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122 Role of calmodulin on the calcium-dependent regulation of the inositol 1,4,5-trisphosphate receptor
S24 121
MAGNETIC
FIELD
OF ACTIVE
EFFECTS
POTENTIAL.
ON NEUROTRANSMISSION
TOSHIAKI
- FREQUENCY ANALYSES
OSUCA’~.HOZUMI
TATSUOKA”.
I)Dept.of
Phys.
Fac.of
Sci.
.Chiba
Univ.
Z)Dept.of
Anat.
Sch. of
Med.
, Chiba
Univ.,
Inage,Chiba,
effects
on nerve
To investigate frequency bullfrog
analyses under
were affected although
magnetic for
1.5T
field
neurotransmission
steady magnetic field.
by the magnetic field
no effects
of
the
263, Japan
fibers,
we made
sciatic
nerve
Some frequency
in the degenerated
was found in the freshly
of
components
nerve fibers
removed fibers.
122
ROLE OF CALMODULIN ON THE CALCIUM-DEPENDENT REGULATION OF THE INOSITOL 1.4,5-TRISPHOSPHATE RECEPTOR. TAKAYUKI MICHIKAWAI, WI, SEIKO KAWAN02, MASAYASU HIRAOKA2, TEIICHI FURUICHIi, -lr3, iDeot. of Mol. Neurobiol., Inst. of Med. Sci.. Univ. of Tokvo. Tokvo 108: 2De?ot. of Cardiovas. &Med. Res. Ins . Tokvo 113: and 'Mol. : Neurobiol. Lab. Inst. of Ph s. Tsukuba Life Sci. c ent. The inositol 1,4,5-trisphosphate (1~3) receptor (IP3R), an intracellular Ca2+ release channel, plays a key role in intracellular Ca2+ signaling. The IP3R is regulated by cytoplasmic Ca2+ in a biphasic manner with the maximum activity of the channels at Ca2+ concentration of 200 - 300 nM. Thus, it has been suggested there is a feed-back regulation of the IP~R by released Ca2+ itself. Calmodulin (CaM) is a ubiquitous Ca2+ binding protein which binds to a wide variety of proteins in a Ca2+-dependent manner and regulates their functions. We have shown that CaM binds to the type 1 and type 2 IP3Rs in a Ca2+-dependent manner, but its physiological role has not been clarified. To investigate the role of CaM on the "bell-shaped" Ca2+ dependence of the IP3R, we examined the effects of various CaM antagonists on the cerebellar IP3R at the single channel level after channel incorporation into planar lipid bilayers.
123
MECHANISMS SYMPATHLTIC
UNDERLYING NEURONS.
s Dept. of Pharmacol.. Kurume Nabeshima 849. Japan.
LONG-LASTING POTENTIATION TAKAYUKI TOKIMASA. MASAMI
Univ. Sch. of Med.,
Kurume
830.
Japan.
OF M-CURRENT IN BULLFROG YOSHIDA. TAKUYA MITSUMOTO, Dept.
of Physiol.
Saga Med. Sch,
Ratiometiric measurement of the furafluorescence (F340/F380) was combined with standard whole-cell voltage-clamp recordings of M-current in cultured bullfrog sympathetic neurons. The ratio was converted to an absolute value for the concentration of calcium ions ([Cali) using in vivo calibration. M-current showed the long-lasting (I-2 min) potentiation following the inward calcium current (zero mV, 2 s) and subsequent increase in [Cali. The relationship between the M-conductance (at -35 mV) and [Cali was 5 nS vs 140 nM before the calcium current and 16 nS vs 940 nM approximately 10 s after the termination of the calcium current. The M-current potentiation was due primarily to a hyperpolarizing shift of the steady-state activation curve of M-current,
MAGNETIC
FIELD
OF ACTIVE
EFFECTS
POTENTIAL.
ON NEUROTRANSMISSION
TOSHIAKI
- FREQUENCY ANALYSES
OSUCA’~.HOZUMI
TATSUOKA”.
I)Dept.of
Phys.
Fac.of
Sci.
.Chiba
Univ.
Z)Dept.of
Anat.
Sch. of
Med.
, Chiba
Univ.,
Inage,Chiba,
effects
on nerve
To investigate frequency bullfrog
analyses under
were affected although
magnetic for
1.5T
field
neurotransmission
steady magnetic field.
by the magnetic field
no effects
of
the
263, Japan
fibers,
we made
sciatic
nerve
Some frequency
in the degenerated
was found in the freshly
of
components
nerve fibers
removed fibers.
122
ROLE OF CALMODULIN ON THE CALCIUM-DEPENDENT REGULATION OF THE INOSITOL 1.4,5-TRISPHOSPHATE RECEPTOR. TAKAYUKI MICHIKAWAI, WI, SEIKO KAWAN02, MASAYASU HIRAOKA2, TEIICHI FURUICHIi, -lr3, iDeot. of Mol. Neurobiol., Inst. of Med. Sci.. Univ. of Tokvo. Tokvo 108: 2De?ot. of Cardiovas. &Med. Res. Ins . Tokvo 113: and 'Mol. : Neurobiol. Lab. Inst. of Ph s. Tsukuba Life Sci. c ent. The inositol 1,4,5-trisphosphate (1~3) receptor (IP3R), an intracellular Ca2+ release channel, plays a key role in intracellular Ca2+ signaling. The IP3R is regulated by cytoplasmic Ca2+ in a biphasic manner with the maximum activity of the channels at Ca2+ concentration of 200 - 300 nM. Thus, it has been suggested there is a feed-back regulation of the IP~R by released Ca2+ itself. Calmodulin (CaM) is a ubiquitous Ca2+ binding protein which binds to a wide variety of proteins in a Ca2+-dependent manner and regulates their functions. We have shown that CaM binds to the type 1 and type 2 IP3Rs in a Ca2+-dependent manner, but its physiological role has not been clarified. To investigate the role of CaM on the "bell-shaped" Ca2+ dependence of the IP3R, we examined the effects of various CaM antagonists on the cerebellar IP3R at the single channel level after channel incorporation into planar lipid bilayers.
123
MECHANISMS SYMPATHLTIC
UNDERLYING NEURONS.
s Dept. of Pharmacol.. Kurume Nabeshima 849. Japan.
LONG-LASTING POTENTIATION TAKAYUKI TOKIMASA. MASAMI
Univ. Sch. of Med.,
Kurume
830.
Japan.
OF M-CURRENT IN BULLFROG YOSHIDA. TAKUYA MITSUMOTO, Dept.
of Physiol.
Saga Med. Sch,
Ratiometiric measurement of the furafluorescence (F340/F380) was combined with standard whole-cell voltage-clamp recordings of M-current in cultured bullfrog sympathetic neurons. The ratio was converted to an absolute value for the concentration of calcium ions ([Cali) using in vivo calibration. M-current showed the long-lasting (I-2 min) potentiation following the inward calcium current (zero mV, 2 s) and subsequent increase in [Cali. The relationship between the M-conductance (at -35 mV) and [Cali was 5 nS vs 140 nM before the calcium current and 16 nS vs 940 nM approximately 10 s after the termination of the calcium current. The M-current potentiation was due primarily to a hyperpolarizing shift of the steady-state activation curve of M-current,