Subcellular calcium and magnesium mobilization in rat liver stimulated in vivo with vasopressin and glucagon.
The total Ca2+ content of the endoplasmic reticulum and the total Ca2+ and Mg2+ content of mitochondria were determined by electron probe microanalysis of rat liver rapidly frozen in vivo following brief (5-15 s) stimulation with vasopressin or prolonged (10-12 min) stimulation with vasopressin + glucagon. Brief vasopressin injection into the anterior mesenteric vein released 1.8 +/- 0.3 (S.D.) mmol of Ca2+/kg dry weight, from the rough endoplasmic reticulum (p less than 0.01), reducing Ca2+ content of the endoplasmic reticulum from 4.4 +/- 0.2 (S.E.) (controls) to 2.6 +/- 0.2 mmol of Ca2+/kg dry weight. Following vasopressin injection, endoplasmic reticulum Ca2+ was also significantly (p less than 0.025) lower than that in brief sham injected animals (3.5 +/- 0.2 mmol/kg dry weight). Mitochondrial Ca2+ was between 1.0 and 2.3 (+/-0.2) mmol/kg dry weight of mitochondrion, under all conditions studied, and no significant differences were observed. Both hormonal and brief sham injection into the anterior mesenteric vein increased mitochondrial Mg2+ from 42 (+/-0.8) to 49 (+/-1.8) mmol/kg dry weight (p less than 0.05). Hormonal stimulation of Mg2+ uptake was further confirmed by injection of vasopressin + glucagon into the jugular vein (to avoid any stimulation of the liver by the anterior mesenteric vein injection itself); mitochondrial Mg2+ increased from 43 (+/-0.9) (10-min sham) to 57 (+/-1.3) mmol/kg dry weight, with 10-min vasopressin + glucagon injection (p less than 0.01). These results demonstrate that hormones can release Ca2+ from the endoplasmic reticulum and modulate mitochondrial Mg2+ content in vivo without causing detectable changes in mitochondrial Ca2+.
Bond
M
M
Research Institute, Cleveland Clinic Foundation, Ohio 44106.
Vadasz
G
G
Somlyo
A V
AV
Somlyo
A P
AP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005934:Glucagon / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008854:Microscopy, Electron; D006005:Phosphorylases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism*; D014667:Vasopressins / Q000494:pharmacology*
D014667:Vasopressins; D005934:Glucagon; D006005:Phosphorylases; D008274:Magnesium; D002118:Calcium