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Differences in the operational characteristics of the human recombinant somatostatin receptor types, sst 1 and sst 2 , in mouse fibroblast (Ltk − ) cells
Author(s) -
Castro Sandra W.,
Buell Gary,
Feniuk Wasyl,
Humphrey Patrick P.A.
Publication year - 1996
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1996.tb15238.x
Subject(s) - recombinant dna , somatostatin , fibroblast , somatostatin receptor , biology , receptor , microbiology and biotechnology , cell culture , endocrinology , biochemistry , genetics , gene
1 The human recombinant somatostatin (SRIF) receptors, sst 1 and sst 2 , have been stably expressed in mouse fibroblast (Ltk − ) cells. Two stable clones, LSSR1/20 and LSSR11/13, expressing sst 1 and sst 2 receptors, respectively, have been used to characterize these receptor types using radioligand binding assays as well as measurements of changes in extracellular acidification rates using microphysiometry. 2 [ 125 I]‐[Tyr 11 ]‐SRIF bound to sst 1 and sst 2 receptors expressed in Ltk − cells with high affinity, K d values being 1.52 nM and 0.23 nM, respectively. 3 In Ltk − cells expressing sst 1 receptors, SRIF, SRIF‐28, [D‐Trp 8 ]‐SRIF and CGP 23996 all displaced [ 125 I]‐[Tyr 11 ]‐SRIF binding with high potency (IC 50 values of 0.43‐1.27 nM) whilst seglitide, BIM‐23027, BIM‐23056 and L‐362855 were either weak inhibitors of binding or were ineffective. 4 In contrast MK‐678 (seglitide) and BIM‐23027 were the most potent inhibitors of [ 125 I]‐[Tyr 11 ]‐SRIF binding in Ltk − cells expressing sst 2 receptors with IC 50 values of 0.014 and 0.035 nM, respectively. 5 SRIF and a number of SRIF agonists, including seglitide and BIM‐23027, caused concentration‐ dependent increases in extracellular acidification rates in Ltk − cells expressing sst 2 receptors but not in Ltk − cells expressing sst 1 receptors. The maximum increase in acidification rate produced by SRIF was 11.3 ± 0.7% above baseline (0.1‐0.28 pH unit min −1 ). The relative potencies of the SRIF agonists examined in causing increases in extracellular acidification rates in Ltk − cells expressing sst 2 receptors correlated well with their relative potencies in inhibiting [ 125 I]‐[Tyr 11 ]‐SRIF binding ( r = 0.94). 6 The increase in extracellular acidification produced by SRIF was markedly inhibited by pretreatment of cells with pertussis toxin (100 ng ml −1 ) indicating the involvement of pertussis toxin‐sensitive G proteins. 7 SRIF (1 μ m ) had no effect on basal cyclic AMP levels in Ltk − cells expressing sst 1 or sst 2 receptors nor did it inhibit forskolin stimulated increases in cyclic AMP levels in either cell type. 8 The results from the present study describe the operational characteristics of human sst 2 receptors expressed in Ltk − cells where receptor activation causes increases in extracellular acidification rates. This receptor is coupled to a pertussis toxin‐sensitive G protein. In contrast, activation of sst 1 receptors, at a similar transfection density, did not cause increases in extracellular acidification rates.