Altered Mg2+ transport across liver plasma membrane from streptozotocin-treated rats.
Type-I diabetes is associated with a decrease in magnesium content in various tissues, including liver. We have reported that hepatocytes from streptozotocin-injected rats have lost the ability to accumulate Mg2+ following hormonal stimulation. To assess whether the defect is inherent to the Mg2+ transport mechanism located in the hepatocyte cell membrane, plasma membrane vesicles were purified from diabetic livers. Diabetic plasma membranes do not retain intravesicular Mg2+ as tightly as vesicles purified from livers of age-matched non-diabetic rats. In addition, the amount of intravesicular Mg2+ these vesicles exchange for extravesicular Na+ or Ca2+ is 2-3-fold larger than in non-diabetic vesicles. The partition of Ca2+/Mg2+ and Na+/Mg2+ exchange mechanisms in the apical and basolateral domains of liver plasma membrane is maintained under diabetic conditions, although the Na+/Mg2+ exchanger in diabetic basolateral membranes has lost the ability to operate in reverse and favor an accumulation of extravesicular Mg2+ within the vesicles in exchange for entrapped Na+. These data indicate the occurrence of a major alteration in Mg2+ transport across the hepatocyte membrane, which can explain, at least in part, the decrease in liver magnesium content observed in diabetic animals and patients.
Cefaratti
Christie
C
Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4970, USA.
McKinnis
Amy
A
Romani
Andrea
A
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D051381:Rats; D011917:Rats, Inbred Lew; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D013311:Streptozocin
D013311:Streptozocin; D012964:Sodium; D008274:Magnesium; D002118:Calcium