A selective biotinylated probe for V_1a vasopressin receptors

We have designed and synthesized a biotinylated vasopressin antagonist which is a selective probe for studying the V_1a subtype of vasopressin receptor. Initially we synthesized the novel vasopressin analogue d(CH₂)₅Tyr(Me)²LysNH₂⁹AVP (ALVP). Biotinamidocaproate was subsequently coupled to the ε{lunate}-amino group of ALVP to generate the novel biotinylated probe d(CH₂)₅Tyr(Me)²Lys(Nε{lunate}-biotinamidocaproate) NH₂⁹AVP (ALBtnVP). Pharmacological characterization of ALVP and ALBtnVP established that both ligands were high affinity antagonists at V_1a receptors, and that both displayed marked V_1a/V₂ selectivity. The observation that receptor-bound ALBtnVP was bi-functional, and thereby able to bind conjugated derivatives of avidin or streptavidin, allowed ALBtnVP to be utilized as a selective probe for V_1a receptors. This strategy allowed the visualization of V_1a receptors on the surface of WRK-1 cells and hippocampal neurons, by using streptavidin-gold with electron microscopy and fluorescein-avidin with light microscopy. We conclude that ALBtnVP is a useful probe for V_1a receptors.