Subcellular changes in rat hearts perfused with potassium-free medium

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Abstract
The Ca binding and uptake activities of mitochondria from hearts perfused with K-free medium for 5-20 min were increased, but those for microsomes were depressed. Total ATPase activity in these subcellular fractions from K-depleted hearts did not change. Ultrastructural examination of the hearts perfused with K-free medium showed dilated sarcoplasmic reticulum within 5 min but 14-15 min of K-free perfusion caused contracted sarcomeres and swollen mitochondria. Contractile force of the isolated rat heart perfused with K-free medium showed an immediate but transient decline followed by the development of contractile failure leading to a complete cessation within 10-11 min. A marked increase in the resting tension was seen within 14-15 min of K-free perfusion. A biphasic but complete recovery of the contractile force was seen in K-depleted hearts upon reperfusion with normal medium, provided the time for K-free perfusion was less than 8 min. The inability of hearts to recover their contractile force after 10-20 min K-free perfusion was associated with irreversible changes in the Ca accumulating activities of the subcellular fractions. The occurrence of an intracellular Ca overload due to K-free perfusion appears to inflict an irreversible damage to the structure and function of the myocardium.