%0 Journal Article %1 Klotz1990 %A Klotz, K. N. %A Keil, R. %A Zimmer, F. J. %A Schwabe, U. %D 1990 %J J Neurochem %K Animals Brain/*metabolism Centrifugation Ethylmaleimide/pharmacology Factors Guanosine Kinetics Membranes/metabolism Purinergic/*metabolism Rats Solubility Time Triphosphate/*pharmacology Xanthines/*metabolism Receptor %N 6 %P 1988-94 %T Guanine nucleotide effects on 8-cyclopentyl-1,3-3Hdipropylxanthine binding to membrane-bound and solubilized A1 adenosine receptors of rat brain %U http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2338552 %V 54 %X The effects of guanine nucleotides on binding of 8-cyclopentyl-1,3-3Hdipropylxanthine (3HDPCPX), a highly selective A1 adenosine receptor antagonist, have been investigated in rat brain membranes and solubilized A1 receptors. GTP, which induces uncoupling of receptors from guanine nucleotide binding proteins, increased binding of 3HDPCPX in a concentration-dependent manner. The rank order of potency for different guanine nucleotides for increasing 3HDPCPX binding was the same as for guanine nucleotide-induced inhibition of agonist binding. Therefore, a role for a guanine nucleotide binding protein, e.g., Gi, in the regulation of antagonist binding is suggested. This was confirmed by inactivation of Gi by N-ethylmaleimide (NEM) treatment of membranes, which resulted in an increase in 3HDPCPX binding similar to that seen with addition of GTP. Kinetic and equilibrium binding studies showed that the GTP- or NEM-induced increase in antagonist binding was not caused by an affinity change of A1 receptors for 3HDPCPX but by an increased Bmax value. Guanine nucleotides had similar effects on membrane-bound and solubilized receptors, with the effects in the solubilized system being more pronounced. In the absence of GTP, when most receptors are in a high-affinity state for agonists, only a few receptors are labeled by 3HDPCPX. It is suggested that 3HDPCPX binding is inhibited when receptors are coupled to Gi. Therefore, uncoupling of A1 receptors from Gi by guanine nucleotides or by inactivation of Gi with NEM results in an increased antagonist binding.

@article{Klotz1990, abstract = {The effects of guanine nucleotides on binding of 8-cyclopentyl-1,3-[3H]dipropylxanthine ([3H]DPCPX), a highly selective A1 adenosine receptor antagonist, have been investigated in rat brain membranes and solubilized A1 receptors. GTP, which induces uncoupling of receptors from guanine nucleotide binding proteins, increased binding of [3H]DPCPX in a concentration-dependent manner. The rank order of potency for different guanine nucleotides for increasing [3H]DPCPX binding was the same as for guanine nucleotide-induced inhibition of agonist binding. Therefore, a role for a guanine nucleotide binding protein, e.g., Gi, in the regulation of antagonist binding is suggested. This was confirmed by inactivation of Gi by N-ethylmaleimide (NEM) treatment of membranes, which resulted in an increase in [3H]DPCPX binding similar to that seen with addition of GTP. Kinetic and equilibrium binding studies showed that the GTP- or NEM-induced increase in antagonist binding was not caused by an affinity change of A1 receptors for [3H]DPCPX but by an increased Bmax value. Guanine nucleotides had similar effects on membrane-bound and solubilized receptors, with the effects in the solubilized system being more pronounced. In the absence of GTP, when most receptors are in a high-affinity state for agonists, only a few receptors are labeled by [3H]DPCPX. It is suggested that [3H]DPCPX binding is inhibited when receptors are coupled to Gi. Therefore, uncoupling of A1 receptors from Gi by guanine nucleotides or by inactivation of Gi with NEM results in an increased antagonist binding.}, added-at = {2010-12-14T18:12:02.000+0100}, author = {Klotz, K. N. and Keil, R. and Zimmer, F. J. and Schwabe, U.}, biburl = {https://www.bibsonomy.org/bibtex/21d6694fa0effd1c09e207069b5aeff68/pharmawuerz}, endnotereftype = {Journal Article}, interhash = {3d06c90447e388ffe7c526f896b3429c}, intrahash = {1d6694fa0effd1c09e207069b5aeff68}, issn = {0022-3042 (Print) 0022-3042 (Linking)}, journal = {J Neurochem}, keywords = {Animals Brain/*metabolism Centrifugation Ethylmaleimide/pharmacology Factors Guanosine Kinetics Membranes/metabolism Purinergic/*metabolism Rats Solubility Time Triphosphate/*pharmacology Xanthines/*metabolism Receptor}, month = Jun, note = {Klotz, K N Keil, R Zimmer, F J Schwabe, U Research Support, Non-U.S. Gov't United states Journal of neurochemistry J Neurochem. 1990 Jun;54(6):1988-94.}, number = 6, pages = {1988-94}, shorttitle = {Guanine nucleotide effects on 8-cyclopentyl-1,3-[3H]dipropylxanthine binding to membrane-bound and solubilized A1 adenosine receptors of rat brain}, timestamp = {2010-12-14T18:20:05.000+0100}, title = {Guanine nucleotide effects on 8-cyclopentyl-1,3-[3H]dipropylxanthine binding to membrane-bound and solubilized A1 adenosine receptors of rat brain}, url = {http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2338552}, volume = 54, year = 1990 }