An hypothesis for preconditioning and heat shock proteins: A model for elucidating damage pathways in the 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.

Physiological blocking of the mechanisms of cold death: theoretical and experimental considerations

The cold inhibited functions of skin thermoreceptors, of the thermoregulation centre, and the respiration centre during deep hypothermia can be restored without rewarming the body. The methods used were developed to test the hypothesis that during deep hypothermia calcium ion concentration [Ca(2+)](i) in the cytoplasm increases. This causes a perturbation of cell metabolism, the impairment of cell membrane function that cause the inhibition of cell functioning, resulting in cell death. Such an increase in [Ca(2+)](i) most likely would result from an energy deficit in a deeply cooled cell, which would compromise the processes that maintain the [Ca(2+)](i) at about 10(-7) M. These processes require large amounts of energy since they occur against a large concentration gradient. With the use of EDTA the extracellular concentration of Ca(2+) has been lowered by 15-27%, so reducing the concentration gradient for Ca(2+) between the cell and the medium and in consequence facilitated the process the extrusion of cell Ca(2+).During a period of cooling, sufficient to impair normal functioning, the experimental lowering of blood Ca(2+) allowed the restoration of normal function without the need to rewarm. In such cases the animals survived after cooling the body to temperatures at which they would normally have succumbed. The data presented support the stated hypothesis that the impairment of cellular function in mammals by low temperatures is the result of an uncorrected rise in [Ca(2+)](i).

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.