Trie Implementation: using Int vs Char

I'm currently trying to implement a trie in C in order in order to make a speller check (dictionary is taken from a text file loaded into the trie structure).

Here is my current struct for nodes (taken from http://ift.tt/1sBl8Q8):

typedef struct trieNodeTag 
{
    char key;
    struct trieNodeTag *next, *children;
} trieNodeT;

key being the letter of each word to load in memory.

My question is the following: does that make a difference in memory / speed to use a type int for key ? Is a char treated directly as an int ?

Thank you !