological studies of the projections from the parietal association area to the cerebellar cortex.

1. Responses evoked in the cerebellar cortex by stimulation of the parietal association cortex (rostral portions of the middle suprasylvian gyrus) were recorded and analysed in cats, and were compared with those by stimulation of the motor cortex (anterior sigmoid gyrus). 2. The parietal stimulation elicited early mossy fibre and late climbing fibre responses in the cerebellar cortex. The mossy fibre responses appeared at a latency of 2.0--2.5 msec and predominantly in the lateral (hemispherical) part of the contralateral cerebellum (mainly crus I, crus II and paramedian lobules). Cutting of the inferior cerebellar peduncle produced little or no influence upon the mossy fibre responses, which suggests that the mossy fibre responses are mediated chiefly by the pontine nuclei. 3. The climbing fibre responses were recorded at a latency of 17--19 msec and markedly in the contralateral intermediate and medial parts of IV--VI lobules. The responses were easily sppressed by anaesthesia and depended on the conditions of experimental animals. The unstable appearance of the responses and their longer latencies than those of the climbing fibre responses due to stimulation of the motor cortex imply indirect pathways from the parietal association cortex to the inferior olive. 4. The predominant projection of the parietal-induced mossy fibre responses to the lateral part of the cerebellum was compared with the mossy fibre projection from the motor cortex and was discussed as an important component in the cerebrocerebellar loops.

Animals↗

PubMed1975

Thalamo-cortical projections for recruiting responses and spindling-like responses in the parietal cortex.

1. The thalamic neurones sending their axons to the parietal association cortex (middle suprasylvian gyrus) and receiving monosynaptic excitation from the cerebellar (interpositus or lateral) nucleus were recorded with microelectrodes extracellularly and intracellularly around the anterior ventral (VA) nucleus of the thalamus in cats. Such thalamic neurones are known to carry exclusively the impulses responsible for superficial thalamo-cortical (T-C) responses in the parietal cortex, being called superficial T-C neurones (see Sasaki et al., 1972a, b). 2. Repetitive (6--9/sec) stimulation of the centrum medianum-parafascicular complex (CM) or the intralaminar nuclei (IL) of the thalamus elicited grouped spike discharges of the neurone in synchronization with the recruiting responses in the parietal cortex. The grouped discharges usually preceded the respective cortical responses by several milliseconds. Numbers of the spikes in the grouped discharges increased and decreased as the recruiting responses waxed and waned on the repetitive stimulation. 3. The superficial T-C neurones also showed similar grouped discharges in synchronization with spindling-like, surface-negative cortical responses which occurred spontaneously or were evoked by single thalamic stimulation. 4. It was concluded that the superficial T-C neurons can convey impulses for recruiting responses and spindling-like responses from the thalamus directly to the cerebral cortex. They are supposed to constitute the final T-C pathway of the neuronal circuits of the recruiting system, i.e., non-specific T-C projection system.

Animals↗

PubMed1975

Demonstration of C-peptide immunoreactivity in various body fluids and clinical evaluation of the determination of urinary C-peptide immunoreactivity.

C-peptide immunoreactivity (CPR) was demonstrated not only in plasma, but in urine, ascites, cerebrospinal fluid and pleural effusion. The concentration of CPR in urine was very high compared with that in the other body fluids and was easy to assay. CPR in urine after glucose administration or tolbutamide injection increased parallel to the change of CPR in plasma and also to that of IRI in normals or diabetics without renal disturbances. The result suggest that the determination of CPR in urine before and after stimulation of insulin secretion could serve as a simple indicator of insulin secretory function of pancreas.

Adult↗

PubMed1975

Effects of calcium ionophore (A-23187) on glucose oxidation and iodide transport in dog thyroid slices.

A calcium ionophore (A-23187, 20 mug/ml) stimulted 14C-1-glucose oxidation in dog thyroid slices to an extent equivalent to that obtained by the optimal concentration of dibutyryl cyclic AMP (1mM). Furthermore, the ionophore augmented the stimulation by dibutyryl cyclic AMP much more than the simple additive effect. The ionophore also enhanced the effect of TSH, but to a lesser extent. Under conditions where organic binding was blocked, T/M ratio of radioiodine concentration was lowered in slices by the ionophore; the findings similar to those obtained with TSH and dibutyryl cyclic AMP. The ionophore exhibited a slightly depressive effect on the basal cyclic AMP level. The elevation by TSH of cyclic AMP levels was also slightly depressed by the ionophore, but statistically insignificant in most cases. These results indicate that calcium ion may play an important role in the TSH regulation of iodide transport and glucose metabolism in the thyroid, in some cases by augmenting the effects of cyclic AMP.

Animals↗

PubMed1975

Effect of glucose on adenosine 3', 5'-monophosphate levels in rat pancreatic islets.

Time course of the changes in insulin release and cyclic AMP levels in isolated rat islets incubated in media containing 5 or 16.7 mM of glucose were followed. The higher glucose concentration caused a slight but significant increase of cyclic AMP levels after 10 min incubation, but not 5 min incubation, whereas the stimulation of insulin release by 16.7 mM of glucose was apparent in both incubation times. Theophylline increased cyclic AMP levels markedly but did not stimulate insulin release when the glucose concentration was 5 mM. A slight augmentation by theophylline of insulin release was observed in the incubation medium containing 16.7 mM glucose. All these findings suggest that the elevation of cyclic AMP in islets may not play a role for the initiation of the insulin release induced by glucose, though it may act to modulate the glucose effect.

Animals↗

PubMed1975