Effect of lymph composition on an in vitro preparation of the alligator lizard cochlea.

The effects of different artificial lymphs on the cochlear duct of the alligator lizard were studied in an in vitro preparation. The duct was dissected and cemented to the glass floor of a chamber that had been filled with an artificial lymph. The vestibular membrane was removed and latex beads (1-5 microns in diameter) were allowed to settle on the endolymphatic surface of the duct. During perfusion with an artificial lymph solution, the positions of beads were measured and video images of the duct were obtained. Artificial lymphs were isosmotic and included artificial endolymph (AE), artificial perilymph (AP), Leibovitz's L-15 culture medium, an AE solution whose calcium concentration was the same as that of AP, and AE and AP solutions in which gluconate was substituted for chloride ions. Results obtained in AE were consistently different from those in other lymphs. The displacements of beads, the projected area of the papilla, the occurrence of blebs, and direct observation of cells in the duct all indicated that the tissue swelled in AE (with or without 2 mmol/l Ca) but showed no consistent shrinking or swelling in any of the other artificial lymphs. Thus for the solutions we used, the presence of both potassium and chloride was required to elicit the swelling response to isosmotic artificial lymphs. There were some regional differences in the swelling response: the swelling of the endolymphatic surface of the tissue in a direction orthogonal to the basilar membrane surface was smaller on the free-standing region of the basilar papilla than either on the tectorial membrane or on the hyaline epithelial cells. The preparation was osmotically stable in AP and in both AE and AP solutions in which gluconate was substituted for chloride ions. After exposure to these solutions for as much as 300 min, the preparation showed no gross signs of deterioration visible with the light microscope, and continued to exhibit a highly specific osmotic response to the composition of the bathing medium.