What is the Opposite of a Receptor Reserve?

There are semilogarithmic (lg-) concentration-response sigmoids with slopes exactly representing the opposite asymmetry of that encountered in the case of a receptor reserve (reserve: large curvature in the left part of the curve and narrow curvature in the right part; opposite: narrow curvature in the left part of the curve and large curvature in the right part). In addition, the binding K < SUB>d < /SUB>s of agonists are smaller than their EC < SUB>50 < /SUB> in such curves. Using experimental concentration-response data a non-linear fitting model of a receptor "antireserve" was developed which is the topic of the present paper. This model reflects the possibility of a subthreshold preactivation of a signaling system. Hypothetically, only after exceeding this threshold a receptor-mediated response takes place.