Biomedical subjects

Mitsuo Mita

Publications and source records attributed to Mitsuo Mita.

5 recordsLinked to original sources

PubMed2006

Algorithm for the classification of multi-modulating signals on the electrocardiogram.

This article discusses the algorithm to measure electrocardiogram (ECG) and respiration simultaneously and to have the diagnostic potentiality for sleep apnoea from ECG recordings. The algorithm is composed by the combination with the three particular scale transform of a(j)(t), u(j)(t), o(j)(a(j)) and the statistical Fourier transform (SFT). Time and magnitude scale transforms of a(j)(t), u(j)(t) change the source into the periodic signal and tau(j) = o(j)(a(j)) confines its harmonics into a few instantaneous components at tau(j) being a common instant on two scales between t and tau(j). As a result, the multi-modulating source is decomposed by the SFT and is reconstructed into ECG, respiration and the other signals by inverse transform. The algorithm is expected to get the partial ventilation and the heart rate variability from scale transforms among a(j)(t), a(j+1)(t) and u(j+1)(t) joining with each modulation. The algorithm has a high potentiality of the clinical checkup for the diagnosis of sleep apnoea from ECG recordings.

Algorithms↗

PubMed2005

Augmentation of alpha1-adrenoceptor-mediated contraction by warming without increased phosphorylation of myosin in rat caudal arterial smooth muscle.

We previously reported the relationship between alpha1-adrenoceptor-mediated contraction and phosphorylation of 20-kDa myosin light chain (LC20) in de-endothelialized rat caudal arterial smooth muscle at room temperature (Mita M, Walsh MP. Biochem J. 1997;327:669-674). We now describe the effect of increasing the temperature to 37 degrees C on this relationship. The EC50 value (76.6 +/- 18.2 nM) for cirazoline (alpha1-adrenergic agonist)-induced contraction of the strips at room temperature (23 degrees C) was significantly greater than that (14.5 +/- 1.9 nM) at 37 degrees C. The initial rate of the contraction to a sub-maximal concentration of cirazoline (0.3 microM) was similar at the two temperatures. However, cirazoline-induced maximal force at 37 degrees C was approximately 1.8 times that at room temperature. LC20 phosphorylation in response to cirazoline at room temperature and 37 degrees C closely matched the time courses of contraction, but values were not significantly different at the two temperatures: resting phosphorylation levels were 0.09 +/- 0.04 mol P(i)/mol LC20 at 37 degrees C and 0.22 +/- 0.06 mol P(i)/mol LC20 at room temperature; maximal cirazoline-stimulated LC20 phosphorylation levels were 0.58 +/- 0.08 mol P(i)/mol LC20 at room temperature and 0.49 +/- 0.05 mol P(i)/mol LC20 at 37 degrees C. We conclude, therefore, that the enhanced cirazoline-induced contraction at 37 degrees C is not due to increased LC20 phosphorylation.

Adrenergic alpha-Agonists↗

PubMed2003

The role of RhoA and Rho-associated kinase in vascular smooth muscle contraction.

A variety of contractile agonists trigger activation of the small GTPase RhoA. An important target of activated RhoA in smooth muscle is Rho-associated kinase (ROK), one of the downstream targets that is the myosin binding subunit (MYPT1) of myosin light chain phosphatase (MLCP). Phosphorylation of MYPT1 at T695 by activated ROK results in a decrease in phosphatase activity of MLCP and an increase in myosin light chain (LC(20)) phosphorylation catalyzed by Ca(2)(+)/calmodulin-dependent myosin light chain kinase and/or a distinct Ca(2)(+)-independent kinase. LC(20) phosphorylation in turn triggers cross-bridge cycling and force development. ROK also phosphorylates the cytosolic protein CPI-17 (at T38), which thereby becomes a potent inhibitor of MLCP. The RhoA/ROK pathway has been implicated in the tonic phase of force maintenance in response to various agonists, with no evident role in the phasic response, suggesting this pathway as a potential target for antihypertensive therapy. Indeed, ROK inhibitors restore normal blood pressure in several rat hypertensive models.

Animals↗

PubMed2002

Membrane depolarization-induced contraction of rat caudal arterial smooth muscle involves Rho-associated kinase.

Depolarization of the sarcolemma of smooth muscle cells activates voltage-gated Ca2+ channels, influx of Ca2+ and activation of cross-bridge cycling by phosphorylation of myosin catalysed by Ca2+/calmodulin-dependent myosin light-chain kinase (MLCK). Agonist stimulation of smooth muscle contraction often involves other kinases in addition to MLCK. In the present study, we address the hypothesis that membrane depolarization-induced contraction of rat caudal arterial smooth muscle may involve activation of Rho-associated kinase (ROK). Addition of 60 mM K+ to de-endothelialized muscle strips in the presence of prazosin and propranolol induced a contraction that peaked rapidly and then declined to a steady level of force corresponding to approx. 30% of the peak contraction. This contractile response was abolished by the Ca2+-channel blocker nicardipine or the removal of extracellular Ca2+. An MLCK inhibitor (ML-9) inhibited both the phasic and tonic components of K+-induced contraction. On the other hand, the ROK inhibitors Y-27632 and HA-1077 abolished the tonic component of K+-induced contraction, and slightly reduced the phasic component. Phosphorylation levels of the 20-kDa light chain of myosin increased rapidly in response to 60 mM K+ and subsequently declined to a steady-state level significantly greater than the resting level. Y-27632 abolished the sustained and reduced the phasic elevation of the phosphorylation of the 20-kDa light chain of myosin, without affecting the K+-induced elevation of cytosolic free Ca2+ concentration. These results indicate that ROK activation plays an important role in the sustained phase of K+-induced contraction of rat caudal arterial smooth muscle, but has little involvement in the phasic component of K+-induced contraction. Furthermore, these results are consistent with inhibition of myosin light-chain phosphatase by ROK, which would account for the sustained elevation of myosin phosphorylation and tension in response to membrane depolarization.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed2002

Cloning and characterization of novel snake venom proteins that block smooth muscle contraction.

In this study, we isolated a 25-kDa novel snake venom protein, designated ablomin, from the venom of the Japanese Mamushi snake (Agkistrodon blomhoffi). The amino-acid sequence of this protein was determined by peptide sequencing and cDNA cloning. The deduced sequence showed high similarity to helothermine from the Mexican beaded lizard (Heloderma horridum horridum), which blocks voltage-gated calcium and potassium channels, and ryanodine receptors. Ablomin blocked contraction of rat tail arterial smooth muscle elicited by high K+-induced depolarization in the 0.1-1 microm range, but did not block caffeine-stimulated contraction. Furthermore, we isolated three other proteins from snake venoms that are homologous to ablomin and cloned the corresponding cDNAs. Two of these homologous proteins, triflin and latisemin, also inhibited high K+-induced contraction of the artery. These results indicate that several snake venoms contain novel proteins with neurotoxin-like activity.

Agkistrodon↗