Concentration dependence of urea-stimulated volume reduction in unswollen reticulocytes. Fresh cells were washed and incubated without prior nystatin treatment in HBS pH 7.4, with no urea (control) or with urea at concentrations indicated. Initial CHCM values reflect in vivo CHMC. (Symbols represent means of 3 independent experiments, with error bars depicting SEM where larger than the symbol.) (A) SS reticulocytes. (B) AA reticulocytes. (C) Dependence on urea concentration of reticulocyte CHCM after 2 hours of incubation for SS (filled symbols) and AA (open symbols) cells.