Updating function values

1

I have 3 variables on the _root timeline.

var a = 50;
var b = 75;
var c = 100;

then i have a prototype which uses those

MovieClip.prototype.myName = function(a,b,c){
…
}

I then have 3 sliders which change the values or a,b and c.

My question is: How do I get the prototype to update the values of a,b and c as the sliders change the values of the variables?

-Regards,
Halian