Consider Neuron B in the frog central nervous system whose plasma membrane has a previously unknown channel that is selectively conductive to a newly discovered divalent cation named DIVCAT with a valence of +2. 

The threshold for an action potential in Neuron B is -55 millivolts and the resting potential for Neuron B is -70 mill volts.  The DIVCAT channel in Neuron B is part of an ion tropic receptor with an extracellular binding site for the newly discovered ligand LGD.  When LGD binds to its binding site, there is an increase in the DIVCAT conductance of Neuron B.  Neuron A synapses onto Neuron B.  Neuron A's neurotransmitter is LGD.

A. The intracellular concentration of DIVCAT is 1000 times greater than the extracellular concentration of DIVCAT. In response to an action potential in Neuron A, there will be: a decrease in the membrane voltage of Neuron B; a decrease in the amount of intracellular DIVCAT in Neuron B; and an inhibitory postsynaptic potential in Neuron B.

B. The intracellular concentration of DIVCAT is 100 times greater than the extracellular concentration of DIVCAT. In response to an action potential in Neuron A, there will be: an increase in the membrane voltage of Neuron B; an increase in the amount of intracellular DIVCAT in Neuron B; and an inhibitory postsynaptic potential in Neuron B.