jQuery and Prototype events

Question

I have a Prototype code that is triggered upon 'load' event:

  Event.observe($(imageEl), 'load', this.someFunction.bind(this));

When I create 'Real' event using jQuery code like

  jQuery(...imageEl selector...).attr("src", filename);

it fires the Prototype code (someFunction). Good!

Next I try to fire the Prototype code using jQuery trigger:

  jQuery(...imageEl selector...).trigger('load');

But now, nothing happen i.e. this line doesn't fire the Prototype code.

Any idea how to trigger a Prototype event from jQuery?

Thanks, Sty