Site and mode of adrenaline action on chloride transport across the rabbit corneal epithelium.

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Abstract
Membrane events accompanying adrenaline[epinephrine]-stimulated Cl- secretion by the isolated rabbit corneal epithelium were investigated with microelectrodes. Pulses of adrenaline (5 .times. 10-10 M final concentration) delivered to either side of the epithelium produced a transient decrease in epithelial resistance occurring at the outer membrane of the squamous cell. This response was reversible and could be blocked completely by total Cl- substitution with .**GRAPHIC**. Adrenaline generally produced a small transient increase in epithelial potential occurring also at the squamous cell outer membrane. Reversal potentials obtained for the adrenaline response were 45.1 mV for corneal potential and 22.8 mV for outer membrane. Adrenaline always hyperpolarized the epithelial potential when the tear side was bathed in Cl-free solution. Reversing the gradient (Cl--free on the stromal side) slowly and consistently changed the response to a depolarization which reached a steady level after 2 h. The reversal potential of the outer membrane for the adrenaline response was a semilogarithmic function of the tear side Cl- concentration over a broad range with a slope of 56 mV/decade. The reversal potential was zero at a tear side Cl- concentration of 41.5 mM, which value may be taken to be representative of cell Cl- concentration. After abolishing the adrenaline response by perfusing both sides of the tissue with Cl--free solution, reintroduction of Cl- to the stromal side led to a recovery of the epithelial potential response in the hyperpolarizing direction. The recovery of the response was inhibited by ouabain (10-5 M). The following model was proposed for the influence of adrenaline on anion transport in the epithelium: Cl- is transported against an electrochemical potential gradient into the cells from the stromal side by an active process linked to Na+-K+ activated ATPase. Normally a slight gradient exists from cells to tears favoring the passive outward diffusion of Cl-. This latter process is enhanced by adrenaline, which increases cell cyclic AMP, in turn increasing the passive Cl- permeability of the outer cellular membrane.