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Regulation of G proteins by adenosine receptor agonist in coronary artery
1Department of Pharmacology, School of Medicine, East Carolina University, Greenville, North Carolina 27858.
Insights
Prolonged exposure to 2-chloroadenosine (CAD) alters guanine nucleotide-binding proteins (Gs and Gi) in coronary arteries. This study reveals CAD
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
- G-protein Signaling
Background:
- Prolonged 2-chloroadenosine (CAD) exposure desensitizes coronary artery adenosine receptors.
- The effect of CAD on G-protein subunits (Gs and Gi) in coronary arteries remains unclear.
Purpose of the Study:
- To investigate the impact of CAD on alpha-subunits of stimulatory (Gs) and inhibitory (Gi) guanine nucleotide-binding proteins in coronary arteries.
- To assess the functional consequences of CAD-induced G-protein alterations on muscarinic receptor activation.
Main Methods:
- Coronary arteries were incubated with and without CAD.
- Bacterial toxin-catalyzed ADP ribosylation was used to measure Gs and Gi alpha-subunits.
- Functional response was assessed via muscarinic receptor activation using methacholine.
Main Results:
- CAD treatment time-dependently attenuated cholera and pertussis toxin-catalyzed ADP ribosylation of Gs (45-kDa) and Gi (41-kDa) alpha-subunits.
- CAD induced a concentration-dependent decrease in Gs alpha-subunit ribosylation.
- Pertussis toxin-catalyzed Gi alpha-subunit ribosylation showed a biphasic response to CAD concentration.
- Methacholine-induced contraction was enhanced at low CAD concentrations but unaffected at high concentrations.
Conclusions:
- CAD exposure modulates the alpha-subunits of both Gs and Gi proteins in coronary arteries.
- These alterations in G-protein subunits may underlie functional changes in coronary artery responses to receptor activation.
Abstract:
We have previously reported that prolonged exposure of coronary artery to 2-chloroadenosine (CAD) desensitizes the adenosine receptor without altering the beta-receptor-mediated response (Am. J. Physiol. 264 (Heart Circ. Physiol. 33): H441-H447, 1993). In the present study, alpha-subunits of guanine nucleotide binding proteins, stimulatory (Gs) and inhibitory (Gi), were measured using bacterial toxin-catalyzed ADP ribosylation along with a functional response to Gi protein (through muscarinic receptor activation) in the arteries treated with CAD. Isolated coronary arteries were incubated with and without CAD in culture media. CAD treatment (10(-4) M) resulted in a time-dependent (1, 3, and 7 days) attenuation in the cholera- and pertussis toxin-catalyzed ADP ribosylation of 45- and 41-kDa membrane proteins, respectively. Similarly, the 3-day treatment of the arteries with CAD (10(-8)-10(-4) M) produced a concentration-dependent decrease in cholera toxin-catalyzed ADP ribosylation of 45-kDa protein. Unlike cholera toxin, the alterations in ADP ribosylation of 41-kDa protein catalyzed by pertussis toxin was biphasic, an increase at lower concentration of CAD (10(-8)-10(-6) M) followed by a decrease at higher concentration of CAD (10(-5)-10(-4) M). The contraction-response curve to methacholine, a muscarinic receptor agonist, was significantly shifted to the left in the vascular rings treated with a low concentration of CAD (10(-6) M) while without an effect at high concentration (10(-4) M) of CAD. The data suggest that CAD exposure regulates the alpha-subunits of both Gs and Gi in coronary artery.(ABSTRACT TRUNCATED AT 250 WORDS)