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J C Cheney

Publications and source records attributed to J C Cheney.

6 recordsLinked to original sources
PubMed1984

Copper efflux kinetics from rat hepatocytes.

The kinetics of copper efflux from rat hepatocytes were determined to further characterize the hepatic Cu(II) transport system. Efflux was biphasic. Net efflux was rapid for 1-5 min, and 35-45% of preloaded copper was lost by 40 min. Efflux was negligible after 40 min. The retained percentage was independent of the preloading concentration, but the total amount of intracellular copper that was available for efflux gradually decreased as the duration of the preloading period increased. Unlabeled extracellular Cu(II) displaced 64Cu from intracellular pools, but exchange with intracellular Cu was not required for uptake. Zinc also displaced copper but less effectively than copper. This implies some specificity in intracellular binding components. No transstimulation of uptake or efflux was detected. Copper efflux was strictly passive. Extracellular Cu(II) decreased the rate of efflux and preloading inhibited Cu(II) uptake. Metabolic inhibitors had no effect on the rate or total amount of 64Cu efflux, and significant efflux occurred at 4 degrees C. Moreover, when a steady state was attained at the end of a preloading period, the effective intracellular concentration of free copper approximated the Cu(II) concentration in the extracellular medium. By use of this estimate for the intracellular concentration of free copper, efflux kinetic parameters were obtained from initial (1-min) rate data (Km = 5.5 +/- 0.8 microM; Vmax = 1.1 +/- 0.1 nmol X min-1 X mg prot-1). These parameters are similar to those obtained for Cu(II) uptake, and the saturation kinetics observed are consistent with specific facilitated efflux by this copper transport system.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Mobilization of copper(II) from plasma components and mechanisms of hepatic copper transport.

The effects of plasma Cu(II) ligands on the kinetics of Cu(II) transport by rat liver parenchymal cells were determined to examine how Cu(II) is mobilized from plasma and transported into liver cells. Albumin markedly inhibited Cu(II) uptake at Cu(II)-to-albumin molar ratios of 3:1 or less. Kinetic analyses showed that albumin inhibits Cu(II) uptake by reducing the concentration of free Cu(II) in solution. Under conditions of excess albumin to Cu(II), histidine facilitated albumin-inhibited uptake of Cu(II). Threonine, glutamine, and most other amino acids were without effect. Moreover, the facilitation effect of a low-molecular-weight plasma fraction (less than or equal to 5,000) was largely accounted for by its histidine concentration. The tripeptide Gly-His-Lys also inhibited Cu(II) uptake into hepatocytes by the same mechanism as albumin. The inhibitory effects of albumin and Gly-His-Lys were additive with or without histidine. The active species in the Cu(II), albumin, and histamine mixtures was shown to be the His2Cu(II) complex. Vmax for this complex was identical to the Vmax for free Cu(II), but the Km was slightly higher [15 microM vs. 11 microM for free Cu(II)]. Concurrent determinations of [3H]-histidine and 64Cu(II) uptake showed that histidine was not transported with Cu(II) from His X Cu(II) or His2Cu(II) complexes. The data are consistent with histidine mobilizing Cu(II) from albumin by competing for Cu(II), interaction of the His2Cu(II) complex with the putative hepatic copper transport protein, and transport of copper as free ionic copper.

Amino Acids↗
PubMed1983

Copper transport kinetics by isolated rat hepatocytes.

Uptake and efflux of 64Cu were examined to determine whether hepatic parenchymal cells exhibit the kinetic criteria of a specific transport system for copper and related trace metals. Saturation kinetics were clearly indicated by both v versus [Cu] and 1/v versus 1/[Cu] plots (Km = 11 +/- 0.6 microM and Vmax = 2.7 nmol Cu X min-1 X mg prot-1). Identical results were obtained by cold-copper analyses, and contributions from simple diffusion or nonspecific binding were not detected. Virtually all of the accumulated 64Cu was intracellular by 0.5 min (the initial velocity period), with approximately 40% in the cytosolic fraction. Several related trace metals inhibited 64Cu uptake, but Ni(II) at a 10:1 molar excess did not. Zn(II) acted as a simple competitive inhibitor of 64Cu uptake (Ki = 16 microM). Efflux from preloaded cells was biphasic, with an initial rapid phase of approximately 5 min. Approximately 35% of preloaded 64Cu was transported out of the cells by 40 min, and little efflux occurred thereafter. Thus, hepatocytes exhibit saturation kinetics, competition by related substrates, and countertransport criteria of specific facilitated transport. A wide variety of metabolic inhibitors have no effect on 64Cu uptake under the same conditions that inhibit the active transport of bile acids. Specific inhibitor tests for electrogenic coupling were also negative. Because the identical kinetic parameters were obtained for free 64Cu and the 1:1 64Cu-histidine complex, it is inferred that copper is probably transported as the free ion. Cells incubated with greater than or equal to 10 microM 64Cu showed a net loss of copper after 40- to 60-min incubation, which may involve specific hepatic mechanisms in copper homeostasis.

Animals↗
PubMed1981

The effect of phorbol esters on the proliferation of C3H-10T 1/2 mouse fibroblasts: consideration of both stimulatory and inhibitory effects.

TPA stimulates cell cycle activation in both serum-deprived and density-inhibited cultures. The cells reestablish cycle arrest after no more than one generation, and addition of fresh drug produces no further response. However, cells freshly trypsinized can respond with a series of repetitive generations resulting in 3.5-4.0 population doublings over 72 hrs. In kinetic pulse experiments TPA enhanced 3H-thymidine incorporation in density-inhibited cells stimulated by fresh serum but only after markedly suppressing incorporation 8-13 hrs after serum stimulation. When cells arrested by serum deprivation were pretreated with TPA, fresh serum stimulation led to initiation of 3H-TdR incorporation 5 hrs earlier than untreated controls. However, TPA addition at the time of serum stimulation did not lead to a suppression at 8-13 hrs, whereas enhancement was observed during peak incorporation times regardless of whether the cells were pretreated with TPA during serum deprivation. The results support the concept that there can exist within G1 multiple states of responsiveness to phorbol esters. These pharmacologically induced states may be correlated with corresponding physiological states of the G1 phase of cell cycle.

Animals↗
PubMed1981

Cell cycle activation and ouabain-sensitive ion movements of 3T3 and C3H-10T1/2 fibroblasts.

The introduction of either PGF2 alpha-(10(-7) M) or TPA (10(-7) M) stimulated, ouabain-sensitive 86Rb+ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF2 alpha at these concentrations stimulated the incorporation of 3H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na+/K+ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-10T1/2 cells there were parallel increases in 3H-TdR incorporation and ouabain-sensitive 86Rb+ influxes with 10(-7) M TPA, whereas PGF2 alpha stimulated a significant increase in 3H-TdR incorporation in 3T3-4 but not C3H-10T1/2 cells and only marginal increases in ouabain-sensitive 86Rb+ influx in both. Therefore, although there appears to be a close correlation between Na+/K+ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF2 alpha cannot be confirmed.

Animals↗