Na + /Ca 2+ Exchanger

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Abstract
The Na + /Ca 2+ exchanger regulates intracellular calcium ([Ca 2+ ] i ), and attenuation of Na + /Ca 2+ exchange by oxidative stress might lead to dysregulation of [Ca 2+ ] i . We have shown that the Na + /Ca 2+ exchanger differs functionally and at the amino acid level between salt-sensitive and salt-resistant rats. Therefore, the purpose of these studies was to determine how oxidative stress affects the activities of the 2 Na + /Ca 2+ exchangers that we cloned from mesangial cells of salt-resistant (RNCX) and salt-sensitive (SNCX) Dahl/Rapp rats. The effects of oxidative stress on exchanger activity were examined in cells expressing RNCX or SNCX by assessing 45 Ca 2+ uptake (reverse mode) and [Ca 2+ ] i elevation (forward mode) in the presence and absence of H 2 O 2 and peroxynitrite. Our results showed that 45 Ca 2+ uptake in SNCX cells was attenuated at 500 and 750 μmol/L H 2 O 2 (63±12% and 25±7%, respectively; n=16) and at 50 and 100 μmol/L peroxynitrite (47±9% and 22±9%, respectively; n=16). In RNCX cells, 45 Ca 2+ uptake was attenuated at only 750 and 100 μmol/L H 2 O 2 and peroxynitrite (61±9% and 63±6%, respectively; n=16). In addition, the elevation in [Ca 2+ ] i was greater in SNCX cells than in RNCX cells in response to 750 μmol/L H 2 O 2 (58±5.5 vs 17±4.1 nmol/L; n=13) and 100 μmol/L peroxynitrite (33±5 vs 11±6 nmol/L; n=19). The enhanced impairment of SNCX activity by oxidative stress might contribute to the dysregulation of [Ca 2+ ] i that is found in this model of salt-sensitive hypertension.

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