EFFECT OF HYPOTHERMIA ON INTRACELLULAR CA2-GLUCONATE PRESERVATION SOLUTION( IN RABBIT RENAL TUBULES SUSPENDED IN UW)

Altered cellular calcium (Ca) homeostasis may be important in mediatin g hypothermic injury in preserved kidneys. in this study the effect of hypothermic (5 degrees C) storage on ionized intracellular Ca concent ration ([Ca](i)) in rabbit tubules was examined using Indo-1. Tubules were stored up to 250 min in UW-gluconate solution containing either 0 .0, 0.5, 1.5, or 5.0 mM Ca (yielding about 3.6, 62, 371, and 1,010 mu M ionized solution Ca (Ca2+) at 5 degrees C, respectively). [Ca](i) in creased to about 1,600 nM within 1 min after suspension in UW solution followed by a decrease in [Ca](i) during the subsequent 60 min in all groups, suggesting mitochondrial Ca sequestration. Thereafter, [Ca](i ) either 1) increased in tubules incubated with 1.5 and 5.0 mM Ca to l evels greater than 2,500 nM; 2) decreased to about 800 nM in tubules i ncubated with 0.5 mM Ca and then remained stable; or 3) continued to d ecrease in tubules incubated with 0.0 mM added Ca to reach an apparent steady-state concentration of about 175 nM after 180 min of incubatio n. The early spike in [Ca](i) was unaffected by adding EGTA. (solution Ca2+ = 50 nM). Ryanodine eliminated the [Ca](i) spike, indicating tha t cooling in UW-gluconate solution caused release of endoplasmic retic ulum Ca. This study shows that [Ca](i) initially increases after expos ure to UW-gluconate solution and appears to be transiently buffered th rough intracellular, probably mitochondrial, sequestration. Saturation of cellular buffer mechanisms resulted in a sustained dependence of [ Ca](i) on extracellular Ca2+. These results support the hypothesis tha t the effect of Ca on kidney viability is related to solution-induced alterations in [Ca](i). (C) 1996 Academic Press. Inc.