Neuronal Calcium Signaling

We learned in the previous chapter that neurotransmitter released into the synaptic cleft is the initial, often noisy, messenger of presynaptic information to the postsynaptic cell. Although this message is transcribed into a transient conductance change its effect remains transient unless supported by the postsynaptic cell's network of second messengers. Ca 2+ , the most important of the second messengers, triggers change that activates a host of biochemical pathways (recall Figure 13.1) that have been found necessary for many (but not all) forms of pre- and post-synaptic plasticity. In this chapter we will work from the outside in. In the first section we develop and illustrate the principal types of currents that carry calcium across the plasma membrane. In the subsequent section we discuss the buffering, diffusion, exchange and extraction of cytosolic calcium and its modulatory effect on the cell's firing rate. We then consider the remarkable ability of cytosolic calcium to trigger its own release from the cell's endoplasmic reticulum, see Figures 14.1 and 14.2. We then build and integrate models of ryanodine, IP 3 and metabotropic glutamate receptors and demonstrate that the endoplasmic reticulum functions as a “neuron within a neuron” in the sense that it supports the active propagation of intracellular calcium waves.