Comparison of the Pharmacological Characteristics of 2-[¹²⁵I]Iodomelatonin Binding Sites in the Lung, Spleen, Brain and Kidney of Chicken

Abstract

We have compared the pharmacological characteristics of 2-[¹²⁵I]iodo-melatonin binding to crude membrane preparations of the lung, spleen, brain and kidney of chicken. Saturation studies indicated significant differences (p < 0.05) in the equilibrium dissociation constant (Kd) and maximum number of binding site (Bmax) values among the four tissues studied. The descending order of affinities was lung = spleen > brain > kidney. Competition curves of 2-[¹²⁵I]iodomelatonin binding to crude membrane preparations of all four chicken tissues by melatonin were studied simultaneously to reduce individual, physiological, age and interassay variations. Similar competition experiments were also performed on 2-phenylmelatonin, 2-iodomelatonin, 6-chloromelatonin, 6-hydroxymelatonin and N-acetylserotonin (NAS). Concentrations of indoles which inhibited 50% of specific 2-[¹²⁵I]iodomelatonin binding (IC₅₀) were calculated. The IC₅₀ of 2-[¹²⁵I]iodomelatonin inhibition curves by the indole compounds in different tissues showed the following descending orders of affinity: (1) melatonin: lung = spleen > brain > kidney, (2) 2-phenylmelatonin: lung = spleen = brain = kidney, (3) 2-iodomelatonin: lung = spleen = kidney > brain, (4) 6-chloromelatonin: lung = spleen = kidney > brain, (5) 6-hydroxymelatonin: kidney > lung = spleen = brain, and (6) NAS: kidney > lung = spleen > brain. The non-hydrolizable GTP analog, guanosine 5''-O-(3-thiotriphosphate) (GTPγS), exhibited differential effects on the saturable binding of the four tissues. GTPγS increased the Kd of 2-[¹²⁵I]iodomelatonin binding by 2- to 3-fold in the lung and spleen, 0.5-fold in the brain and 1-fold in the kidney. Based on our findings, we would like to suggest that the 2-[¹²⁵I]iodomelatonin binding sites in these four tissues may belong to three different high affinity (picomolar) subtypes of melatonin receptor. We name them cML_1Arepresented by the lung and spleen, cML_1B by the brain and cML_1C by the kidney.

2[125I]Iodomelatonin binding and interaction with β‐adrenergic signaling in chick heart/coronary artery physiology

“…The demonstration of picomolar affinity and femtomolar density [ 125 I]Mel binding in the chick heart is consistent with our previous findings that putative melatonin receptors were present in the quail heart [17]. The pharmacological profile was similar to those reported in other avian tissues or cloned melatonin receptors [27,28]. GTPcS modulated the binding affinity indicating that these putative melatonin receptors in the chick heart are coupled to guanine nucleotide-binding proteins (G-proteins).…”

Fixation Stability and Macular Light Sensitivity in Patients with Diabetic Maculopathy: A Microperimetric Study with a Scanning Laser Ophthalmoscope

“…Since the same light source was used for background and stimulus generation, a constant stimulus-to-background ratio was guaranteed [11]. The custom-made software for fundus perimetry [12, 13, 14]allowed for static automatic microperimetry by means of a single crossing staircase strategy similar to conventional perimetry [21, 22, 23]. Light intensity could be varied between 0 and 27.9 dB [dB = 10 × (log maximal intensity/stimulus – background intensity)] where 0 dB represents the brightest luminance (13.2 µW).…”

“…In this study, we performed static automatic microperimetry with the use of a scanning laser ophthalmoscope, which is capable of assessing more aspects of macular function [10, 11, 12]. We developed custom-made software that incorporates two psychophysical measurements commonly performed in the diagnosis and management of macular disease: assessment of localized light sensitivity in the central visual field and determination of fixation stability [12, 13, 14]. …”

Melatonin and Androgen Receptor Expression Interplay Modulates Cell-Mediated Immunity in Tropical Rodent Funambulus pennanti: An In-Vivo and In-Vitro Study

“…In mammals, two distinct G‐protein‐coupled high affinity melatonin receptor subtypes have been identified (mt1, mt2) [6, 7]. Both of these high affinity melatonin receptors have been localized on circulating lymphocytes of rodents, chickens, humans [8, 9] and on thymocytes and splenocytes in humans, several rodents and bird species [10, 11]. In vitro melatonin administration enhances the proliferative ability of splenocytes from both female and male prairie voles (Microtus ochogaster) [12, 13] and in house mice, this enhancement in mice is reported to be attenuated with the addition of the mt2 receptor antagonist, luzindole [14].…”