Seasonal patterns in platelet ligand binding are related to membrane proteins

A seasonal pattern of platelet [3H]imipramine (3H-IMI) binding was explained by a similar but inverted pattern in membrane protein levels in repeated measures of 20 normal volunteers. No seasonal pattern was evident when 3H-IMI binding was expressed on the basis of surface area rather than membrane protein. Platelet Bmax levels in 50 depressed patients were lower than those of controls when values were expressed in terms of platelet surface area. The results support previous reports of low Bmax values in unipolar major depression, but indicate that seasonal changes in 3H-IMI binding are due to fluctuations in membrane protein and not to changes in the number of receptive sites. The present findings also have similar implications for other platelet measures expressed in terms of membrane protein.