Positive coupling of beta-like adrenergic receptors with adenylate cyclase in the cnidarian Renilla koellikeri

Coupling of the previously characterized beta1- and beta2-like adrenoceptors in the sea pansy Renilla koellikeri with adenylate cyclase was examined in membrane preparations from this cnidarian. Adenylate cyclase activity was stimulated by several guanine nucleotides, such as GTP, Gpp(NH)p and GTPgammaS. Fluoride ions and cholera toxin greatly enhanced the enzyme activity, whereas forskolin had no effect on basal or isoproterenol-induced stimulation of the enzyme. The stimulation of adenylate cyclase activity by several beta-adrenergic agonists in different parts of the animal reflected a positive coupling with the beta2- and beta1-like adrenoceptors in autozooid and peduncle tissues, respectively. In addition, isoproterenol-induced stimulation of adenylate cyclase activity was dependent on guanine nucleotides, suggesting coupling mediated by a G protein. The pharmacological profile of various antagonists on isoproterenol-sensitive adenylate cyclase in autozooid and peduncle tissues matched that of previous radioligand binding studies. Isoproterenol-induced stimulation of adenylate cyclase activity in rachidial tissues was partially inhibited by trifluoperazine of (+/−)CGP12177 and was completely blocked in the presence of both antagonists. This suggests that coupling of the enzyme occurs with beta1- and beta2-like adrenoceptors, both being present in the rachis. Serotonin and dopamine were also found to stimulate adenylate cyclase activity. Their stimulatory effect was additive to isoproterenol-induced activation, suggesting the presence of dopaminergic and serotonergic receptors in the tissues of the sea pansy. Along with the data presented previously on beta-adrenergic binding, this study suggests that elements of receptor-dependent G protein signal transduction originated early in invertebrate evolution.

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Stimulation of mammalian adenylate cyclase activity with guanosine 5′-tetraphosphate and other guanine nucleotides

Biochimica et Biophysica Acta (BBA) - General Subjects ◽

10.1016/0304-4165(78)90390-2 ◽

1978 ◽

Vol 541 (2) ◽

pp. 170-180 ◽

Cited By ~ 2

Author(s):

Louis J. Ignarro ◽

Rosemarie A. Gross

Keyword(s):

Adenylate Cyclase ◽

Guanine Nucleotides ◽

Cyclase Activity ◽

Adenylate Cyclase Activity ◽

Stimulation Of

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Regulation of PTH receptor-adenylate cyclase system of canine kidney: influence of Mn2+ on effects of Ca2+, PTH, and GTP

AJP Renal Physiology ◽

10.1152/ajprenal.1982.242.5.f457 ◽

1982 ◽

Vol 242 (5) ◽

pp. F457-F462

Author(s):

E. Bellorin-Font ◽

J. Tamayo ◽

K. J. Martin

Keyword(s):

Enzyme Activity ◽

Adenylate Cyclase ◽

Metal Ions ◽

Guanine Nucleotides ◽

Cyclase Activity ◽

Adenylate Cyclase Activity ◽

Adenylate Cyclase System ◽

Guanine Nucleotide ◽

Hormone Binding ◽

Stimulation Of

Metal ions play important roles in the regulation of the activation of adenylate cyclase. Previous studies have suggested that an important site of action of metal ions is at or closely related to the nucleotide regulatory protein. The present studies examine the nature of the regulation of enzyme activity by divalent cations and the influence of Mn2+ on hormone binding and stimulation of adenylate cyclase. Studies were performed in canine renal cortical membranes. Substitution of Mg2+ by Mn2+ was associated with a progressive decline in the ability of GTP or PTH to stimulate adenylate cyclase activity. Mn2+ did not alter specific binding of an iodinated PTH analogue. However, in spite of the loss of guanine nucleotide stimulation of enzyme activity, the effects of guanine nucleotide on PTH binding were not altered in the presence of Mn2+. Substitution of Mg2+ by Mn2+ abolished the inhibitory effect of Ca2+ on basal adenylate cyclase activity. Similarly, the effects of GTP or PTH to enhance the inhibitory effects of Ca2+ on enzyme activity were abolished in the presence of Mn2+. Since Mg2+ and Ca2+ compete for a common allosteric site and Mn2+ abolished the effects of these cations, it would appear that Mn2+ also competes for the binding site of Mg2+ and Ca2+. The present studies demonstrating that Mn2+ does not affect hormone binding or the actions of guanine nucleotides on hormone binding yet totally eliminates the effect of GTP on enzyme activity indicate that the effect of Mn2+ occurs at the level of the interactions of the nucleotide regulatory component with the catalytic unit. In addition, these data suggest that there are two functionally distinct sites of guanine nucleotides with different ionic requirements.

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Regulation of adenylate cyclase and cyclic AMP phosphodiesterase by 5-hydroxytryptamine and calcium ions in blowfly salivary-gland homogenates

Biochemical Journal ◽

10.1042/bj2040153 ◽

1982 ◽

Vol 204 (1) ◽

pp. 153-159 ◽

Cited By ~ 16

Author(s):

I Litosch ◽

M Fradin ◽

M Kasaian ◽

H S Lee ◽

J N Fain

Keyword(s):

Salivary Gland ◽

Cyclic Amp ◽

Adenylate Cyclase ◽

Guanine Nucleotides ◽

Cyclase Activity ◽

Adenylate Cyclase Activity ◽

Cyclic Amp Phosphodiesterase ◽

Maximal Stimulation ◽

Increased Activity ◽

Stimulation Of

Salivary-gland homogenates contain 5-hydroxytryptamine-stimulated adenylate cyclase. Half-maximal stimulation was obtained with 0.1 microM-5-hydroxytryptamine in the presence of added guanine nucleotides. Gramine antagonized the stimulation of cyclase caused by 5-hydroxytryptamine. In the presence of hormone, guanosine 5′-[gamma-thio]triphosphate produced a marked activation of adenylate cyclase activity. Stimulation of adenylate cyclase by forskolin or fluoride did not require the addition of guanine nucleotides or hormone. In the presence of EGTA, Ca2+ produced a biphasic activation of cyclase activity. Ca2+ at 1-100 microM increased activity, whereas 2000 microM-Ca2+ inhibited cyclase activity. The neuroleptic drugs trifluoperazine and chlorpromazine non-specifically inhibited adenylate cyclase activity even in the absence of Ca2+. The cyclic AMP phosphodiesterase activity in homogenates was not affected by Ca2+ or exogenous calmodulin. This enzyme was also inhibited by trifluoperazine in the absence of Ca2+. These results indicate that Ca2+ elevates adenylate cyclase activity, but had no effect on cyclic AMP phosphodiesterase of salivary-gland homogenates.

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