Biomedical subjects

Junichi Okada

Publications and source records attributed to Junichi Okada.

3 recordsLinked to original sources

PubMed2005

Polychlorinated biphenyl (PCB) alters acid-sensitivity of cultured neurons derived from the medulla oblongata.

Polychlorinated biphenyls (PCBs) are known as environmental pollutants that may cause adverse health problems. However, little is known about the effects of PCBs on acid-sensitive neurons of the medulla oblongata, which regulate respiration. Therefore, the present study was designed to examine whether PCB alters acid-sensitivity of cultured neurons derived from the rat medulla oblongata. When extracellular pH was shifted from 7.4 to 7.0, acid-sensitive neurons showed depolarization, which was measured by voltage-sensitive fluorescent dye. Exposure to PCB (Aroclor 1254) decreased the amplitude of depolarization in low pH and increased the resting membrane potential in a dose-dependent manner. Taken together, our results indicate that PCB potentially influences acid-sensitivity through alteration of the membrane potential of acid-sensitive neurons, which could affect the regulation of respiration.

Animals↗

PubMed2003

Graphical analysis of 99mTc thyroid scintigraphy.

A new non-invasive simple method for quantitative evaluation of thyroid was presented using graphical analysis of the transfer process of technetium-99m pertechnetate (99mTc) from the blood to thyroid. Thirty subjects were studied. After a bolus injection of 111 MBq of 99mTc, the data were recorded on a 128 x 128 matrix as 60 frames of 1.5-second duration. ROIs were placed over the aortic arch and bilateral thyroid lobes. The activity of the aorta was monitored instead of the arterial activity. Graphical analysis by plotting B(t)/A(t) versus integral(0)t A(tau)d tau/A(t) gave a straight line within the first 30 seconds in all subjects. The slope of the line was the unidirectional influx rate of 99mTc (k(u)). Thyroid perfusion index (TPI) was calculated to standardize where the ratio of ROI(thyroid) size to ROI(aorta) size was set as 10. K(u) and TPI showed good correlation with 99mTc thyroid uptake. Hyperthyroid patients showed high values of k(u) and TPI. Considering that these indices were determined at the first pass of 99mTc, this method may be helpful especially in the evaluation of thyroid perfusion.

Algorithms↗

PubMed2002

Past-A, a novel proton-associated sugar transporter, regulates glucose homeostasis in the brain.

The ventral medullary surface (VMS) of the medulla oblongata is known to be the site of the central chemosensitive neurons in mammals. These neurons sense excess H+/CO2 dissolved in the CSF and induce hyperventilation. To elucidate the mechanism of neuronal cell adaptation to changes of H+/CO2, we screened for hypercapnia-induced genes in the VMS. Here, we report cloning and characterization of a novel gene called proton-associated sugar transporter-A (Past-A), which is induced in the brain after hypercapnia and mediates glucose uptake along the pH gradient. Past-A comprises 751 amino acid residues containing 12 membrane-spanning helices, several conserved sugar transport motifs, three proline-rich regions, and leucine repeats. Past-A transcript was expressed predominantly in the brain. Moreover, the Past-A-immunoreactive neural cells were found in the VMS of the medulla oblongata, and the number of immunoreactive cells was increased by hypercapnic stimulation. Transient transfection of Past-A in COS-7 cells leads to the expression of a membrane-associated 82 kDa protein that possesses a glucose transport activity. The acidification of extracellular medium facilitated glucose uptake, whereas the addition of carbonyl cyanide m-chlorophenylhydrazone, a protonophore, inhibited glucose import. Together, our results indicate that Past-A is a brain-specific glucose transporter that may represent an adaptation mechanism regulating sugar homeostasis in neuronal cells after hypercapnia.

Administration, Inhalation↗