Biomedical subjects

D S Darling

Publications and source records attributed to D S Darling.

38 records · Page 3Linked to original sources

PubMed1987

Nuclear receptors for L-triiodothyronine in trout erythrocytes.

We have developed an in vitro assay to evaluate saturable specific binding of triiodothyronine (T3) by erythrocyte (RBC) nuclei isolated from rainbow trout. Our results indicate that the nuclei contain a T3-saturable protein which binds T3 with temperature, and pH dependency, high T3 affinity (Ka = 1.6 X 10(9) M-1), and relative thyroid hormone (TH) analog affinities (TRIAC greater than T3 greater than T4 greater than rT3 greater than T2) which are characteristic of TH receptors in other vertebrates. Our estimate of the maximal T3 binding capacity (MBC) of nuclei isolated from heterogeneous populations of RBCs at different maturational stages (MBC = 3.6 fM/mg DNA; 13 sites/nucleus) was 10-100 times lower than would be expected of a TH-responsive tissue. Differential cell counts revealed that 1% of the RBCs in our trout were immature (pro-RBCs). Pro-RBCs, in contrast to mature RBCs, contain abundant heterochromatin, mitochondria, and polyribosomes, and synthesize hemoglobin. Evaluation of binding data for RBC nuclei taken from trout in which erythropoiesis was stimulated by prior bleeding indicated that MBC was directly proportional to the absolute number of pro-RBC nuclei in the incubation. Our maximum estimate of MBC for pro-RBC nuclei (458 fmol/mg DNA; 1781 sites/nucleus) falls within the range of MBC values reported for other vertebrate TH-responsive tissues. These data indicate that RBCs of rainbow trout contain a nuclear protein (putative receptor) which binds T3 with characteristics similar to the TH receptor of higher vertebrates, and that nuclear T3 binding may be diminished during RBC maturation.

Animals↗

PubMed1982

Comparison of thyroid hormone binding to heptic nuclei of the rat and a teleost (Oncorhynchus kisutch).

A modified T3 binding assay was used with coho salmon liver nuclei. Purified nuclei were incubated with [125I]T3 (or [125I]T4), nonradioactive thyroid hormone, or thyroid hormone analog. Bound hormone was separated from hormone by use of polyethylene glycol. Salmon liver nuclei specifically bound T3 with a high affinity [Ka = 1.031 +/- 0.174 x 10(9) M-1 (mean +/- SE); n = 12] which was 50% of the affinity measured with rat liver nuclei using the same assay. Salmon nuclear T3-binding capacity was 0.127 +/- 0.035 pmol T3/mg DNA (n = 7). Rat liver nuclear capacity for T3 binding was 3.4-fold greater than in salmon liver nuclei. T3 binding to salmon liver nuclei was greater than to nuclei from salmon brain; T3 binding to salmon spleen nuclei was low. Binding competition studies with hormone analogs indicated that binding to the salmon nuclei was dependent on molecular structure. These data indicate that the T3 binding to salmon nuclei may be due to T3 receptor activity. Analysis of Scatchard plots showed that the affinity of salmon hepatic nuclei for T3 is 10-fold greater than the affinity for T4. Reciprocal binding competition experiments with T3 and T4 indicate that both hormones bind to the same site. This suggests that in salmon, as in mammals, the liver nuclei predominantly bind thyroid hormones at T3-binding sites. Hepatic nuclei of human, rat, chick embryo, amphibian larva, and salmon have similar affinities for thyroid hormones and similar relative affinities for several thyroid hormone analogs, suggesting that the receptor molecule has been highly conserved during evolution.

Animals↗