Biomedical subjects

Naoyuki Hayashi

Publications and source records attributed to Naoyuki Hayashi.

21 records · Page 2Linked to original sources

PubMed2003

The effect of muscle contraction velocity on cardiorespiratory responses to repetitive isokinetic exercise in humans.

We investigated the effect of muscle contraction velocity on cardiorespiratory responses during exercise. Eight males (23 +/- 2 years, 175 +/- 5 cm, 64 +/- 6 kg, mean +/- SD) performed 3-min repetitive one-leg extension exercises at various angular velocities (30, 60, 120, and 240 deg/s) with a controlled relaxation interval, relatively constant (duty cycle = 1:1, A trial) and absolutely constant (relaxation time = 0.75 s, B trial) at a total work of 2,100-2,400 J in an isokinetic mode, using a Cybex II dynamometer. We measured heart rate (HR), mean blood pressure (MAP), minute ventilation (Vdot;E), and oxygen uptake (Vdot;O(2)) during the exercise. The angular velocity significantly affected the increase in HR, MAP, Vdot;E, and Vdot;O(2) at the end of exercise from resting in both A and B trials (e.g., MAP: 12 +/- 2, 10 +/- 2, 11 +/- 2, and 18 +/- 2 mmHg in the A trial). The result suggests that muscle contraction velocity affects cardiorespiratory responses during repetitive isokinetic exercise.

Adult↗

PubMed2002

VO(2) kinetics in heavy exercise is not altered by prior exercise with a different muscle group.

We examined whether lactic acidemia-induced hyperemia at the onset of high-intensity leg exercise contributed to the speeding of pulmonary O(2) uptake (VO(2)) after prior heavy exercise of the same muscle group or a different muscle group (i.e., arm). Six healthy male subjects performed two protocols that consisted of two consecutive 6-min exercise bouts separated by a 6-min baseline at 0 W: 1) both bouts of heavy (work rate: 50% of lactate threshold to maximal VO(2)) leg cycling (L1-ex to L2-ex) and 2) heavy arm cranking followed by identical heavy leg cycling bout (A1-ex to A2-ex). Blood lactate concentrations before L1-ex, L2-ex, and A2-ex averaged 1.7 +/- 0.3, 5.6 +/- 0.9, and 6.7 +/- 1.4 meq/l, respectively. An "effective" time constant (tau) of VO(2) with the use of the monoexponential model in L2-ex (tau: 36.8 +/- 4.3 s) was significantly faster than that in L1-ex (tau: 52.3 +/- 8.2 s). Warm-up arm cranking did not facilitate the VO(2) kinetics for the following A2-ex [tau: 51.7 +/- 9.7 s]. The double-exponential model revealed no significant change of primary tau (phase II) VO(2) kinetics. Instead, the speeding seen in the effective tau during L2-ex was mainly due to a reduction of the VO(2) slow component. Near-infrared spectroscopy indicated that the degree of hyperemia in working leg muscles was significantly higher at the onset of L2-ex than A2-ex. In conclusion, facilitation of VO(2) kinetics during heavy exercise preceded by an intense warm-up exercise was caused principally by a reduction in the slow component, and it appears unlikely that this could be ascribed exclusively to systemic lactic acidosis.

Acidosis, Lactic↗

PubMed2001

Oligomeric interaction of hepatitis C virus NS5B is critical for catalytic activity of RNA-dependent RNA polymerase.

HCV NS5B is an RNA-dependent RNA polymerase (RdRP), a central catalytic enzyme for HCV replication, which has the "palm and fingers" substructure. We recently identified five novel residues critical for RdRP activity (Qin, W., Yamashita, T., Shirota, Y., Lin, Y., Wei, W., and Murakami, S. (2001) Hepatology 33, 728-737). Among them, GLU-18 and His-502, far from the catalytic center, may be involved in conformational change(s) for RdRP activity as addressed in some palm and fingers enzymes. We examined the possibility that NS5B is oligomerized, and we could detect the interaction between two different tagged NS5B proteins in vitro and transiently expressed in mammalian cells. By scanning 27 clustered and then point alanine substitutions in vivo and in vitro, Glu-18 and His-502 were found to be critical for the homomeric interaction in vivo and in vitro, strongly suggesting a close relationship between the oligomerization and RdRP activity of NS5B. All mutants with substitutions at these two residues failed to bind wild type NS5B, however E18H interacted with H502E in vitro and in vivo. Interestingly, the NS5B protein with E18H or H502E did not exhibit RdRP activity, but a mixture of the two mutant proteins did. These results clearly indicate that two residues of HCV NS5B are critical for the oligomerization that is prerequisite to RdRP activity.

Amino Acids↗