AJP - Cell Physiology, Vol 255, Issue 6 C724-C730, Copyright © 1988 by American Physiological Society
Role of alpha 1- and alpha 2-adrenergic receptors in Cl- transport across frog corneal epithelium
T. C. Chu and O. A. Candia
Department of Ophthalmology, Mount Sinai School of Medicine of the City University of New York, New York 10029.
Norepinephrine, 10(-6) M, reduced Cl- transport by 26% in 75% of isolated
frog corneal epithelia. This inhibition was not previously reported. Since
beta-adrenergic agonists are known to only stimulate Cl- transport, the
action of specific alpha 1- and alpha 2-agonists on Cl- transport and
electrical parameters was investigated. Phenylephrine, an alpha 1-agonist
always stimulated the Cl(-)-dependent short-circuit current (Isc), but less
than the beta-agonists. UK-14,304-18 (UK), a selective alpha 2-agonist,
reduced both the Isc (by 31% at 10(-5) M) and the stroma-to-tear
unidirectional Cl- flux. UK hyperpolarized the apical membrane potential
difference and increased the transepithelial resistance and
apical-to-basolateral resistance ratio. UK reduced forskolin-stimulated
adenylate cyclase activity by 36%. The electrophysiological effects of UK
are consistent with a reduction of the Cl- permeability at the apical
membrane. Pretreatment with UK sensitized the tissue for a greater effect
by forskolin. Results show that the frog corneal epithelium also possesses
alpha 1- and alpha 2-receptors, the latter negatively coupled to the
adenylate cyclase system. Cl- transport is thus regulated by an interaction
between the positive effects of beta- and alpha 1-stimulation and the
negative influence of alpha 2-stimulation.
