Could you link the paper? It is hard to know what you are referring to based on this question alone. I'm guessing you are talking about fast or slow afterhyperpolarizations, which are usually mediated by different types of calcium dependent potassium channels with faster or slower kinetics. I suppose you could also be talking about the activation of GABA-A versus GABA-B receptors. GABA-A receptors are ion channels that mediate fast chloride entry into the cell when GABA binds versus GABA-B receptors that are g-protein coupled receptors and act much more slowly.