Bioelectric properties of gerbil middle ear epithelia

Biochemical analysis of middle ear effusions provides indirect evidence of epithelial function, but no direct studies of middle ear epithelial function have been published. This study uses cell culture techniques to study the bioelectric properties of these cells and their response to pharmacologic agents. Middle ear epithelial cells were isolated by protease and DNase digestion and cultured on collagen matrices. A transepithelial potential difference (PD) measured by calomel half cells peaked by day 8 in culture (PD = -8.6 +/- 1.6 mV). Resistance and short-circuit current (ISC) were calculated to be 307 +/- 46 omega/cm2 and 28 +/- 4.1 A/cm2, respectively. At peak PD, cultures were mounted in flux chambers (Ussing), and pharmacologic agents were applied. Amiloride (10(-4) mol/L), an inhibitor of Na transport, decreased ISC by 52.3% +/- 4.9% but had no effect when added basolaterally. Carbachol (10(-4) mol/L), a cholinergic agonist, had no effect when added to the apical bath but increased ISC by 62.9% +/- 12.4% when added basolaterally. Isoproterenol (10(-4) mol/L), a beta-adrenergic agonist, increased ISC by 4.8% +/- 1.8% when added apically but had no effect when added basally. These results indicate that the epithelium lining the middle ear plays a role in regulating the quantity and composition of liquid in the middle ear by ion transport and that cell culture may be useful in studying this phenomenon.