The incorporation of cholesterol into human platelets by means of incubation with cholesterol-rich lecithin dispersions is associated with a decreased fluidity in the phospholipid hydrocarbon core of platelet membranes and an increased sensitivity of platelets to aggregating agents. We examined whether the platelet membrane enzyme, adenylate cyclase is influenced by changes in phospholipid flui...

The cultured murine Leydig tumor cell line MLTC-1 and the normal rat thyroid strain FRTL have adenylate cyclase activities that are stimulated by human chorionic gonadotropin (hCG) and thyrotropin, respectively. Both cell types also respond to choleragen. Activation of adenylate cyclase in membranes by choleragen required NAD whereas stimulation of the enzyme by hormones did not. With [alpha-32...

Acute and persistent rabies virus infection of mouse neuroblastoma-rat glioma hybrid cells (NG-108-15) results in a loss of the normal inhibiting function of opiates via the opiate receptor on hormone-stimulated adenylate cyclase activity. Previous studies of these persistently infected cells have shown a decrease in the affinity of the opiate receptors for agonists without any change in the nu...

Changes in the beta-adrenergic receptor-G protein-adenylate cyclase complex were investigated in an experimental canine model of low-output heart failure produced by chronic rapid ventricular pacing. The contractile response occurring after exposure to the beta-adrenergic agonist dobutamine, measured as peak left ventricular + dP/dt, was decreased after 3 weeks of pacing. To further characteriz...

The action of thyrotropin (TSH) on plasma membranes was studied to elucidate the mechanism of hormonal regulation of malignant versus normal human thyroid tissue. Thyroid plasma membranes of six specimens of papillary or follicular carcinoma and six of adenoma, as well as adjacent normal tissue obtained from these patients, were evaluated with respect to binding of 125I-labeled TSH and stimulat...

Activity of adenylate cyclase [(EC 4.6.1.1) ATP pyrophosphate lyase (cyclizing)] in purified rat ovarian plasma membranes undergoes partial desensitization (30-60%) upon exposure to saturating lutropin (LH, 0.1 p ~ ) and GTP (1 p ~ ) . Decline in hormone responsiveness of the enzyme is dose-dependent with regard to LH ( K , = 1.7 IWI +. 1) and GTP ( K , = 0.19 p~ f 0.02), indicating that the ac...

For a variety of ligand states, adenylate cyclase activity in the presence of Mn2+ was greater than with Mg2+. Trypsin treatment of intact hepatocytes, under conditions which destroy cell surface glucagon receptors, led to a first order loss of glucagon-stimulated adenylate cyclase activity in isolated membranes assayed in the presence of Mn2+ whether or not GTP (100 microM) was present in the ...

Opiates and opioid peptides inhibit adenylate cyclase and stimulate specific low Km GTPase activity in membranes from neuroblastoma x glioma NG108-15 hybrid cells. The effects of opiate agonists on both enzymes are mediated by high affinity stereospecific receptors and require Mg2+, GTP, and Na+. In the presence of Mg2+, Na+ inhibits basal GTPase activity; opiates stimulate GTP hydrolysis by an...

Bradykinin and phorbol 12-myristate 13-acetate stimulate adenylate cyclase activity in serum-depleted cultured airway smooth muscle via a protein kinase C (PKC)-dependent pathway. The probable target is the type II adenylate cyclase, which can integrate coincident signals from both PKC and Gs. Therefore, activation of Gs (by cholera-toxin pre-treatment) amplified the bradykinin-stimulated cycli...

Human platelet membranes contain a2 adrenergic receptors which mediate the guanine nucleotide-dependent inhibition of adenylate cyclase induced by epinephrine. Previous investigations have provided insight into the mechanisms of adenylate cyclase stimulation by studying hormone-induced release of radiolabeled guanine nucleotides from membranes preincubated with the nucleotides. In the present s...