Understanding osmolality - (Oct/10/2011 )

Hello:

I am currently trying to induce cell contraction by treating my cells with 60 mM potassium chloride (KCl) in pre-made medium. Since I don't have a way of reducing NaCl content in the medium to compensate for the increase in osmolality, I need to do a control experiment in which I treat the cells with sucrose, so that I can show contraction is due to direct effect of KCl and not the increase in osmolality. However I don't really understand how calculations of osmolality works . . . Is adding 60 mM KCl equivalent to adding 60 mOsm? How much sucrose do I need to increase osmolality by the same amount? I would really appreciate the help, thank you!

KCl in solution produces 2 ionic forms, K⁺ and Cl^-, which are independent osmoles, thus a 1M KCl solution is a 2 Osm solution...