ROLES OF ACETATE AND PHOSPHATE IN THE SUCCESSFUL STORAGE OF PLATELET CONCENTRATES PREPARED WITH AN ACETATE-CONTAINING ADDITIVE SOLUTION

The development of a synthetic medium for platelet storage is an important goal in transfusion medicine. Its use would make large volumes of plasma available for fractionation and might improve the quality of platelets after storage. Several investigators have described successful storage in media containing acetate. The previous work of the authors showed that platelet concentrates (PCs) can be stored successfully for 5 days at 22-degrees-C by using an additive solution (Seto sol) to replace 80 to 95 percent of the plasma usually employed as a suspending medium. Seto sol contains 23 mM (23 mmol/L) sodium acetate and 25 mM (25 mmol/L) sodium phosphate. The roles of acetate and phosphate in achieving successful platelet storage were studied in the work reported here. The concentration of acetate decreased linearly for 7 days at 0.61 +/- 0.11 mumol per day per 10(9) platelets in parallel with the disappearances of l-C-14 or 2-C-14 acetate. There was no disappearance of tritiated acetate from PCs or of 1-C-14 acetate from platelet-free mixtures of plasma and Seto sol, which suggests that the disappearance of C-14 acetate from PCs reflected oxidation to CO2, which could leave PCs through the walls of the plastic container. Since 02 consumption was 1.47 mumol per day per 10(9) platelets, and the oxidation of a molecule of acetate requires 2 molecules of oxygen, acetate oxidation accounted for approximately 85 percent of oxygen consumption by platelets. The pH of PCs stored in Seto sol was nearly constant for 7 days, whereas, without acetate, it fell to 6.4 +/- 0.1 on Day 5. It is known that the oxidation of one molecule of acetate produces one molecule of CO2 and one molecule of bicarbonate. Indeed, in PCs in Seto sol, there was an elevation of bicarbonate concentration of 1.4 mEq per L by Day 3, which suggests bicarbonate production. Thus, acetate acts as both a substrate for oxidative metabolism and a source of buffer. However, in 5 of 11 PCs stored in Seto sol without phosphate, the pH dropped to 6.2 within 3 days. PCs that showed a drop in pH were those in which the content of plasma carryover during PC preparation was less than 12.5 percent of the suspending medium. It appears that a buffer system in addition to that provided by acetate is necessary to the maintenance of platelet integrity during storage when plasma carryover is low.