Stimulation of glycine catabolism in isolated perfused rat liver by calcium mobilizing hormones and in isolated rat liver mitochondria by submicromolar concentrations of calcium.

M Jois,B Hall,J T Brosnan

doi:10.1016/s0021-9258(19)40004-5

M Jois, B Hall + Show 1 more

Open Access

https://doi.org/10.1016/s0021-9258(19)40004-5

Copy DOI

Abstract

Glucagon stimulates flux through the glycine cleavage system (GCS) in isolated rat hepatocytes (Jois, M., Hall, B., Fewer, K., and Brosnan, J. T. (1989) J. Biol. Chem. 264, 3347-3351. In the present study, flux through GCS was measured in isolated rat liver perfused with 100 nM glucagon, 1 microM epinephrine, 1 microM norepinephrine, 10 microM phenylephrine, or 100 nM vasopressin. These hormones increased flux through GCS in perfused rat liver by 100-200% above the basal rate. The possibility that the stimulation of flux by adrenergic agonists and vasopressin is mediated by increases in cytoplasmic Ca2+ which in turn could regulate mitochondrial glycine catabolism was examined by measuring flux through GCS in isolated mitochondria in the presence of 0.04-2.88 microM free Ca2+. Flux through GCS in isolated mitochondria was exquisitely sensitive to free Ca2+ in the medium; half-maximal stimulation occurred at about 0.4 microM free Ca2+ and maximal stimulation (7-fold) was reached when the free Ca2+ in the medium was 1 microM. The Vmax (nanomoles/mg protein/min) and Km (millimolar) values for the flux through GCS in intact mitochondria were 0.67 +/- 0.16 and 20.66 +/- 4.82 in the presence of 1 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid and 3.28 +/- 0.76 and 10.98 +/- 1.91 in presence of 0.5 microM free Ca2+, respectively. The results show that the flux through GCS is sensitive to concentrations of calcium which would be achieved in the cytoplasm of hepatocytes stimulated by calcium-mobilizing hormones.

Highlights

In the present study, flux through GCS was measured in isolated rat liver perfused with 100 nM glucagon, 1 KM epinephrine
The possibility that the stimulation of flux by adrenergic agonists and vasopressin is mediated by increases in cytoplasmic Ca2+ which in turn could regulate mitochondrial glycine catabolism was examined by measuring flux through GCS in isolated mitochondria in the presence of 0.04-2.88 MM free Ca2+
Flux through GCS in isolated mitochondria was exquisitely sensitive to free Caa+ in the medium; half-maximal stimulation occurred at about 0.4 MM free Ca2+ and maximal stimulation (7-fold) was reached when the free Ca2+ in the medium was 1 PM

Summary

Mitochondria by Submicromolar Concentrations of Calcium*

Glucagon stimulates flux through the glycine cleavage system (GCS) in isolated rat hepatocytes Flux through GCS was measured in isolated rat liver perfused with 100 nM glucagon, 1 KM epinephrine,. 1 pM norepinephrine, 10 pM phenylephrine, or 100 nM vasopressin These hormones increased flux through GCS in perfused rat liver by lOO-200% above the basal rate. The possibility that the stimulation of flux by adrenergic agonists and vasopressin is mediated by increases in cytoplasmic Ca2+ which in turn could regulate mitochondrial glycine catabolism was examined by measuring flux through GCS in isolated mitochondria in the presence of 0.04-2.88 MM free Ca2+. In the present study we show that epinephrine, norepinephrine, phenylephrine, and vasopressin stimulate flux through GCS in isolated perfused rat liver

AND METHODS

Mitochondria were isolated from livers obtained from male

AND DISCUSSION

PHENYLEPHRINE i