ABSTRACT Among second messengers, Ca2+, cAMP, cGMP and IP3, Ca2+ is the most potent messenger, because only Ca2+ has a large nember of merits and small number of demerit as a second messenger. First merit is its small difussion constant which clarified the difference between Ca2+ that entered into the cell from external and that released from internal store. They will cause different signaling pathways between the two. The former will activate CaMK and the latter activate PKC dominantly. Second merit of Ca2+ as a second messenger is that the level of intracellular Ca2+ chanrged largely (10-7M →10-6M) when receptor is activated, comparing with cyclic nucleotide concentration charges for the receptor stimulation. This may be one of the reasons why Ca2+ imaging was fully successful. Thus Ca2+ imaging was very useful for the research of Ca2+ signaling pathway, so far. PKC imaging is also useful for the studying of Ca signaling mechanism, because activation of PKC is intermediate achieve stage of Ca2+ cascade. From this point, phosphorylation of functional protein will start and the final goal will be the change in the K+ channel conductance which will induce long lasting potentiation in the electric characteristics of the neuron. However residual signaling pathway is also important to elucidate the whole of signal transduction pathway. Unfortunately other second messenger, however, is not suitable to make imaging. In order to overcome their difficulties we developed thermal imaging system to visualize how information is transferred from receptor to channel. Investigation of heat production associated with the nerve and muscle excitation was initiated by A.V. Hill and developed by I. Tasaki. Their work is a kind of epoch making one but the system they used had no ability to get spacial information. The thermal imaging system could solve this problem, and can open new field of imaging analysis. Furthermore imaging analysis is very powerful method to appeal to the scientists belonging to the outside of this field. In spite of these numerous merits, the imaging analysis has small number of demerit. That is uncertainty in the quantitative analysis of imaging date. We have no decisive method at present but if it will be used adequately, complex interaction between cAMP cascade and Ca2+ one, PLC-Ca2+ pathway and NMDA-Ca2+ one, will be uncovered in these few years.
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