title: Calcium and calmodulin in the regulation of human thyroid adenylate cyclase activity.
abstract: TSH (thyrotropin)-stimulated human thyroid adenylate cyclase has a biphasic response to Ca2+, being activated by submicromolar Ca2+ (optimum 22nM), with inhibition at higher concentrations. Calmodulin antagonists caused an inhibition of TSH-stimulated adenylate cyclase in a dose-dependent manner. Inhibition of TSH-and TSIg-(thyroid-stimulating immunoglobulins)-stimulated activity was more marked than that of basal, NaF- or forskolin-stimulated activity. This inhibition was not due to a decreased binding of TSH to its receptor. Addition of pure calmodulin to particulate preparations of human non-toxic goitre which had not been calmodulin-depleted had no effect on adenylate cyclase activity. EGTA was ineffective in removing calmodulin from particulate preparations, but treatment with the tervalent metal ion La3+ resulted in a loss of up to 98% of calmodulin activity from these preparations. Addition of La3+ directly to the adenylate cyclase assay resulted in a partial inhibition of TSH- and NaF-stimulated activity, with 50% inhibition produced by 5.1 microM and 4.0 microM-La3+ respectively. Particulate preparations with La3+ showed a decrease of TSH- and NaF-stimulated adenylate cyclase activity (approx. 40-60%). In La3+-treated preparations there was a decrease in sensitivity of TSH-stimulated adenylate cyclase to Ca2+ over a wide range of Ca2+ concentrations, but most markedly in the region of the optimal stimulatory Ca2+ concentration. In particulate preparations from which endogenous calmodulin had been removed by La3+ treatment, the addition of pure calmodulin caused an increase (73 +/- 22%; mean +/- S.E.M., n = 8) in TSH-stimulated thyroid adenylate cyclase activity. This was seen in 8 out of 13 experiments.
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007811:Lanthanum / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D013961:Thyroid Gland / Q000187:drug effects / Q000201:enzymology*; D013972:Thyrotropin / Q000494:pharmacology
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D002147:Calmodulin; D010726:Phosphodiesterase Inhibitors; D013449:Sulfonamides; C017967:W 7; D007811:Lanthanum; D013972:Thyrotropin; D000262:Adenylyl Cyclases; D002118:Calcium