Graduate Program Information
My Contact Information

Professor of Biochemistry and Biophysics
Ph.D. University of California at Berkeley 1966

Until recently, the rate of ATP production was thought to be determined by the rate at which ADP and phosphate (Pi) diffuse back to mitochondria. Recent evidence at the cellular and tissue levels suggests control by a novel mechanism, probably functioning through intramitochondrial [Ca2+]. 31P NMR has identified conditions in which [ADP] and [Pi] remain constant while ATP production is increased by a factor of four or more. Clearly, metabolic rate cannot be activated by increased [ADP] and [Pi] if they do not increase, and another mechanism of control is indicated. This additional mechanism is thought to involve intramitochondrial free calcium ([Ca2+]m). Therefore, it is important to determine whether enough Ca2+ can be sequestered by mitochondria under physiological conditions to serve this function of metabolic mediator (1).

Under physiological conditions, cytosolic free calcium ([Ca2+]c) in many tissues remains low (80 to 100 nM) except during pulses or transients of [Ca2+]c. During these pulses, [Ca2+]c can become 1 µM or larger. Even liver, a non excitable tissue, may respond to hormones through a sequence of Ca2+ pulses. A typical hepatocyte response to vasopressin, for example, could be a sequence of 6 or 8 Ca2+ pulses. It is important to determine if mitochondria can sequester enough Ca2+ from such pulses to activate the Ca2+-sensitive steps of the metabolic pathways (1). Calculations based on the kinetics of known mitochondrial Ca2+ transporters suggested that they cannot sequester enough Ca2+(1). However, these kinetics were determined using buffered [Ca2+], not [Ca2+] pulses as under physiological conditions.

We built a device capable of generating Ca2+ pulses like those observed in vivo in many tissues. The [Ca2+] is controlled by a computer-controlled automatic pipetter and measured using fluorescence. We can generate [Ca2+] pulses down to durations of 0.2 - 0.3 sec. over a broad range of [Ca2+]. Using this device, we have discovered a new mechanism of Ca2+ uptake into liver mitochondria, termed the RaM ("rapid mechanism"). Controls show that the RaM mediates rapid net mitochondrial uptake from Ca2+ pulses (2). The RaM briefly displays very high Ca2+ conductivity at the beginning of a pulse; however, the RaM is rapidly closed as the [Ca2+] of the pulse increases. It is quickly "reset" by the fall in [Ca2+] between Ca2+ pulses and therefore functions at the beginning of each pulse. It is sufficiently activated by physiological concentrations of spermine to allow enough Ca2+ to be sequestered from a few pulses to stimulate ATP production. RaM-mediated metabolic signaling shows characteristics of "frequency modulation" (2). The RaM also exists in heart mitochondria; however, its characteristics in heart are quite different from those observed in liver. We believe that this newly discovered mechanism may be the most important component of the system controlling metabolic rate.

We are extending this work by: 1) Determining how hormonal control of this novel mechanism is mediated. 2) Determining its characteristics in heart mitochondria. 3) Developing faster techniques for generating Ca2+ pulses in order to measure the duration of the RaM's high conductivity period.

Control of Growth of Long Bones

With Dr. Randy Rosier of Orthopedics, we are studying the growth of long bones (3, 4) mediated by growth plate chondrocytes (GPC's). Growth plates found near both ends of long bones and are responsible for longitudinal bone growth. GPC's mature within the growth plate, from small spherical "resting cells", passing through the rapidly dividing proliferative stage to the terminal "hypertrophic phase". GPC's cause the extension of the length of long bones both by cell division and by hypertrophy of the mature cells, and secrete a matrix capable of supporting mineralization of new bone.

Recently, we have investigated the actions of parathyroid hormone related protein (PTHrp), the autocrine/pericrine factor that exerts the strongest control on the developing cells of the growth plate (3, 4). PTHrp inhibits differentiation and maturation of GPC's, causing the more mature hypertrophic chondrocytes to express a less mature "proliferative" phenotype. If maturation of the GPC's is retarded, more cell proliferation can occur and the bone can grow longer.

