Membrane-Bound and cytosolic forms of heterotrimeric G proteins in young and adult rat myocardium: influence of neonatal hypo- and hyperthyroidism.
Membrane and cytosolic fractions prepared from ventricular myocardium of young (21-day-old) hypo- or hyperthyroid rats and adult (84-day-old) previously hypo- or hyperthyroid rats were analyzed by immunoblotting with specific anti-G-protein antibodies for the relative content of Gs alpha, Gi alpha/Go alpha, Gq alpha/G11 alpha, and G beta. All tested G protein subunits were present not only in myocardial membranes but were at least partially distributed in the cytosol, except for Go alpha2, and G11 alpha. Cytosolic forms of the individual G proteins represented about 5-60% of total cellular amounts of these proteins. The long (Gs alpha-L) isoform of Gs alpha prevailed over the short (Gs alpha-S) isoform in both crude myocardial membranes and cytosol. The Gs alpha-L/Gs alpha-S ratio in membranes as well as in cytosol increased during maturation due to a substantial increase in Gs alpha-L. Interestingly, whereas the amount of membrane-bound Gi alpha/Go alpha and Gq alpha/G11 alpha proteins tend to lower during postnatal development, cytosolic forms of these G proteins mostly rise. Neonatal hypothyroidism reduced the amount of myocardial Gs alpha and increased that of Gi alpha/Go alpha proteins. By contrast, neonatal hyperthyroidism increased expression of Gs alpha and decreased that of Gi alpha and G11 alpha in young myocardium. Changes in G protein content induced by neonatal hypo- and hyperthyroidism in young rat myocardium were restored in adulthood. Alterations in the membrane-cytosol balance of G protein subunits associated with maturation or induced by altered thyroid status indicate physiological importance of cytosolic forms of these proteins in the rat myocardium.
Novotny
J
J
Institute of Physiology, Academy of Sciences of the Czech Republic, Prague.
Bourová
L
L
Kolár
F
F
Svoboda
P
P
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D003600:Cytosol / Q000201:enzymology*; D020962:Heterotrimeric GTP-Binding Proteins / Q000032:analysis*; D006980:Hyperthyroidism / Q000139:chemically induced / Q000201:enzymology* / Q000473:pathology; D007037:Hypothyroidism / Q000139:chemically induced / Q000201:enzymology* / Q000473:pathology; D007527:Isoenzymes / Q000032:analysis; D008297:Male; D008565:Membrane Proteins / Q000032:analysis*; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology; D009929:Organ Size; D011441:Propylthiouracil / Q000633:toxicity; D021122:Protein Subunits; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000201:enzymology; D014284:Triiodothyronine / Q000008:administration & dosage
D007527:Isoenzymes; D008565:Membrane Proteins; D021122:Protein Subunits; D014284:Triiodothyronine; D011441:Propylthiouracil; D020962:Heterotrimeric GTP-Binding Proteins