Modified somatostatins as inhibitors of a multispecific transport system for bile acids and phallotoxins in isolated hepatocytes

K. Ziegler, M. Frimmer, H. Kessler, I. Damm, V. Eiermann, S. Koll, J. Zarbock

Publikation: Beitrag in FachzeitschriftArtikelBegutachtung

63 Zitate (Scopus)

Abstract

Somatostatin inhibits the uptake of phallotoxins and of cholic acid in isolated liver cells in a concentration-dependent manner. The inhibition is independent on the preincubation period and fully reversed by switching to a somatostatin-free buffer. Concentrations needed for 50% inhibition decreased 30-80-fold when somatostatin was modified by variation of its amino acid sequence. Some cyclic hexa- or penta-peptides inhibited both kinds of transport more strongly as the original (14 amino acid) somatostatin did. Three of the analogs showed a 2-3-fold higher potency than the others. The most potent compound (cyclo (Phe-Thr-Lys-Trp-Phe-d-Pro) 1 was studied in detail. The IC50 for the initial uptake of phallotoxin (6 μM) or of cholate (6 μM) was 1.5 or 3 μM, respectively. 1 inhibited the uptake of cholate in a competitive manner. The inhibition was independent on the preincubation time, but in contrast to somatostatin not fully reversible after a preincubation of 35 min. Somatostatin as well as its analogs prevented binding of isothiocyanatobenzamido [3H]cholate (an affinity label of the cholate transporter) to isolated plasma membranes from rat liver. The transport inhibition of cholate uptake is unlikely to be a hormonal effect of somatostatin, because the concentrations needed are approx. 1000-fold higher than circulating levels; however, it is apparently possible to increase the inhibitory potency on the tested transport system by modification of the sequence without increase of the well-known hormonal effects (Designing Activity and Receptor Selectivity in Cyclic Peptide Hormone Analogs, Kessler, H., 18th Ervag Conference, Brussels, 1983).

OriginalspracheEnglisch
Seiten (von - bis)86-93
Seitenumfang8
FachzeitschriftBiochimica et Biophysica Acta - Molecular Cell Research
Jahrgang845
Ausgabenummer1
DOIs
PublikationsstatusVeröffentlicht - 22 Apr. 1985
Extern publiziertJa

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