Earlier work has shown that PTHrp acts both through the cAMP pathway and through the IP3, DAG, Ca2+ pathway; however, most of the PTHrp effects listed above are mediated through the cAMP pathway (3, 4). Interestingly, none are mediated through the Ca2+ pathway. We have also found that PTHrp causes a chronic increase in [Ca2+]c in these cells; which, in turn, leads to a decrease in PTHrp message levels. Work is currently being performed to address this issue.

Recent Publications

Eliseev RA, Filippov G, Velos J, VanWinkle B, Goldman A, Rosier RN, Gunter TE (2007) Role of cyclophilin D in the resistance of brain mitochondria to the permeability transition. Neurobiol Aging, 28:1532-42

Gunter TE, Gavin CE, Aschner M, Gunter KK (2006) Speciation of manganese in cells and mitochondria: A search for the proximal cause of manganese neurotoxicity. Neurotoxicology, 27:765-76

Gunter KK, Aschner M, Miller LM, Eliseev R, Salter J, Anderson K, Gunter TE (2005) Determining the oxidation states of manganese in NT2 cells and cultured astrocytes. Neurobiol Aging,

Gunter KK, Aschner M, Miller LM, Eliseev R, Salter J, Anderson K, Hammond S, Gunter TE (2005) Determining the oxidation states of manganese in PC12 and nerve growth factor-induced PC12 cells. Free Radic Biol Med, 39:164-81

Eliseev RA, Vanwinkle B, Rosier RN, Gunter TE (2004) Diazoxide-mediated preconditioning against apoptosis involves activation of cAMP-response element-binding protein (CREB) and NFkappaB. J Biol Chem, 279:46748-54

Gunter TE, Yule DI, Gunter KK, Eliseev RA, Salter JD (2004) Calcium and mitochondria. FEBS Lett, 567:96-102

Gunter TE, Miller LM, Gavin CE, Eliseev R, Salter J, Buntinas L, Alexandrov A, Hammond S, Gunter KK (2004) Determination of the oxidation states of manganese in brain, liver, and heart mitochondria. J Neurochem, 88:266-80

Eliseev RA, Gunter KK, Gunter TE (2003) Bcl-2 prevents abnormal mitochondrial proliferation during etoposide-induced apoptosis. Exp Cell Res, 289:275-81

Eliseev RA, Salter JD, Gunter KK, Gunter TE (2003) Bcl-2 and tBid proteins counter-regulate mitochondrial potassium transport. Biochim Biophys Acta, 1604:1-5

Zuscik MJ, O'Keefe RJ, Gunter TE, Puzas JE, Schwarz EM, Rosier RN (2002) Parathyroid hormone-related peptide regulation of chick tibial growth plate chondrocyte maturation requires protein kinase A. J Orthop Res, 20:1079-90

Zuscik MJ, D'Souza M, Ionescu AM, Gunter KK, Gunter TE, O'Keefe RJ, Schwarz EM, Puzas JE, Rosier RN (2002) Growth plate chondrocyte maturation is regulated by basal intracellular calcium. Exp Cell Res, 276:310-9

Eliseev RA, Gunter KK, Gunter TE (2002) Bcl-2 sensitive mitochondrial potassium accumulation and swelling in apoptosis. Mitochondrion, 1:361- 370

Gunter KK, Miller LM, Aschner M, Eliseev R, Depuis D, Gavin CE, Gunter TE (2002) XANES spectroscopy: A Promising tool for toxicology: A tutorial. Neurotox., 23:127 146

Graduate students in my laboratory work toward a Ph.D. degree in the following program[s]:

Ph.D. in Biochemistry
Ph.D. in Biophysics

Ph.D. candidates in my laboratory may also be affiliated with these programs:

Contact Information

E-Mail: Thomas_Gunter@urmc.rochester.edu

Thomas E. Gunter
Department of Biochemistry and Biophysics
University of Rochester School of Medicine and Dentistry
601 Elmwood Ave, Box 712
Rochester, New York 14642

Office: Medical Center 1-5755
Telephone: (585) 275-3129; Fax: (585) 275-6007