Shinji Yamaguchi

Serine Residue in the IIIS5-S6 Linker of the L-type Ca2+ Channel α1C Subunit Is the Critical Determinant of the Action of Dihydropyridine Ca2+Channel Agonists

The dihydropyridine (DHP)-binding site has been identified within L-type Ca2+ channel α1Csubunit. However, the molecular mechanism underlying modulation of Ca2+ channel gating by DHPs has not been clarified. To search for novel determinants of high affinity DHP binding, we introduced point mutations in the rat brain Ca2+ channel α1C subunit (rbCII or Cav1.2c) based on the comparison of amino acid sequences between rbCII and the ascidian L-type Ca2+ channel α1 subunit, which is insensitive to DHPs. The α1C mutants (S1115A, S1146A, and A1420S) and rbCII were transiently expressed in BHK6 cells with β1a and α2/δ subunits. The mutation did not affect the electrophysiological properties of the Ca2+channel, or the voltage- and concentration-dependent block of Ca2+ channel currents produced by diltiazem and verapamil. However, the S1115A channel was significantly less sensitive to DHP antagonists. Interestingly, in the S1115A channel, DHP agonists failed to enhance whole-cell Ca2+ channel currents and the prolongation of mean open time, as well as the increment of NP o. Responsiveness to the non-DHP agonist FPL-64176 was also markedly reduced in the S1115A channel. When S1115 was replaced by other amino acids (S1115D, S1115T, or S1115V), only S1115T was slightly sensitive to S-(−)-Bay K 8644. These results indicate that the hydroxyl group of Ser1115 in IIIS5-S6 linker of the L-type Ca2+ channel α1C subunit plays a critical role in DHP binding and in the action of DHP Ca2+ channel agonists.

DHP-insensitive L-type-like Ca channel of ascidian acquires sensitivity to DHP with single amino acid change in domain III P-region

TuCa1, an ascidian homolog of L‐type Ca channel α1‐subunit, has many critical sites required for binding 1,4‐dihydropyridines (DHPs), but is insensitive to DHPs and methyl 2,5‐dimethyl‐4‐[2‐(phenylmethyl)benzoyl]‐1H‐pyrrole‐3‐carboxylate (FPL‐64176). We have substituted Ser for Ala1016 at the P‐region of domain III in TuCa1 (TuCa1/A1016S) and functionally expressed the channel in Xenopus oocyte along with rabbit α2/δ and β2b. TuCa1/A1016S has gained DHP sensitivity as high as that of a mammalian neuronal L‐type Ca channel (rbCII), but remained resistant to FPL‐64176. These results reinforce the view that Ser1016 in TuCa1/A1016S participates in DHP binding, but there exist other novel sites that fully acquire sensitivity to FPL‐64176.

Suppression of the ecdysteroid-triggered growth arrest by a novel Drosophila membrane steroid binding protein

Ecdysteroid is a crucial steroid hormone in insects, especially during metamorphosis. Here, we show that the Drosophila membrane steroid binding protein (Dm_MSBP) is a novel structural homolog of the vertebrate membrane‐bound receptor component for progesterone. Dm_MSBP exhibited binding affinity to ecdysone when expressed on the cell surface of Drosophila S2 cells. In S2 cells, the stable overexpression of Dm_MSBP suppressed the growth arrest triggered by 20‐hydroxyecdysone and prevented the temporal activation of extracellular signal‐regulated kinase proteins. These results suggest that Dm_MSBP is a membranous suppressor to ecdysteroid and blocks the signaling by binding it in extracellular fluid.

Simulation of high GWR behavior in the water-dissolved natural gas reservoir.

A numerical model was developed to study the production behavoir in the Mobara type water-dissolved natural gas reservoir which was composed of horizontal beds of alternating mudstones and sandstones. The model consists of the mathematical description of a horizontal, two phase (water and methane gas) flow in the two-dimensional sandstone layer, assuming the vertical, one dimensional diffusion of the desorbed gas from the mudstone.The methane adsorbtion volume for the mudstone was calculated assuming the Langmuirs adsorbtion isotherm. The model was applied to simulate the behavior of the reservoir of the Mobara type gas field.From the results of simulation, it was concluded that the model was valid for the Mobara type gas reservoir and that the effects of desorbed gas from the mudstone on the GWR behavior could be simulated by the proposed model.

Natural gas treatment and pipeline transportation at well site

This paper presents the numerical models for the estimation of temperature drop in a low temperature separator and pressure drop in a horizontal pipeline. As a basis for both models, the nume-rical models for flash calculations are fully taken into consideration. These models were applied to some field cases. The calculation results were compared with measured results, and reasonable agreement was observed. These models can be utilized for the selection of separator conditions to prevent the generation of hydrate and for the decision of an inside diameter of a horizontal pipeline in designing surface production facilities of natural gas.

Simulation of Transient Pressure Behavior in a Fractured Geothermal Reservoir

This paper presents a numerical model and an electrical model of a fractured reservoir. Pressure drawdown and buildup tests are simulated with these models. The results of the numerical model agree with those of the electrical model. Further study indicates that the effective transmissibility for a fractured reservoir and the storage capacity ratio can be estimated by the transient pressure techniques.