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.