Comparative levels of P2X₁ receptor protein and Na⁺,K⁺-ATPase α subunit in membranes from platelets, neutrophils, and mononuclear leukocytes. Adjacent lanes were loaded with 5, 15, or 30 μg of total membrane protein isolated from the indicated blood cell types (platelets, neutrophils, mononuclear). (A) The immunoblot initially probed with P2X₁receptor antiserum (<<<, 95 kD; <<, 60 kD). (B) The same blot stripped and reprobed with MoAb 9A7 against the α subunit of the Na⁺,K⁺-ATPase. (◂), 110 kD α subunit.