That seems like a useless/bad/weird thing to do, but whatever, here is how to save row #37 to cell array "ca" in cell number 5:
ca{5} = uint8(grayImage(37, :));
I extracted row #37 of an image called "grayImage", all columns of that row, then cast it to uint8, and then assigned it as the contents (because I used curly braces) of cell #5 of a cell array called "ca".
Please read the FAQ to get a more intuitive feel for cell arrays and when to use parentheses or braces.
