How to provide divalent cation in medium?

[EddieWK]

Dear,

I have a question about medium used in tissue cultruing.  I'm currently
doing functional assays using RPMI 1640 medium, in which ligand binding on
cells may occur.  I would like to know if I want some "divalent cation"
present in the medium to test the nature of binding, anyone can tell me what
chemical compound(s) I should add into the medium to provide the "divalent
cation", like Ca++?  or other kind of medium can be used instead of RPMI.
Thank you in advance.

Regards

Eddie