Calcium and cAMP: Second Messengers in Gastropod Neurons
Basic research in cell biology over the past 20 years has demonstrated that intracellular free calcium ions (Cai 2+) and cyclic nucleotides (cyclic AMP and cyclic GMP) are critical elements in the internal signaling system of virtually all types of animal and plant cells. There are four common features that distinguish these “second messengers” from other molecules and ions found inside cells: (1) each exists in very low concentrations under basal conditions; (2) the level increases in response to an extracellular stimulus, i.e., first messenger; (3) rapid regulation occurs following elevation; and (4) its presence is a rate-limiting factor in the cell’s response to the stimulus. Thus the internal concentration of a second messenger is the result of a dynamic balance between processes that are continuously elevating the level matched against those which are reducing it.
KeywordsCyclic Nucleotide Absorbance Change Nerve Cell Body Apparent Dissociation Constant Molluscan Neuron
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