[¹²⁵l]lodomelatonin Binding Sites in Mammalian and Avian Kidneys

Abstract

[^I25I]Iodomelatonin binding sites have been identified and characterized in kidneys of birds and mammals. These binding sites in the kidneys of guinea pig, duck and chicken were found to be stable, reversible, saturable, specific and of high affinity. The binding densities (B_max) of [¹²⁵I]iodomelatonin binding sites in the kidneys of guinea pig, duck and chicken ranged from 1.07 to 6.43 fmol/mg protein and the equilibrium dissociation constants (K_d) from 19.2 to 44.6 pmol/l at the middle of the light period (mid-light). It appears that [¹²⁵I]iodomelatonin binding in the kidneys of mammalian species may have lower densities compared with birds. In the mammals studied, the guinea pig kidney showed the highest [¹²⁵I]iodomelatonin binding. Pharmacological data indicated that the [¹²⁵I]iodomelatonin binding to kidneys of guinea pig, duck and chicken was highly specific to melatonin, 2-iodomelponin and 6-chloromelatonin. Diurnal variations in the B_max of [¹²⁵I]iodomelatonin binding sites were detected in the kidneys of duck and chicken with no difference in affinity. However, there was no diurnal variation in the K_d or B_max in the guinea pig kidneys. The density of [¹²⁵I]iodomelatonin binding sites in the cortex of guinea pig kidney was more than 8-fold higher than the binding in the medulla. Guanosine 5''-O-(3-thiotriphosphate) (GTPγS; 10 µmol/1) reduced the B_max and increased the K_d of [¹²⁵I]iodomelatonin binding sites in the chicken kidney. However, in the membrane preparations of the guinea pig kidney, co-incubation with GTPγS (15 µmol/l) increased the K_d with no effect on the B_max of the [¹²⁵I]iodomelatonin binding. The effects of GTPγS on the kidney [¹²⁵I]iodomelatonin binding suggest that these binding sites may couple to a G protein. The identification of [¹²⁵I]iodomelatonin binding sites in the kidneys of mammals and birds supports the possibility of melatonin acting directly on the renal system.

Molecular and functional characterization of a partial cDNA encoding a novel chicken brain melatonin receptor

“…In contrast, the chicken lung revealed trace amounts of MLR mRNA. The mRNA distribution patterns of the cloned cMLR are in line with the known distribution patterns of native receptors in avian brain and peripheral tissues, as determined by both ligand-binding and receptor autoradiography [23,26,27,44]. In situ hybridization analysis will be necessary to clearly define the tissue-specific and cellular distribution profile of MLR mRNAs in this species.…”

“…In the retina, ML inhibits dopamine synthesis and release [24] with a pharmacological profile and rank order of potency corresponding to the high-affinity ML~ receptor [25] found in either the rabbit retina or other neuronal and peripheral tissues from the same or different species ( [26,27] and see [2,13]). Moreover, in the retina, many opposing physiological and regulatory actions between dopamine and ML have been documented (see [28] and references therein).…”

2-[¹²⁵I]Iodomelatonin Binding Sites in the Testis and Ovary: Putative Melatonin Receptors in the Gonads

“…Saturation experiments with crude salmon brain membranes also showed no significant differences in 2-[l25I]iodomelalonin binding related to the time of day but autoradiographic studies of the same tissues indicated a higher 2-[I25I]iodomelatonin binding during the dark period in the preoptic area [78], Inversely related to serum melaton in concentrations, higher 2-[l25I]iodomelatonin binding density during midlight with no change in the apparent Kd values was re ported in quail [79], pigeon [80] and chicken brain [81,82], chicken, pigeon and duck kid ney [50,83], chicken, pigeon and quail bursa of Fabricius [84,85] and duck thymus [86], In mammals, similar diurnal variations were found in the rat brain [87,88], rat anterior pituitary and pars tuberalis [89] with a de crease in 2-[l25I]iodomelatonin binding densi ty at the beginning of the dark phase and no variation in the affinity of 2-[125I]iodomelatonin binding throughout the 24-hour cycle. Quantitative autoradiography also demon strated maximum 2-[125I]iodomelatonin binding density at the light-dark transition in rat suprachiasmatic nuclei and pars tuberalis [90,91],…”

Biological Basis and Possible Physiological Implications of Melatonin Receptor- Mediated Signaling in the Rat Epididymis

“…Despite the growing recognition of a direct action of melatonin on peripheral tissues [32,[41][42][43][44][45] including the blood vessel [46][47][48][49], spleen [50][51][52], bursa of Fabricius [53], thymus [54], immune cells [55,56], gut [57][58][59][60][61][62], heart [63,64], lung [63,65], kidney [66][67][68], salt gland [69], adrenal [70][71][72], liver [73] and reproductive tissues [18][19][20][21][22][23][24][25][26][27][28][29][30][31], many of the molecular and cellular mechanisms of melatonin signaling on these target tissues remain undefined. In the past few years, our labora...…”