bioactive molecules ONLY active via microinjection?

[mark]

Kate Michie wrote:
> 
>  I am doing some experiments testing various drug delivery methods and I
> want to know if anyone knows of any smallish molecules that are bioactive
> BUT cannot diffuse across plasma membranes.(eg. molecules that must be
> mircoinjected) to be used as a cargo? Thanks for any suggestions .

WhT DO YOU mean injectable cargo?  THere are some CA++ binding molecules 
that get into a cell and are converted to a molecule that can't get mack 
out?