[Effects of carbamylcholine and impromidine on cell cycle state of CFU-S]

In normal steady-state conditions, there was less than 10% loss of CFU-S due to hydroxyurea (HU, 10(-3) mol/L). The CFU-S killed by HU was greatly increased after bone marrow cells of LACA mice were exposed in vitro to carbamylcholine (Cach) (10(-13)-10(-9) mol/L) and impromidine (Impro) (10(-9)-10(-4) mol/L). They were 32.8 (Cach) and 38.4% (Impro) for day 9 CFU-S; 60.6 (Cach) and 49.5% (Impro) for day 13 CFU-S at plateau phase. The effects were blocked by antagonists of cholinergic N receptor d-tubocurarine and of histamine H2 receptor cimetidine, respectively. The different sensitivity to agonists between CFU-S forming early spleen colonies and late colonies may reflect differences in receptor density on the surface of haemopoietic stem cells or receptor activity. The studies provide additional evidence suggesting the heterogeneity of pluripotent haemopoietic stem cells.