Temperature-sensitive high affinity [3H]tryptamine binding sites in rat brain.
The influence of prior incubation on [3H]tryptamine binding was investigated in rat brain synaptic plasma membranes. A 55 min preincubation of the membranes at 37 degrees C induced an approx. 2.4-fold increase in the specific binding of [3H]ligand to the subsequently washed preparations and this phenomenon was quite temperature-dependent. On the other hand, the proportion of nonspecific binding sites was significantly decreased by 70% of the original sites within 20 min of the start of preincubation. Pargyline, ascorbic acid, EGTA, metal ions (Ca2+, Mg2+, Na+) and guanine nucleotides, included in the preincubation buffer, were all inactive on the stimulation of [3H]tryptamine binding, while the pretreatment of membranes with glutaraldehyde antagonized the augmentation of this binding. Furthermore, it was revealed that the Scatchard plot of the [3H]tryptamine binding preincubated at 0 degree C conformed to a straight line (KD = 33.1 nM, Bmax = 543 fmoles/mg protein), whereas a curvilinear Scatchard plot was obtained at 37 degrees C preincubation. Nonlinear regression analysis of the latter resulted in apparent KD (nM) & Bmax (fmoles/mg protein) values of 0.45 & 102.7 and 33.7 & 603.4 for the high and low affinity sites, respectively. All these observations lead to the inference that the preincubation-induced increase in [3H]tryptamine binding (i.e., nearly high affinity proportion of sites) may occur as a result of temperature-sensitive interconvertible conformational changes.
Karasawa
A
A
Serikyaku
S
S
Ishitani
R
R
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D002412:Cations; D005976:Glutaral / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D010293:Pargyline / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism; D013570:Synaptic Membranes / Q000378:metabolism; D013696:Temperature; D014363:Tryptamines / Q000378:metabolism*
D002412:Cations; D011985:Receptors, Serotonin; D014363:Tryptamines; C030820:tryptamine; D010293:Pargyline; D008274:Magnesium; D001205:Ascorbic Acid; D005976:Glutaral