Influence of sodium on the alpha 2-adrenergic receptor system of human platelets. Role for intraplatelet sodium in receptor binding.

摘要: The affinity of many types membrane receptors for agonists is decreased by Na+ in radioligand binding experiments. We studied the alpha 2-adrenergic receptor human platelets to determine whether acts at an intracellular or extracellular location. content intact isotonic saline buffer was 38 nmol/10(8) platelets. This increased 138 with Na+-selective ionophore monensin and 13 incubation a Na+-free buffer. Epinephrine-induced platelet aggregation addition buffer, while thrombin-induced unaltered either condition. Monensin, gramicidin, ouabain (which all intraplatelet Na+) caused 2-3-fold increase Kd epinephrine (in competition [3H]yohimbine) on Conversely, 2-3-fold. These experiments suggest that changes alter binding. Control studies eliminated several alternative explanations effect binding: 1) altered only not membranes; 2) although depolarized (assessed [3H]methyltriphenylphosphonium uptake), other depolarizing conditions did change binding; 3) may pH (by exchanging H+) such 2-receptors membranes epinephrine, opposite produced conclude alterations concentration epinephrine. results key role modulating cell surface vivo.