Separate binding sites for intact PTH 1-84 and synthetic PTH 1-34 in canine kidney |
| |
Authors: | Juan C Garcia Charles L McConkey Kevin J Martin MD |
| |
Institution: | (1) Renal Division, Department of Internal Medicine, Washington University School of Medicine, 660 South Euclid Ave, Box 8126, 63110 St. Louis, Missouri, USA |
| |
Abstract: | Summary The present studies examine the characteristics of parathyroid hormone (PTH) receptor binding in canine basolateral renal
cortical membranes using iodinated preparations of intact bovine PTH 1-84 and Nle8, Nle18, Tyr34] bPTH 1-34 amide. A solid phase lactoperoxidase technique was used to iodinate the bPTH 1-84. The PTH 1-34 analog was iodinated
using chloramine T. Both radioligands were purified by reverse phase high pressure liquid chromatography (HPLC). Specific
binding of125I PTH 1-84 reached equilibrium at 3 hours whereas binding of the125I PTH 1-84 analog reached equilibrium at 45 minutes. Excess bPTH 1-84 resulted in complete inhibition of binding of125I bPTH 1-84, whereas 22±1.6% of the bound radioligand remained bound in the presence of excess synthetic bPTH 1-34. These
data suggested the possibility of a binding site for the carboxy-terminal region of intact PTH, or binding sites selective
for intact hormone. Therefore, additional studies were performed with PTH fragments, PTH 28-53, PTH 35-84, and PTH 53-84.
In contrast to previous studies in other systems, these fragments did not result in significant displacement of125I PTH 1-84. Analysis of binding of125I PTH 1-84 and125I Nle8, Nle18, Tyr34] PTH 1-34 amide, using LIGAND, both indicated a single site model with similar affinities. Thus, the data are consistent
either with multiple receptors with similar affinities or a second binding site for bPTH 1-84 on the same receptor. In the
canine kidney membranes, bPTH 1-84 and synthetic bPTH 1-34 were equipotent in activating adenylate, although the dose-response
curve for bPTH 1-84 was shifted slightly to the right (Kact 2 nm for synthetic bPTH 1-34 versus 5 nm for bPTH 1-84). The present
studies suggest that there are binding sites in canine kidney which are selective for the intact hormone and support the existence
of more than one class of PTH receptors or a second binding site for intact PTH on a single PTH receptor. |
| |
Keywords: | Parathyroid hormone Receptors Kidney membranes Cyclic AMP Adenylate cyclase |
本文献已被 SpringerLink 等数据库收录! |
|