Islet‐activating protein prevents nicotinic acid‐induced GTPase stimulation and GTP but not GTPγS‐induced adenylate cyclase inhibition in rat adipocytes

Abstract

The influence of islet-activating protein (IAP), a Bordetella pertussis toxin, was studied on adenylate cyclase and GTPase activities in rat adipocyte membranes. Pretreatment of rats or intact rat adipocytes with IAP did not affect adenylate cyclase inhibition by the stable GTP analog, GTP$$ whereas inhibition by GTP was abolished. Concomitantly, activation of the adipocyte enzyme by sodium and its inhibition by nicotinic acid were prevented. Furthermore, IAP treatment of adipocyte membranes prevented nicotinic acid-induced stimulation of a high affinity GTPase. The data suggest that a GTP-hydrolyzing system involved in the inhibitory regulation of adenylate cyclase is the target of IAP's action.

Characterization of a G Protein-Coupled Receptor for Nicotinic Acid

“…In agreement with a previous report (Aktories et al, 1983), we have found that G protein activation by nicotinic acid in adipocyte membranes is sensitive to pertussis toxin. However, [ 3 H]nicotinic acid to spleen membranes was inhibited by the toxin only to a minor extent.…”

“…It has been reported previously that GTPase activation and adenylyl cyclase inhibition by nicotinic acid in adipocyte membranes are pertussis toxin-sensitive (Aktories et al, 1983). In agreement with these findings, we found that pertussis toxin pretreatment of rat adipocyte membranes reduced stimulation of […”

“…Nicotinic acid and related heterocyclic agents activate pertussis toxin-sensitive GTPase and inhibit adenylyl cyclase in a hormone-like manner (Aktories et al, 1980a(Aktories et al, ,b, 1982(Aktories et al, , 1983. A specific receptor has been proposed (Aktories et al, 1980a), but no direct evidence for its existence has been presented so far.…”

“…This action of nicotinic acid and analogs involves a decrease in cellular cyclic AMP levels by inhibition of adipocyte adenylyl cyclase (Aktories et al, 1980a) and stimulation of a high-affinity GTPase in fat cell membranes (Aktories et al, 1980b(Aktories et al, , 1982. The inhibition of adenylyl cyclase requires a functional G protein of the G i /G o family because GTPase activation as well as adenylyl cyclase inhibition are prevented by pertussis toxin (Aktories et al, 1983). In contrast, augmentation of insulin-stimulated glucose transport by nicotinic acid in rat adipocytes requires a pertussis toxin-sensitive G protein, but is probably independent from cyclic AMP (Kuroda et al, 1987;Honnor et al, 1992).…”

Guanine‐nucleotide‐dependent inhibition of adenylate cyclase of rabbit heart by glucagon

“…KCI, which extracts peripheral proteins, could conceivably further decrease the number of membranebound N proteins. Due to possible changes in the stoichiometric ratio between N and receptor molecules, similar hormonal responses may require activation of more receptors and, ( I mglml) were preincubated in the absence or presence of 1 pg/ml of trypsin (Sigma) at 33 ~ C. The incubation medium contained 25 mM Tris/HCI, pH 7.6 and 0.05 2, bovine serum albumin. After 5 min, soybean trypsin inhibitor (Sigma) was added to both the trypsin-treated and control membranes at a final concentration of 10pg/ml and 4O-pl therefore, higher hormone concentrations in isolated membranes compared to intact cells.…”