NA/CA2 EXCHANGE AND CAI IN THE PROXIMAL TUBULE

Project: Research project

Description

We propose to test two hypotheses: One, in the rat proximal
tubule, Na+/Ca2+ exchange (Na/Ca) regulates, in part, the
concentration of cytosolic Ca2+ (Ca/i). Two, in the rat proximal
tubule, anoxia alters the homeostatic interdependence of Ca2+
and Na+. This alteration reverses Na/o-dependent Ca2+ efflux to
Ca/o-dependent Ca2+ influx. To achieve this purpose, four aims
are outlined: One, to investigate the modulation of Ca/i by
fluctuations in the electrochemical gradients of Na+ and Ca2+
delta uNa+ and delta uCa2+). Two, to examine the direction of
the fluxes of Na+ and Ca2+ evoked by fluctuations in delta uNa+
and delta uCa2+ in the intact rat proximal tubule. Three, to
examine the contribution from intracellular organelles to the
regulation of Ca/i by Na+. Four, to define the alterations in
Na/Ca exchange in the anoxic rat proximal tubule. The basis for
these investigations are theoretical and empirical. Based on a
thermodynamic analysis, it is proposed that delta uNa+ and delta
uCa2+ are forces oriented from the outside of the cell to the
inside of the cell. These two forces drive Na+ influx in exchange
for Ca2+ efflux and Ca2+ influx in exchange for Na+ efflux,
respectively (Na/CA exchange). The orientation of Na/Ca
exchange may change in pathological states, caused by changes in
the magnitude of one force relative to the magnitude of the other
force. These changes may have profound effects on Ca/i
homeostasis. This notion has been confirmed, in part, in our
laboratory. We showed that fluctuations of delta uNa+ and delta
uCa2+ change Ca/i in rat proximal tubules in accord with the
thermodynamic model. These investigations support the idea that
Ca/i is regulated by Na/Ca exchange. We propose to extend this
work, by measuring Ca/i, using aequorin and the fluxes of 45Ca
and 22Na in rat proximal tubules. In addition, we propose to study
the effect of anoxia on Na/Ca exchange. It is proposed that in
anoxia, alterations in Ca/i may be caused, in part, by the
prevalence of the force delta uCa2+ over delta uNa+. Thus far,
the role of Na/Ca exchange in Ca/i and Na/i homeostasis has been
ignored, in part because of the assumption that Na/Ca exchange
may not operate in nonexcitable cells. In this proposal we provide
evidence to the contrary. The proposed work, should also improve
our understanding of the pathogenesis of alterations in Ca/i
homeostasis in the proximal tubule in anoxia. These alterations
may participate in ischemic renal injury.
StatusFinished
Effective start/end date4/1/882/29/92

Funding

  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health: $121,256.00

Fingerprint

Aequorin
Organelles
Homeostasis
Kidney
Wounds and Injuries
Hypoxia
Direction compound

ASJC

  • Medicine(all)