Preliminary investigations of bony fish--tench (Tinca tinca L.)--erythrocyte insulin receptors.

Abstract

Specific insulin receptors were identified on tench (Tinca tinca L.) erythrocytes. The samples of blood from 3-4 fish per experiment were pooled in summer. Erythrocytes were washed twice with saline solution, then centrifuged and resuspended in the assay buffer. Incubations were carried out in 0.5 ml samples containing 10(9) cells, with addition of 0.03 nmol/l of 125I-pork insulin in the absence or presence of unlabelled pork or salmon insulin (0.05-2000 nmol/l) for 24 h at 4 degrees C. Calculated from seven experiments specific binding of 125I-insulin was 6.2 +/- 0.2% (mean +/- SD). Scatchard analysis of the binding data from insulin radioreceptor assay showed two different binding sites with high (HAIR) and low (LAIR) affinity. KD values were 0.82 +/- 0.17 nmol/l and 2.05 +/- 1.62 mumol/l, and maximal binding capacity (Bmax) 24.9 +/- 1.6 fmol/10(9) cells and 17.5 +/- 12.2 pmol/10(9) cells, respectively (N = 4). If compared with pork insulin, six to seven times more of salmon insulin was required to displace 50% of iodine labelled hormone. Thus, insulin receptors of tench erythrocytes are similar to those described in other species of fish and other lower vertebrates.