Second messengers: Rate of formation as an index of receptor reactivity

Abstract

Generation of a second messenger upon stimulation of a metabotropic membrane receptor is the first biochemical reaction in the process of translation of a signal approaching the cell into the cellular response. Thus, the measurement of the rate of generation of these intracellular chemical signals may be a convenient way to assess the functional state of the receptor. The basic methodologies for assessment of the formation of cyclic AMP and inositol phosphates are described. Examples from our laboratory show how the measurement of these messengers may be employed in studies on receptor adaptation to permanently changed neurotransmitter availability, the discrepancy between the changes of receptor densities and functional up- or down-regulation, cooperativity of receptors, mechanisms of the action of drugs, neurotransmission changes in senescence and comparative neurochemistry.