CELLULAR AND TISSUE FUNCTION 



205 



rate. Phenol red accumulation is also not depressed (Shideman and Rene, 

 1951 b), although in isolated flounder tubules it is suppressed by 10-20 roM 

 malonate (Forster and Goldstein, 1961). It was claimed that there is a cor- 

 relation between succinate oxidase activity and transport in different spe- 

 cies. Clearance studies with glucose and phosphate show that there is little 

 effect of malonate on their transport: e.g., when p-aminohippurate trans- 

 port is inhibited 73%, glucose Tm is decreased only 10%. On the other 

 hand, Malvin (1956) reported that malonate quite definitely depresses the 

 phosphate Tm, although no data were given. Since malonate interferes 

 with the uptake of inorganic phosphate in kidney homogenates, it was 

 concluded that malonate in some manner suppresses the esterification of 

 phosphate during its transport. 



Fig. 1-18. Effects of inhibitors on the slice/medium (S/M) ratio 

 for p-aminohippurate in kidney shces. DNP = 2,4-dinitrophenol, 

 FA = fluoroacetate, lA = iodoacetate, DHA = dehydroacetate, 

 CN = cyanide, and F = fluoride. (Modified from Farah and 

 Rennick, 1956.) 



Renal electrolyte transport is disturbed by malonate (Mudge, 1951). 

 Rabbit renal cortex slices were leached for 2.5 hr in 0.15 M NaCl, this 

 lowering the tissue K+ concentration and reducing the endogenous respir- 

 ation. The slices were then incubated for 30 min in medium containing 

 10 mM K+, 10 mM acetate, NaCl to provide a constant osmotic pressure, 

 and phosphate buffer, during which time K+ enters the cells. Malonate at 

 50 mM almost completely blocks this return of K+ into the cells and re- 

 verses the movement of water (see accompanying tabulation). The Na+ 

 changes are not so significant because the substitution of divalent anions 

 for chloride increases the external, and presumably the internal, Na+ con- 

 centration. If fresh slices are treated with malonate, a loss of cell K+ and 



