INFLUENCE OF AMPHOTERICIN-B ON THE SODIUM-PUMP OF PORCINE LENS EPITHELIUM

Active transport by Na+-K+-ATPase in the monolayer of lens epithelium is vital for the regulation of sodium and potassium levels within the mass of fiber cells that make up the bulk of the lens. In this study, experiments were conducted using porcine lenses to test whether Na+-K-ATPase activity in the epithelium is altered when the permeability of lens cell plasma membranes is increased by the ionophore amphotericin B. After 24 h, sodium was significantly (P < 0.01) elevated in lenses exposed to 5 or 10 mu M amphotericin B. Amphotericin B stimulated Rb- 86 uptake, probably through an increase of cytoplasmic sodium concentr ation due to increased inward sodium leak; the rate of ouabain-sensiti ve potassium (Rb-86) uptake by intact lenses was significantly increas ed by amphotericin B at 5 mu M (P < 0.05) and 10 mu M (P < 0.01). Afte r 24 h, the epithelium from lenses exposed to amphotericin B had an Na +-K+-ATPase activity that was more than twofold higher (P < 0.01) than the Na+-K+-ATPase activity in control lenses. By immunoblot, there wa s an increase in Na+-K+-ATPase catalytic (alpha) subunit immunoreactiv e polypeptide in the epithelium of lenses exposed to amphotericin B. T he increase stemmed from a marked increase of Na+-K+-ATPase alpha(2)-i mmunoreactive polypeptide but little change in the amount of alpha(1)- immunoreactive protein. As judged by immunoblot experiments, the amoun t of Na+-K+-ATPase beta(1)-immunoreactive polypeptide also appeared to be higher in the epithelium of amphotericin B-treated lenses compared with control lenses. In summary, these results suggest that in respon se to a permeability challenge with amphotericin B, the porcine lens e pithelium is able to increase the activity of Na+-K+-ATPase. The same permeability challenge also appears to stimulate the biosynthesis of N a+-K+-ATPase catalytic subunit as well as glycoprotein subunit polypep tides.