Characteristics of 5-hydroxytryptamine transport in pancreatic islets.

1 Transmembrane transport of 3H-labelled 5-hydroxytryptamine (5-HT) by isolated pancreatic islets of non-inbred ob/ob mice was studied. 2 5-HT was vigorously accumulated in a temperature-dependent way by the islet cells. 3 Studies of the concentration-dependence of [3H]-5-HT uptake revealed complex kinetics with one component being saturated at 1 to 3 microM 5-HT (apparent association constant 0.6 x 10(6) M(-1) and the other non-saturated up to 1 mM 5-HT. 4 The saturable uptake was inhibited by Na+-deficiency and metabolic poisoning with 2,4-dinitrophenol and antimycin A, whereas the non-saturable component was not affected. 5 Omission of K+, Ca2+ or Mg2+ did not affect the uptake rate. 6 It is concluded that 5-HT is taken up by pancreatic beta-cells by mechanisms very similar to those observed in thrombocytes and neurones.