(A and B) Representative images of unstimulated (A) human and (B) mouse platelets probed for F-actin (phalloidin; cyan blue) and aquaporin-1 (AQP1) (magenta) by confocal immunofluorescence microscopy. Two and three platelets are shown in A and B, respectively. (C) Representative immunoblot of human and mouse platelet lysates for AQP1 (at 28 kDa) and glycosylated AQP1 (at 40 kDa), with GAPDH as loading control. m_AQP1, mouse AQP1; h_AQP1, human AQP1. (C) Human adipocyte and human red blood cell lysates were used as negative and positive controls, respectively. Blots show human (h_AQP1) and C57Bl/6 mouse platelet AQP1 (m_AQP1). Immunoblots for AQP1 in mouse platelets show absence of expression in AQP1–/– mice. Blots are representative of 3 independent experiments. (D) Transmission electron microscopy of platelets isolated from WT mice is shown. (E and F) Wild-type mouse platelets processed by the Tokuyasu method for immunogold labeling. AQP1 located on the membrane structures of the open canalicular structure indicated by yellow arrows in reverse contrast images. Data were from platelets obtained from 6 (A and B) or 3 independent experiments (C–F). Scale bar: 3 μm (A and B); 100 nm in (D–F).