Why do platelets express K⁺ channels?

Potassium ions have widespread roles in cellular homeostasis and activation as a consequence of their large outward concentration gradient across the surface membrane and ability to rapidly move through K⁺-selective ion channels. In platelets, the predominant K⁺ channels include the voltage-gated K⁺ channel Kv1.3, and the intermediate conductance Ca²⁺-activated K⁺ channel KCa3.1, also known as the Gardos channel. Inwardly rectifying potassium GIRK channels and KCa1.1 large conductance Ca²⁺-activated K⁺ channels have also been reported in the platelet, although they remain to be demonstrated using electrophysiological techniques. Whole-cell patch clamp and fluorescent indicator measurements in the platelet or their precursor cell reveal that Kv1.3 sets the resting membrane potential and KCa3.1 can further hyperpolarize the cell during activation, thereby controlling Ca²⁺ influx. Kv1.3^-/- mice exhibit an increased platelet count, which may result from an increased splenic megakaryocyte development and longer platelet lifespan. This review discusses the evidence in the literature that Kv1.3, KCa3.1. GIRK and KCa1.1 channels contribute to a number of platelet functional responses, particularly collagen-evoked adhesion, procoagulant activity and GPCR function. Putative roles for other K⁺ channels and known accessory proteins which to date have only been detected in transcriptomic or proteomic studies, are also discussed.