Masuhide Yakehiro
International University, Cambodia
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FEBS Letters | 2000
Takahiro Kimura; Eiji Kinoshita; Kaoru Yamaoka; Tsunetsugu Yuki; Masuhide Yakehiro; Issei Seyama
Grayanotoxin I (GTX I) is a diterpenoid extracted from the family of Ericaceae that binds to Na+ channels and causes persistent activation. We investigated the interaction of GTX I with the amino acid residues I1575, F1579 and Y1586 in transmembrane segment D4S6 of μ1. In F1579A, GTX shifted the threshold potential about 50 mV in the hyperpolarizing direction and modified Na+ channels twice as efficiently as that in wild‐type. In contrast, these GTX‐effects were eliminated completely in the I1575A mutant and were reduced substantially in mutant Y1586A. Lysine substitution for F1579 significantly reduced and for Y1586 completely eradicated the GTX‐effect. Our data suggest that the GTX receptor site shares overlapping but non‐identical molecular determinants with BTX in D4S6 and has common molecular determinants in D1S6.
The Journal of Physiology | 2001
Tsunetsugu Yuki; Kaoru Yamaoka; Masuhide Yakehiro; Issei Seyama
1 Distinct properties of grayanotoxin (GTX) among other lipid‐soluble toxins were elucidated by quantitative analysis made on the Na+ channel in frog ventricular myocytes. 2 GTX‐modified current (IGTX) was induced strictly in proportion to the open probability of Na+ channels during preconditioning pulses irrespective of its duration, amplitude or partial removal of inactivation by chloramine‐T. This confirms that GTX binds to the Na+ channel exclusively in its open state, while batrachotoxin (BTX) was reported to be capable of modifying slow‐inactivated Na+ channels, and veratridine exhibited voltage‐dependent modification. 3 The GTX‐modified channel did not show any inactivation property, which is different from reported results with veratridine and BTX. 4 Estimated unbinding rates of GTX were in reverse proportion to the activation curve of GTX‐modified Na+ channels. This was not the previously reported case with veratridine. 5 A model including unbinding kinetics of GTX and slow inactivation of unmodified Na+ channels in which GTX was permitted to bind only to the open state of Na+ channels indicated that unbinding reactions of GTX occur only in the closed state.
Biochemical and Biophysical Research Communications | 2002
Hiroshi Maejima; Eiji Kinoshita; Tsunetsugu Yuki; Masuhide Yakehiro; Issei Seyama; Kaoru Yamaoka
We located a novel binding site for grayanotoxin on the cytoplasmic linkers of voltage-dependent cardiac (rH1) or skeletal-muscle (mu 1) Na(+) channel isoforms (segments S4-S5 in domains D1 and D4), using the alanine scanning substitution method. GTX-modification of Na(+) channels, transiently expressed in HEK 293 cells, was evaluated under whole-cell voltage clamp, from the ratio of maximum chord conductance for modified and unmodified Na(+) channels. In mu 1, mutations K237A, L243A, S246A, K248A, K249A, L250A, S251A, or T1463A, caused a moderate, but statistically significant decrease in this ratio. On making corresponding mutations in rH1, only L244A dramatically reduced the ratio. Because in mu 1, the serine at position 251 is the only heterologous residue with respect to rH1 (Ala-252), we made a double mutant L243A&S251A to match the sequence of mu 1 and rH1 in S4-S5 linkers of both domains. This double mutation resulted in a significant decrease in the ratio, to the same extent as L244A substitution in rH1 did, indicating that the site at Leu-244 in rH1 or at Leu-243 in mu 1 is a novel one, exhibiting a synergistic effect of grayanotoxin.
Pflügers Archiv: European Journal of Physiology | 2000
Kaoru Yamaoka; Masuhide Yakehiro; Tsunetsugu Yuki; Hideaki Fujii; Issei Seyama
Japanese Journal of Physiology | 1999
Hidemasa Ishii; Eiji Kinoshita; Takahiro Kimura; Masuhide Yakehiro; Kaoru Yamaoka; Keiji Imoto; Yasuo Mori; Issei Seyama
Molecular Pharmacology | 2001
Takahiro Kimura; Kaoru Yamaoka; Eiji Kinoshita; Hiroshi Maejima; Tsunetsugu Yuki; Masuhide Yakehiro; Issei Seyama
Molecular Pharmacology | 2000
Masuhide Yakehiro; Tsunetsugu Yuki; Kaoru Yamaoka; Toshiaki Furue; Yasuo Mori; Keiji Imoto; Issei Seyama
Hiroshima journal of medical sciences | 1988
Hiroshi Miyoshi; Masuhide Yakehiro; Atsushi Fujiwara; Issei Seyama
Hiroshima journal of medical sciences | 1997
Toshiaki Furue; Masuhide Yakehiro; Issei Seyama
Hiroshima journal of medical sciences | 1992
Masuhide Yakehiro