ION-TRANSPORT BY PRIMARY CULTURES OF MONGOLIAN GERBIL MIDDLE-EAR EPITHELIUM

The transport properties of Mongolian gerbil middle ear epithelial cells grown in primary culture were studied. These cells formed polarized monolayers that exhibited domes on nonporous supports. On porous supports, monolayers developed an apical-negative transepithelial electric potential difference (V(T) = - 37.2 +/- 2.7 mV) and a transepithelial resistance (R(T) = 519 +/- 56-OMEGA.cm2). The short-circuit current equivalent (I(eq)) was 62.4 +/- 6.2-mu-A/cm2 (mean +/- SE, n = 15). Na+ and Cl- accumulated in the basal bath and generated a basolateral hyperosmolarity that drove a net water flow. Amiloride (10-mu-M), when added to the apical but not to the basal bath, induced a 23.4 +/- 1.5 mV and 44.1 +/- 1.3-mu-A/cm2 decrease of V(T) and I(eq), respectively, while R(T) increased by 403 +/- 69-OMEGA.cm2 (P < 0.001, n = 15). Exposure of the monolayers to a low-Cl- solution (30 mM) enhanced the transepithelial potential, possibly by means of a Cl- secretion through apical Cl- channels. Isoproterenol (10(-4) M basolateral) increased intracellular adenosine 3',5'-cyclic monophosphate (cAMP) content (concentration of half-maximal response = 2.5 x 10(-7) M) and decreased V(T), R(T), and I(eq). The isoproterenol-induced fall of V(T) occurred even in the presence of low-Cl- solutions. This suggested an increase of the paracellular pathway conductance, although there was no significant modification of the mannitol permeability. In conclusion: 1) middle ear epithelial monolayers in primary culture show an absorptive function related to apical Na+ absorption through amiloride-sensitive channels; 2) isoproterenol, via an increase in cAMP content, may increase the conductance of the paracellular pathway; and 3) such a beta-adrenergic modulation of transport may provide a pathophysiological basis for the mucociliary clearance impairment that initiates chronic otitis media.