MEMBRANE DAMAGE AND THE CA2-PARADOX IN THE PERFUSED RAT-KIDNEY()

Lactate dehydrogenase (LDH) leaks from the perfused rat kidney under t he artificial conditions of a Ca2+-paradox protocol, namely Ca2+-reple tion following a 20 minute period of Ca2+-depletion. LDH leakage was m arkedly suppressed by perfusion at 25 degrees C or with 0.1 mM dibucai ne or 2 mM lidocaine. Lidocaine inhibited leakage only during Ca2+-dep letion. Lowering the perfusion rate significantly reduced LDH escape. No LDH loss occurred if the osmotic pressure of the perfusion fluid wa s raised by 420 mOsm during either Ca2+-depletion or Ca2+-repletion. A miloride (2 mM) significantly reduced LDH leakage to 43%. Reduction of the pH of the perfusion fluid to 6.8 significantly inhibited LDH loss , and at pH 6.4 this leakage was almost completely suppressed. LDH los s was equally suppressed at pH 6.4 only during Ca2+-depletion, whereas pH 6.4 was markedly less effective when perfused only during Ca2+-rep letion. Ouabain (5 x 10(-6) M) had only a limited effect in exacerbati ng LDH leakage. Raising [K+](0) significantly protected against LDH le akage, which fell to 36% at 16 mM [K+]. These features correspond with the Ca2+-paradox of the perfused rat heart and it is suggested that: (i) a Ca2+-paradox can be produced in the rat kidney; (ii) a similar m echanism governs the release of cytosolic proteins in these two prepar ations; and (iii) the damage mechanism of the plasmalemma is a transme mbrane oxidoreductase-diaphorase molecular complex which generates Hwhen activated by Ca2+-depletion.