Biomedical subjects

Hirofumi Nakamura

Publications and source records attributed to Hirofumi Nakamura.

3 recordsLinked to original sources

PubMed2006

Pathophysiological basis for monitoring of whole heart conductance by 2-lead system.

BACKGROUND: The defibrillation threshold (DFT) is elevated during myocardial ischemia, but the underlying mechanism remains to be elucidated. The hypothesis tested by the present study was that whole heart conductance (WHC) is a determinant of DFT. METHODS AND RESULTS: WHC was monitored across the longest diameter of the isolated perfused rat heart, using a 2-electrode instrument under various conditions including ischemia-reperfusion (IR). In the control study, WHC was influenced by the conductivity and flow rate of the solution. In IR, WHC decreased immediately after the onset of perfusion arrest in a single exponential manner, then declined again gradually. The second decrease was augmented and accelerated by pretreatment with 1.0 mmol/L heptanol (p<0.005) or high-[Ca2+]e (p<0.001), and was attenuated and delayed by pretreatment with 1.0 micromol/L verapamil (p<0.01). WHC after reperfusion was greater than the pre ischemic level. The postischemic increase in WHC was proportional to the ischemic interval and tissue water content as assessed by desiccation method. CONCLUSION: Although time-dependent alterations in DFT in ischemic hearts may be attributable at least in part to dynamic changes in WHC, WHC should be interpreted carefully because it reflects many physiological factors such as coronary perfusion, electrical coupling of cardiac myocytes and tissue edema.

Animals↗

PubMed2005

Emphysematous cystitis with venous bubbles.

An 86-year-old nondiabetic woman with an episode of transient ischemic attack two days earlier was referred to our hospital. She had a history of neurogenic bladder and chronic atrial fibrillation and had been anuric for two days. Bubbles were detected by echocardiography in the right atrium, right ventricle, and inferior vena cava. Computed tomography revealed gas accumulation in the wall and lumen of the bladder. She recovered after urinary drainage and antibiotic therapy, and bubbles were no longer detected. It was suspected that bacterial injury of the bladder wall and high intravesical pressure led gas to enter the venous system.

Aged↗

PubMed2002

In vitro evolution of a polyhydroxybutyrate synthase by intragenic suppression-type mutagenesis.

In vitro evolution was applied to obtain highly active mutants of Ralstonia eutropha polyester synthase (PhbC(Re)), which is a key enzyme catalyzing the formation of polyhydroxybutyrate (PHB) from (R)-3-hydroxybutyryl-CoA (3HB-CoA). To search for beneficial mutations for activity improvement of this enzyme, we have conducted multi-step mutations, including activity loss and intragenic suppression-type activity reversion. Among 259 revertants, triple mutant E11S12 was obtained as the most active one via PCR-mediated secondary mutagenesis from mutant E11 with a single mutation (Ser to Pro at position 80), which exhibited reduced activity (as low as 27% of the wild-type level) but higher thermostability compared to the wild-type enzyme. Mutant E11S12 exhibited up to 79% of the wild-type enzyme activity. Mutation separation of E11S12 revealed that the replacement of Phe by Ser at position 420 (F420S), located in a highly conserved alpha/beta hydrolase fold region, of the E11S12 mutant contributes to the improvement of the enzyme activity. A purified sample of the genetically engineered mutant, termed E11S12-1, with the F420S mutation alone was found to exhibit a 2.4-fold increase in specific activity toward 3HB-CoA, compared to the wild-type.

Acyltransferases↗