Calcium and Cyclic AMP in Cell Activation

Cyclic nucleotide has been found to play an important role in the activation of many different cells by specific stimuli. It has been found to be involved in the phenomena of enzyme induction in bacteria of aggregation in the cellular slime mold Dictyostelium discoideum of the action of many hormones, and in a wide variety of secretory processes including the release of synaptic transmitters. One need only contrast the function of these enzymes in liver mitochondria to those in insect flight muscle to make the point. In the liver, they participate, in times of fasting, in the conversion of amino acids to cytoplasmic carbohydrate precursors, of fatty acids to ketone bodies, and to cytoplasmic reducing equivalents. In the case of secretion and peptide hormone action, the requirement for calcium and the activation of membrane-bound adenyl cyclase both appear in many of the same systems. An important aspect of this relationship involves the effects of cyclic AMP and first messenger on calcium uptake and release by particular cells.