Calcium paradox in canine kidneys

Isolated perfusion of the heart with a Ca2+-free perfusate followed by a Ca2+-containing perfusate causes dramatic alterations in the physiology and biochemistry of the tissue, a phenomenon known as the calcium paradox. A similar paradoxical effect of Ca2+ has also been reported to occur in the kidney. In this study an attempt was made to reproduce the calcium paradox in canine kidneys and to characterize more fully its metabolic consequences. Canine kidneys were perfused with Krebs-Henseliet bicarbonate buffer free of Ca2+ for 30 min followed by perfusion with Ca2+ (1.5 mM). Unlike previously reported results no sudden decrease in flow was there a Ca2+-related sharp rise in rate of release of lactic dehydrogenase. In addition, we found no significant change in the level of tissue adenine nucleotides or functionality of isolated mitochondria. It is concluded that there is no calcium paradox in canine kidney under these conditions and it is suggested that the Ca2+ paradox may be characteristics only of muscle tissue that can undergo Ca2+-dependent contraction.