Round window membrane permeability. An in vitro model.

The round window membrane of the mongolian gerbil was dissected out, together with its bony niche. The preparation was mounted between two glass chambers representing the middle ear cavity and the perilymphatic space respectively. Passage through the round window membrane did not occur within 3 h when testing high-density lipoprotein with a molecular weight 115-350 kD. Horse-radish peroxidase, with a molecular weight of 48 kD, passed the round window membrane at a mean rate of 6 micrograms/h when the concentration of the protein was 10 g/l in the middle ear chamber. The present in vitro model is considered to be free from leakage artifacts between the chambers. Passage rates for different substances through the round window membrane can be calculated under controlled conditions using this type of in vitro model.