Potassium is the major cation (positive ion) inside animal cells, while sodium is the major cation outside animal cells.
pətˈæsiəm ɪz ðə mˈeɪdʒɚ kˈæɾaɪən pˈɑːzᵻtˌɪv ˈaɪɑːn ɪnsˈaɪd ˈænɪməl sˈɛlz, wˌaɪl sˈoʊdiəm ɪz ðə mˈeɪdʒɚ kˈæɾaɪən aʊtsˈaɪd ˈænɪməl sˈɛlz.