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:Hence, this result is consistent with the previous findings that both mammalian atrial and ventricular myocytes isolated from several different species, including humans, contain muscarinic receptors (15, 17, 18, 19, 38).
Category: