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(Hypertension. 1996;28:440-443.)
© 1996 American Heart Association, Inc.
Articles |
Altered Lens Short-Circuit Current in Adult Cataract-Prone Dahl Hypertensive Rats
Research and Medical Services, San Juan VA Medical Center, Department of Pharmacology and College of Health Related Professions, University of Puerto Rico, Medical Sciences Campus, and Departments of Ophthalmology and Physiology & Biophysics, Mount Sinai School of Medicine, New York, NY.
Correspondence to C. Rodriguez-Sargent, PhD, Research Services (151), San Juan Veterans Medical Center, One Veterans Plaza, San Juan, PR 00927-5800. E-mail rodriguez-sargent, c@san juan.
We assessed components of lenticular short-circuit current in adult hypertensive Dahl salt-sensitive rats (DS) during chronic control (0.4% sodium) versus high (3% sodium) dietary NaCl intake begun at the age of 4 weeks until rats were studied. We also evaluated the influence of barium, a potassium channel blocker, and ouabain, a specific inhibitor of Na+,K+-ATPase activity, by adding them to the anterior lens surface, thus measuring barium-sensitive, ouabain-sensitive, and barium- and ouabain-insensitive short-circuit currents. During control NaCl intake, short-circuit current in DS and their control group, Dahl salt-resistant rats (DR), did not differ significantly. DS were subclassified into cataract-prone rats and rats unlikely to develop cataracts on the basis of their initial pressor response to the change from a normal to high NaCl diet during the first weeks of age. Although only transparent lenses were studied, total lens short-circuit current was already markedly decreased in the cataract-prone subgroup compared with DS unlikely to develop cataracts and control DR. This was in sharp contrast to the increase in short-circuit current previously reported in Sprague-Dawley rats and now observed in control DR in response to high dietary NaCl. The decrease in lens short-circuit current in cataract-prone rats was associated with lower absolute values of barium- and ouabain-sensitive short-circuit currents as well as with low barium- and ouabain-insensitive short-circuit current. Although the barium- and ouabain-sensitive components of the short-circuit current were similar in DS unlikely to develop cataracts and DR, the barium- and ouabain-insensitive component of the short-circuit current was lower in DS unlikely to develop cataracts than values in DR. Interestingly, this component of lens short-circuit current also increased in DR during chronic high NaCl, whereas the opposite change occurred in cataract-prone DS and DS unlikely to develop cataracts. Thus, the barium- and ouabain-insensitive short-circuit current may be a mechanism that protects the normal lens from developing cataracts. Possible candidates for this short-circuit current component are voltage-dependent potassium channels, calcium-activated potassium channels, or both. Our studies show altered lens short-circuit current in response to high NaCl intake in cataract-prone DS and suggest the possibility of altered lens potassium transport during sustained hypertension but before loss of lens transparency.
Key Words: cataract • lens, crystalline • potassium channels • sodium chloride, dietary
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