Is receptor cross-regulation in human heart caused by alterations in cardiac guanine nucleotide-binding proteins?
1. Guanine nucleotide-binding proteins (G-proteins) play a central role in signal transduction between a wide variety of cell-surface receptors and intracellular second messenger systems. Recently, we and others have demonstrated that cross-regulation can occur between a variety of G-protein-linked receptors in human heart. Chronic beta 1-adrenoceptor blockade gives rise to sensitization of beta 2-adrenoceptor and of 5HT 4-receptor responses, both of which are mediated via stimulation of adenylate cyclase through stimulatory G-proteins (Gs), and also gives rise to desensitization of muscarinic M2-receptor responses, which inhibit adenylate cyclase through inhibitory G-proteins (Gi). 2. In order to investigate whether these effects are due to quantitative changes in cardiac G-protein isoforms, we measured their abundance in right atrial appendage from patients taking or not taking beta 1-adrenoceptor antagonists, by immunoblotting. 3. Samples of right atrial appendage homogenate were subjected to SDS/PAGE, and proteins were electroblotted on to nitrocellulose membranes. These were then probed with specific anti-G protein anti-sera, and binding was revealed by means of a secondary antibody labelled with alkaline phosphatase and using a chromogenic substrate. The resulting bands were quantified by laser densitometry. 4. No quantitative differences were detected, between these two groups of patients, in the amounts of alpha-subunit of 'long' or 'short' Gs isoforms (Gs alpha L and Gs alpha S), or in the amounts of Gi 1 + 2 alpha-subunit (Gi alpha 1 + 2). Nor was any difference found in the abundance of the beta-subunit of G-proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
Ferro
A
A
Clinical Pharmacology Unit, University of Cambridge, Addenbrooke's Hospital, U.K.
Plumpton
C
C
Brown
M J
MJ
D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use; D002318:Cardiovascular Diseases / Q000188:drug therapy / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000032:analysis*; D006801:Humans; D015151:Immunoblotting; D009206:Myocardium / Q000737:chemistry*; D011956:Receptors, Cell Surface / Q000032:analysis*; D015398:Signal Transduction / Q000502:physiology*
D000319:Adrenergic beta-Antagonists; D011956:Receptors, Cell Surface; D019204:GTP-Binding Proteins