What type of agent would be most likely to disrupt the structures of microvilli?

The addition of the Calcium Ion (Ca++) is likely to disrupt the structures of microvilli.

Some cells that have a role in absorption or secretion contain microvilli, protrusions of the membrane, due to which the membrane surface area is increased and therefore it leads to more effective diffusion of different molecules through the membrane. They are also involved in cellular adhesion.

Microvilli consist of actin filaments, that are tightly packed and cross-linked, at its core. Microvilli have a big role in the gastrointestinal tract where they have a function in the absorption of nutrients, and therefore they contain enzymes that break down nutrients into compounds that are easy to absorb.

Certain diseases lead to the destruction of microvilli, like in some types of E. Coli infections, and this destruction is caused by the rearrangement of the host cells cytoskeleton which then leads to diarrhea and the disruption the normal process of absorption.

The filaments that are a part of the microvilli structure contain actin and calmodulin which are proteins that make up the filaments of the microvilli. It has been shown that the addition of the Calcium Ion (Ca++) to the cores of the microvilli causes a drastic disruption of these filaments by participating in the solubilization of a large portion of the actin and calmodulin proteins. Ca++ reacts with these proteins, binds to them, and reduces the tightly packed structure of the microvilli filaments.