Effect of asymmetry of concentration–response curves on the results obtained by the receptorial responsiveness method (RRM): an in silico study

Abstract

The receptorial responsiveness method (RRM) was proposed to estimate changes in the concentration of an agonist in the microenvironment of its receptor. Usually, this is done by providing the equieffective concentration of another agonist for the same receptor or for a largely overlapping postreceptorial signaling ("test agonist"). The RRM is a special nonlinear regression algorithm to analyze a concentration-response (E/c) curve that represents the simultaneous actions of a single agonist concentration to be estimated and of increasing concentrations of the test agonist. The aim of this study was to explore whether asymmetry of the E/c curve to be analyzed influences the reliability of the RRM. For this purpose, computer simulation was performed by constructing symmetric and asymmetric E/c curves using the operational model of agonism, and then these curves were analyzed with the RRM. To perform the RRM, 2 types of equations were used: one involving the Hill equation, the simplest model of the E/c relationship, and one containing the Richards equation, an advanced model properly handling E/c curve asymmetry. Results of this study indicate that E/c curve asymmetry does not significantly influence the accuracy of the estimates provided by the RRM. Thus, when using the RRM, it is not necessary to replace the Hill equation with the Richards equation to obtain useful estimates. Furthermore, it was found that estimation of a high concentration of a high-efficacy agonist can fail when the RRM is performed with a low-efficacy test agonist in a system characterized by a small operational slope factor.

Accuracy and Precision of the Receptorial Responsiveness Method (RRM) in the Quantification of A1 Adenosine Receptor Agonists

“…It should be noted that the traditional methods to determine receptor reserve have not proved to be useful for adenosine due to the short half-life of adenosine [33], although receptor reserve values in the cardiac adenosinergic system seem to be of importance, even in terms of diagnostic aspects [34]. Finally, of course, data that were obtained with RRM can serve as input data for in silico investigations dealing with the RRM itself [14,15], and with the adenosinergic mechanisms in the atrial myocardium [35,36].…”

“…One of these concentrations is indicated by the x-axis, while the other one, c x , is a concentration of the agonist used for the E/c curve that is equieffective with the agonist added in a single extra dose. If the two agonists in question are the same, c x is a real concentration, and, if not, c x is a surrogate parameter of the single extra concentration of the other agonist [14,15]. The application of RRM might be useful when the concentration of this extra agonist is unknown and difficult to determine in any other manners [12,13].…”

The guinea pig atrial A1 adenosine receptor reserve for the direct negative inotropic effect of adenosine

“…The biased adenosine E/c curves were not suitable for the assessment of A 1 adenosine receptor reserve, the goal of the present study. Therefore, effects of adenosine E/c curves biased by NBTI were corrected by means of RRM, our method validated for quantifying changes in agonist concentrations in the microenvironment of the receptors (Gesztelyi et al 2004;Grenczer et al 2010aGrenczer et al , 2010b.…”

“…Because NBTI strongly affects the fate of exogenous adenosine used to generate an E/c curve (Szentmiklosi et al 1982;Gesztelyi et al 2003a), adenosine could not be used as an agonist for the E/c curves essential for RRM (Karsai et al 2006). However, RRM enables replacement of a degradable agonist with a stable one (Gesztelyi et al 2004;Grenczer et al 2010aGrenczer et al , 2010b. Thus, the surplus interstitial adenosine accumulated by NBTI was quantified using E/c curves generated with CPA, an A 1 receptor agonist with a significantly longer half-life in living tissues than adenosine (see Eq.…”

Attenuated Vasodilator Effectiveness of Protease-Activated Receptor 2 Agonist in Heterozygous par2 Knockout Mice

“…While the concept of spare receptors aligns with our observations and offers one explanation for the closer resemblance of PAR2-HET to PAR2-WT than to PAR2-KO, it does exclude other possible mechanisms. It is known that receptor number does not always correlate with biological responsiveness [22]. One could argue that PAR2-HET have less PAR2 expression than PAR2-WT and compensatory downstream mechanisms sustain the capacity to elicit a near maximal cellular response.…”