Ligand internalization and recycling by human recombinant somatostatin type 4 (h sst4) receptors expressed in CHO-K1 cells

摘要: There is controversy as to whether somatostatin sst(4) receptors internalize. In this study, CHO-K1 cells expressing human receptor (CHOsst(4) cells) internalized [(125)I]-[(11)Tyr]-SRIF in a time-dependent manner, reaching steady state at 60 min (1.4+/-0.1x10(4) molecules per cell). Internalization was blocked by hypertonic sucrose (0.5 M), ATP depletion or decreasing the temperature 4 degrees C. of also inhibited (pIC(50) values) increasing concentrations SRIF (7.74), L-362855 (6.27) and NNC-296100 (6.50) with pIC(50) values approximately 10 fold lower than those obtained for inhibition binding membrane homogenates. Internalized ligand recycled rapidly extracellular media (t(1/2) 3.9+/-0.7 min) only 6.8+/-0.6% radioactivity remaining cell after 45 min. Confocal microscopy permeabilized, HA-epitope tagged CHOsst(4) labelled Cy-3 conjugated antibody revealed little internal immunostaining (1 microM) treatment, consistent small proportion (3.5%) estimated be radioimmunoassay. summary, clathrin- ATP-dependent manner subsequent rapid recycling medium. Rapid consequent low any one time may explain inability visualize confocal microscopy. It seems unlikely therefore that marked desensitization observed following treatment can accounted decrease surface expression.