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:…to regulate the release of ions and metabolites, such as ATP, from mitochondria (Colombini et al., 1996; Rostovtseva and Colombini, 1996), and recent evidence suggests that BCL-xL may also control the flux of ATP and phosphocreatine across the outer membrane (Vander Heiden et al., 2000, 2001).
Category: