In a typical mammalian cell about 95% of the ATP used is produced in the mitochondria. the mitochondrion is also noted for possessing an elaborate system for transporting Ca2+. The system consists of 3 or perhaps 4 separate mechanisms: an influx mechanism (uniporter) having an extremely high Vmax, two separate efflux mechanisms, and a permeability transition which may or may not be involved in Ca2+ transport in vivo. Our long term goal is to determine the physiological role or roles which this complex system serves. A number of possible roles for this system have been suggested in the past, but only two have survived the assaults of earlier data: (1) That mitochondria control matrix [Ca2+] so as to regulate the rate of oxidative phosphorylation at least partly through control of three Ca2+-sensitive dehydrogenases, and (2) That mitochondria sequester Ca2+ in order to protect the cytosol from the effects of hypercalcemia in damaged cells.
The specific aims of the current proposal are designed: (1) To test the """"""""weak link"""""""" of the first proposed role above by determining if mitochondria can sequester Ca2+ from short pulses like those generated by hormones in vivo and if so, how the pulses' shape, intensity and periodicity affect the amount of Ca2+ taken up. (2) To evaluate Ca2+ effects on oxidative phosphorylation at intramitochondria loci other than the dehydrogenases by measuring Ca2+ effects on degrees of coupling and efficiencies of separate parts of the process. This will involve application of a new approach developed in earlier years of this grant. Some of the separate parts of the process to be studied are: generation of the electrochemical proton gradient, leakage of protons from the gradient and phosphorylation at the ATPase. (3) To evaluate a new possible role that one of the efflux mechanisms may serve a toxicological function in clearing the mitochondrion of unwanted ions preparatory to their clearance from the cell. It is becoming increasingly apparent that because of its vital role in ATP production, failure of the mitochondrial systems and loss of Ca2+ control are common irreversible steps leading to cell death. Without a better understanding of its physiological role or roles, the consequences of malfunctions of the Ca2+ transport system for the mitochondrion, the cell and the organism cannot be completely assessed.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM035550-07
Application #
3288496
Study Section
Physical Biochemistry Study Section (PB)
Project Start
1985-08-30
Project End
1996-03-31
Budget Start
1993-04-01
Budget End
1994-03-31
Support Year
7
Fiscal Year
1993
Total Cost
Indirect Cost
Name
University of Rochester
Department
Type
Schools of Dentistry
DUNS #
208469486
City
Rochester
State
NY
Country
United States
Zip Code
14627
Gavin, C E; Gunter, K K; Gunter, T E (1999) Manganese and calcium transport in mitochondria: implications for manganese toxicity. Neurotoxicology 20:445-53
Sparagna, G C; Gunter, K K; Sheu, S S et al. (1995) Mitochondrial calcium uptake from physiological-type pulses of calcium. A description of the rapid uptake mode. J Biol Chem 270:27510-5
Gunter, T E; Gunter, K K; Sheu, S S et al. (1994) Mitochondrial calcium transport: physiological and pathological relevance. Am J Physiol 267:C313-39
Baysal, K; Jung, D W; Gunter, K K et al. (1994) Na(+)-dependent Ca2+ efflux mechanism of heart mitochondria is not a passive Ca2+/2Na+ exchanger. Am J Physiol 266:C800-8
Sparagna, G C; Gunter, K K; Gunter, T E (1994) A system for producing and monitoring in vitro calcium pulses similar to those observed in vivo. Anal Biochem 219:96-103
Gunter, T E (1994) Cation transport by mitochondria. J Bioenerg Biomembr 26:465-9
Gunter, K K; Gunter, T E (1994) Transport of calcium by mitochondria. J Bioenerg Biomembr 26:471-85
Sheu, S S; Jou, M J (1994) Mitochondrial free Ca2+ concentration in living cells. J Bioenerg Biomembr 26:487-93
Gavin, C E; Gunter, K K; Gunter, T E (1992) Mn2+ sequestration by mitochondria and inhibition of oxidative phosphorylation. Toxicol Appl Pharmacol 115:1-5
Gavin, C E; Gunter, K K; Gunter, T E (1991) Mn2+ transport across biological membranes may be monitored spectroscopically using the Ca2+ indicator dye antipyrylazo III. Anal Biochem 192:44-8

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