guanosine-5--o-(3-thiotriphosphate) and Cat-Diseases

To evaluate alterations in ligand-stimulated activity of G proteins in thyroid gland cells of hyperthyroid cats.. Membranes of thyroid gland cells isolated from 5 hyperthyroid cats and 3 age-matched euthyroid (control) cats immediately after the cats were euthanatized.. Isolated thyroid cell membranes were treated with thyroid-stimulating hormone (TSH), and activation of G protein was quantified by measurement of the binding of guanosine triphosphate gamma labeled with sulfur 35 (GTPgamma(35)S). The separate effects of G-protein inhibitory (G(i)) and G-protein stimulatory (G(s)) proteins were determined by the use of pertussis toxin and cholera toxin, respectively.. Thyroid cell membranes from hyperthyroid cats had higher basal GTPgamma(35)S binding than did thyroid cell membranes from euthyroid cats. Thyroid cell membranes from hyperthyroid and euthyroid cats had a concentration-dependent increase in TSH-stimulated GTPgamma(35)S binding over the TSH range of 0 to 100 mU/mL, with maximal activity at 1 to 100 mU/mL for both. The percentage increase in GTPgamma(35)S binding stimulated by TSH was similar in magnitude between the membranes from hyperthyroid and euthyroid cats. The TSH-stimulated activation of G(s) and G(i) was not different between euthyroid and hyperthyroid cats.. Ligand-stimulated activation of G proteins was the same in thyroid cell membranes obtained from hyperthyroid and euthyroid cats. Therefore, alterations in inherent G(s) or G(i) activities did not appear to be part of the pathogenesis of hyperthyroidism in cats.

Topics: Animals; Cat Diseases; Cats; Cholera Toxin; Female; GTP-Binding Protein alpha Subunits, Gi-Go; GTP-Binding Protein alpha Subunits, Gs; Guanosine 5'-O-(3-Thiotriphosphate); Hyperthyroidism; Linear Models; Male; Pertussis Toxin; Thyrotropin

Phosphoinositide-specific phospholipase C and adenylyl cyclase were studied in brain cortical membranes from cats with GM1 and GM2 gangliosidosis. In contrast to brain cortical membranes from unaffected control cats, phospholipase C acting against exogenously supplied phosphoinositide substrates did not respond to stimulation by GTP gamma S, carbachol or fluoroaluminate in cortical membranes of cats with gangliosidosis. However, the enzyme was activated by calcium in membranes from affected cats to the same extent as in membranes from control cats. Basal adenylyl cyclase activity was increased 3-fold in cortical membranes of cats with GM1 and GM2 gangliosidosis, compared with unaffected sibling controls. Fluoroaluminate was equally effective in stimulating adenylyl cyclase in controls and in membranes of affected and normal cats. In addition, GppNHp was able to inhibit the forskolin-activated enzyme both in membranes from cats with gangliosidosis and sibling controls. These data suggest that the activation of phosphoinositide-specific phospholipase C in brain membranes by guanine nucleotide binding proteins is markedly impaired in GM1 and GM2 gangliosidoses.

Topics: Adenylyl Cyclases; Aluminum; Aluminum Chloride; Aluminum Compounds; Animals; Calcium; Carbachol; Cat Diseases; Cats; Cell Membrane; Cerebral Cortex; Chlorides; Colforsin; G(M1) Ganglioside; Gangliosidoses; Gangliosidosis, GM1; Guanosine 5'-O-(3-Thiotriphosphate); Guanylyl Imidodiphosphate; Kinetics; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositol Diacylglycerol-Lyase; Phosphatidylinositols; Phosphoric Diester Hydrolases; Reference Values; Sodium Fluoride