Evidence for inverse regulation of high and low affinity binding sites for (-)125iodocyanopindolol in human mononuclear leucocytes during epinephrine infusion.
As we have shown earlier (-)125Iodocyanopindolol (125ICYP) binding to beta-adrenoceptors (beta-AR) in human mononuclear leucocytes (MNL) yields evidence for the existence of high affinity (Bhiaff) and low affinity (Bloaff) binding sites. We studied the regulation of these 2 classes of binding sites during 240 min of (-)-epinephrine (EPI) infusion (0.1 microgram/kg/min) (n = 8) in male healthy volunteers. Saturation experiments were performed on MNL membranes with 125ICYP over a large concentration range (1-550 pmol/l). Binding parameters were calculated by computer analysis assuming 2 classes of binding sites. We found a preinfusion value of 830 +/- 50 [sites/cell] (KD = 1.5 +/- 0.2 pmol/l) of Bhiaff binding sites and 5210 +/- 510 [sites/cell] (KD = 420 +/- 80 pmol/l) of Bloaff. During EPI infusion we observed biphasic modulation of the Bhiaff and an inverse modulation of the Bloaff. After 40 min of EPI Bhiaff increased to 1970 +/- 280 [sites/cell] (KD = 4.2 +/- 0.8 pmol/l), whereas Bloaff decreased to 2720 +/- 280 [sites/cell] (KD = 140 +/- 70 pmol/l); despite constant plasma epinephrine concentration (PEC) after 240 min of EPI Bhiaff changed to 1310 +/- 240 [sites/cell] (KD = 2.8 +/- 1.0 pmol/l) vs. 4370 +/- 760 [sites/cell] (KD = 190 +/- 100 pmol/l) Bloaff. These results suggest an interdependent inverse modulation of the 2 classes of binding sites for 125ICYP on MNL during EPI infusion.
Anhäupl
T
T
Universitätsklinik für Anästhesiologie, Universität Ulm, Germany.
Liebl
B
B
Trunk
E
E
Träger
K
K
Ensinger
H
H
Georgieff
M
M
D001667:Binding, Competitive; D004837:Epinephrine / Q000097:blood / Q000494:pharmacology*; D005947:Glucose / Q000096:biosynthesis; D006801:Humans; D020120:Iodocyanopindolol; D007963:Leukocytes, Mononuclear / Q000187:drug effects* / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D010869:Pindolol / Q000031:analogs & derivatives* / Q000378:metabolism; D011869:Radioligand Assay; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism; D012016:Reference Values
D011943:Receptors, Adrenergic, beta; D020120:Iodocyanopindolol; D010869:Pindolol; D005947:Glucose; D004837:Epinephrine