The gas manifold is not normally used with the horizontal chamber. Normally, if a gassed solution needs to be introduced into the horizontal chamber it will first be bubbled into the media, which is then pumped into the basolateral chamber.

Since the gas manifold is basically twelve needle valves mounted into an aluminum housing with input/output tubes, it can be used with the horizontal chambers, but its never been sold this way.

Here's a brief description taken from the Navicyte User's Manual.

The Horizontal Diffusion Chamber System is designed for transport and toxicology studies using cells and tissues which are exposed to an air interface in their normal in vivo environment such as nasal, pulmonary, corneal or dermal cells.

The chambers create an environment in which the apical surface of the tissue or cell monolayer is exposed to liquids, semi-solid compounds or gases, while the basolateral surface is perfused with medium.

Either a peristaltic or a syringe pump (not included with the system) can be used to perfuse the lower surface of the Snapwell™ insert, usually the basolateral surface. The apical (upper) surface of the diffusion chamber can be used in either open or closed configuration, the cell surfaces being more accessible for drug transport or cytotoxicity testing of liquids and semi-solid materials in the open configuration.

In the closed configuration, cells can be exposed to solutions, perfused with gas, or gas pressure can be applied.