© 2001 by European Society of Cardiology
Copyright © 2000, European Society of Cardiology
Lymphocytes from spontaneously hypertensive rats exhibit enhanced adenylyl cyclase-Gi protein signaling
Department of Physiology, Faculty of Medicine, Groupe de recherche sur le système nerveux autonome, University of Montreal, C.P. 6128, succ. centre-ville, Montreal, Quebec, Canada H3C 3J7
* Corresponding author. Tel.: +1-514-343-2091; fax: +1-514-343-2111 anandsrm{at}physio.umontreal.ca
Objective: We have previously demonstrated an augmented activation of Gi
proteins in heart and aorta from spontaneously hypertensive rats (SHRs), which was attributed to an enhanced expression of Gi proteins. Since immortalized lymphoblasts derived from lymphocytes of hypertensive patients have been shown to have enhanced Gi activation, the present studies were undertaken to investigate if lymphocytes from SHRs also exhibit enhanced Gi activation and whether this activation is related to enhanced expression of Gi proteins. Methods: The levels of G-proteins and mRNA were determined by immunoblotting and Northern blotting techniques, using specific antibodies and cDNA probes, respectively. Adenylyl cyclase activity stimulated or inhibited by agonists was determined to examine the functions of G-proteins. Results: The levels of Gi-2, Gi-3, Gβ but not of Gs45 and Gs47 were significantly increased in lymphocytes from SHRs as compared to their control Wistar Kyoto (WKY) rats. Similarly the mRNA levels of Gi-2 and Gi-3 were significantly augmented in SHRs as compared to their age-matched WKYs. The increased levels of Gi were reflected in increased functions of Gi in SHRs as indicated by increased inhibition of forskolin-stimulated adenylyl cyclase activity by GTP
S. The activity of adenylyl cyclase stimulated by GTPS, isoproterenol, NECA, NaF and forskolin was significantly decreased in SHRs as compared to their age-matched WKY rats. On the other hand, inhibitory hormones, atrial natriuretic peptide and angiotensin II inhibited adenylyl cyclase activity to a greater extent in SHRs as compared to their age-matched WKY rats. Conclusions: These results indicate that lymphocytes from spontaneously hypertensive rats exhibit enhanced Gi activation (function) which may be attributed to the enhanced expression of Gi proteins. It may be suggested that enhanced Gi expression and associated signaling may be one of the factors responsible for enhanced lymphoblasts proliferation observed in hypertension.
KEYWORDS c-ANP4–23, a ring deleted peptide of atrial natriuretic peptide; C-ANP4–23, (des[Gln18,Ser19,Gln20, Leu21,Gly22]ANP4–23-NH2); FSK, forskolin; GTPS, guanosine 5'-[-thio]triphosphate; Gs, stimulatory guanine nucleotide regulatory protein; Gi, inhibitory guanine nucleotide regulatory protein, Go, guanine nucleotide protein of unknown function; NECA, N-ethylcarboxamide adenosine; ISO, isoproterenol, Ang II, angiotensin II