Extracellular K+ and protection against cellular damage in the rat heart

Protection against cellular damage in the rat heart by iodoacetate

In this comparative study, rat hearts were perfused at 37 degrees C with three clearly defined protocols: the Ca2+ paradox, the O2 paradox, and with 20 mM caffeine. Each protocol involved an initial priming (Ca2+o depletion or anoxia; stage 1) and subsequent full activation (Ca2+o repletion, caffeine or reoxygenation; stage 2) of the damage system of the sarcolemma. Iodoacetate (1 mM) provided complete protection in the O2 paradox and over 80% protection in the Ca2+ paradox and caffeine protocols against creatine kinase release when present throughout the experiment (P < 0.001). Almost identical protection was found when iodoacetate was present only in stage 2 (P < 0.001). However, it was concluded that iodoacetate had limited protective effects when present only in stage 1 in any of the three protocols and that its action is to inhibit the activity of the transsarcolemma damage system in stage 2 when it has been activated in stage 1. It is suggested that iodoacetate interacts with thiol groups on the damage system of the sarcolemma.

Protection against cellular damage in the rat heart by hyperosmotic solutions

In this comparative study, rat hearts were perfused at 37 degrees C with three clearly defined protocols: the Ca2+ paradox, the O(2) paradox, and with 20 mM caffeine. Each protocol involved an initial priming (Ca(2+)(0) depletion or anoxia; stage 1) and subsequent full activation (Ca(2+)(0) repletion, caffeine or reoxygenation; stage 2) of the damage system of the sarcolemma. Creatine kinase release in stage 2 was completely inhibited (P < 0.001) in all three protocols when 420 mOsm was added to the perfusion medium throughout the experiments, or only during stage 1, or only during stage 2. Increasing the perfusion pressure in the Ca2+ paradox significantly (P < 0.001) exacerbated creatine kinase release, although this was still completely inhibited at 28 degrees C. Amiloride (1 mM) inhibited creatine kinase release completely at 40 cm of water pressure but only some 50% at 80 cm of water pressure. It is suggested that the transmembrane damage system needs to be uncoupled or deactivated by modifying its relationship with the cytosol or with the underlying cytoskeleton by hyperosmotic cell shrinkage for only one of the stages in all three protocols to block the damage pathway. Increased perfusion pressure has the opposite effect and exacerbates damage.

Protection against cellular damage in the perfused rat heart by lowered pH

In this comparative study, rat hearts were perfused at 37 degrees C with three clearly defined protocols: the Ca2+ paradox, the O2 paradox and with 20 mM caffeine. Each protocol involved an initial priming (Ca2+(o) depletion or anoxia; stage 1) and subsequent full activation (Ca2+(o) repletion or reoxygenation; stage 2) of the damage system of the sarcolemma. Creatine kinase release in stage 2 was completely inhibited (P < 0.001) in all three protocols when pH was reduced to 6.5 throughout the experiments, or only during stage 1, or only during stage 2. The inhibitor of the Na+/H+ antiporter, amiloride (1 mM), completely prevented creatine kinase release in the Ca2+ paradox (P < 0.001) and markedly reduced damage in the caffeine protocol. Amiloride had no significant effect on creatine kinase release in the O2 paradox. The possible role of Na+(i) was studied in the caffeine protocol: ouabain (5 x 10(-6) M) had little effect whereas substitution of choline for Na+ in the perfusion medium reduced creatine kinase release by about 50%. It is suggested that the same damage system is activated in stage 1 in all three protocols and that a key event is the intracellular production of H+ which are exported via Na+(o)/H(i) exchange. Prevention of H+ efflux by lowered pH(o), even during stage 2, protected against creatine kinase release. The possible role of Na+ movements in the genesis of sarcolemma damage is discussed.