Glucagon stimulation of ruthenium red-insensitive calcium ion transport in developing rat liver.
The maturation of glucagon-stimulated Ruthenium Red-insensitive Ca2+-transport activity was determined in livers of rats ranging in age from 5 days preterm to 10 weeks of adult life. Previous indications are that this activity is confined to vesicles derived mainly from the endoplasmic reticulum. Perinatal-rat liver contains near-adult values of Ruthenium Red-insensitive Ca2+-transport activity, and exhibits large transient increases in the rate of this activity at two stages of development, immediately after birth, and at 2-5 days after birth. The administration of glucagon to foetal rats, at developmental stages after 19.5 days of gestation (2.5 days before birth), results in a large stable increase (greater than 100%) of Ca2+-transport activity in a subsequently isolated 'heavy' microsomal fraction. That this fraction was enriched in vesicles derived from the rough endoplasmic reticulum was indicated by both an electron-microscopic examination and a marker-enzyme analysis of the subcellular fractions. The administration of glucagon into newborn animals only hours old does not enhance further the initial rate of Ca2+-transport activity, and from day 1 to 10 weeks after birth the administration of the hormone results in the moderate enhancement of Ca2+ transport. Experiments with cyclic AMP and inhibitors of phosphodiesterase activity suggest that cyclic AMP plays a key role in the enhancement by glucagon of Ruthenium Red-insensitive Ca2+ transport, and arguments are presented that this transport system has an important metabolic role in the redistribution of intracellular Ca2+ in liver tissue.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D012428:Ruthenium / Q000494:pharmacology*; D012430:Ruthenium Red / Q000494:pharmacology*; D013268:Stimulation, Chemical; D013347:Subcellular Fractions / Q000378:metabolism
D010726:Phosphodiesterase Inhibitors; D012430:Ruthenium Red; D003994:Bucladesine; D012428:Ruthenium; D005934:Glucagon; D002118:Calcium