Effect of loop diuretics on bullfrog cornea epithelium

Electrical signaling in control of ocular cell behaviors

Epithelia of the cornea, lens and retina contain a vast array of ion channels and pumps. Together they produce a polarized flow of ions in and out of cells, as well as across the epithelia. These naturally occurring ion fluxes are essential to the hydration and metabolism of the ocular tissues, especially for the avascular cornea and lens. The directional transport of ions generates electric fields and currents in those tissues. Applied electric fields affect migration, division and proliferation of ocular cells which are important in homeostasis and healing of the ocular tissues. Abnormalities in any of those aspects may underlie many ocular diseases, for example chronic corneal ulcers, posterior capsule opacity after cataract surgery, and retinopathies. Electric field-inducing cellular responses, termed electrical signaling here, therefore may be an unexpected yet powerful mechanism in regulating ocular cell behavior. Both endogenous electric fields and applied electric fields could be exploited to regulate ocular cells. We aim to briefly describe the physiology of the naturally occurring electrical activities in the corneal, lens, and retinal epithelia, to provide experimental evidence of the effects of electric fields on ocular cell behaviors, and to suggest possible clinical implications.

Active chloride transport in the pigmented rabbit conjunctiva

The present study demonstrates, for the first time, that the excised pigmented rabbit conjunctiva is a tight barrier capable of active Cl- transport. The transepithelial potential difference was 17.7 +/- 0.8 mV (tear-side negative), the short-circuit current was 14.5 +/- 0.7 microA/cm2, and the transconjunctival resistance was 1.3 +/- 0.1 k omega.cm2 for n = 45 tissues. Various inhibitors including ouabain (a Na+/K(+)-ATPase inhibitor), amiloride (a Na+ transport blocker), N-phenylanthranilic acid (a chloride transport inhibitor), bumetanide (an inhibitor of Na(+)-(K+)-Cl- cotransport process), and BaCl2 (a K+ channel blocker) were used on the mucosal and serosal sides of the tissue mounted in Ussing chambers to determine the involvement of the respective ion transport processes in the observed short-circuit current across the conjunctiva. The results suggest that a Cl- conductive pathway is present on the mucosal side of the conjunctiva, whereas Na+/K(+)-ATPase, Na(+)-(K+)-Cl- cotransport process, and K+ conductive pathways are present on its serosal side. Amiloride-sensitive Na(+)-conductive pathways do not appear to be present on either side of the pigmented rabbit conjunctiva.