Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:For example, the novel PKCε and PKCδ isoforms were shown to mediate the inhibitory effect of phorbol ester PMA and serotonin on Cl−/OH− exchange, respectively [24, 38], in Caco2 cells.
Category: