Ischaemia causes externalization of endothelin-1 binding sites in rat cardiac membranes

Specific, high affinity binding sites for iodinated endothelin-1 ([125I]-ET-1) were identified in crude plasma and light membrane fractions harvested from aerobically perfused and ischaemic rat hearts, to determine whether the ischaemia-induced increase in binding site density (Bmax) involves externalization of the sites. In crude plasma membranes Bmax increased after 60 min ischaemia, from 113.5 +/- 2.15 to 180.6 +/- 4.67 fmol/mg protein (p less than 0.01). In the light membranes, the Bmax fell, from 94.7 +/- 8.70 to 63.80 +/- 6.26 fmol/mg protein (p less than 0.05). Hill coefficients and selectivity of both membrane fractions were unchanged. These results are interpreted as meaning that ischaemia causes externalization of cardiac [125I]-ET-1 binding sites.