1989 Fiscal Year Final Research Report Summary
Cyclic Nucleotide-Sensitive Ion Channels In Olfactory Receptor Cell Membrane.
| Project/Area Number |
63540557
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
動物発生・生理学
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| Research Institution | Hokkaido University |
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Principal Investigator |
SUZUKI Noriyo Hokkaido University, Faculty of Science, Lecturer, 理学部, 講師 (10001851)
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| Co-Investigator(Kenkyū-buntansha) |
SHINOZAWA Takao Gunma University, Faculty of Technology, Associate Professor, 工学部, 助教授 (30025449)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Olfactory Transduction Mechanism / Cyclic Nucleotide-Sensitive Ion channels / Dynamics of Ion Channel Activity / Cation Selectivity / Unit Conductance / Cation Channels / Purification of Olfactory Cilia / Ion Channel Protein |
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| Research Abstract |
It has been proposed that an adenylate or guanylate cyclase cascade is involved in coupling odorant-activation of olfactory receptor molecule with conductance changes, giving rise to olfactory receptor potentials. Cyclic nucleotides have been thought to act on the conductance as intracellular messengers. Although the odorant-activation of adenylate cyclase has been examined extensively, molecular nature of the proteins in the cascade and the mechanism how these as a whole regulate the conductance have not been fully understood. We have focused on the studies on electrical properties and molecular nature of the cyclic nucleotide-activated ion channels, and have found that the channels have the following characteristics: (1)The channels are activated directly by both cyclic AMP and cyclic GMP. This indicates that the phosphorlylation of channel molecule is not required in its activation. There is a possibility whether olfactory adenylate cyclase is not a single species of enzyme or does
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not have a substrate specificity for production of different cyclic nucleotides. (2)The channels have a low cationic selectivity. Many monovalent and divalent cations can pass through the channels. Thus, the channels may be categorized into a species of the "cation channels". (3)The channel molecule has at least two cooperative binding sites for the cyclic nucleotides and their affinity (K_<1/2>) to the cyclic nucleotides ranges between 3 and 5 uM. (4)The channels have a unit conductance of 24 pS. The distribution of channel open times is expressed as a sum of two exponentials. The time constants are 10.1 msec and 0.9 msec at 1 uM cAMP. The channels are blocked by divalent cations likely in a voltage-dependent manner. This raises the possibility that divalent cations play roles in the adaptation process through whether their direct blockage of the channels or their activation or inhibition of phosphodiesterase dr adenylate cyclase activity. (5)The channels are distributed in not only olfactory cilia but also dendrite and soma membrane. (6)The candidate channel molecule is a protein with a molecular mass of 35-39 kDa. Less
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