Intercellular communication between bone marrow stromal cells and CD34(+) haematopoietic progenitor cells is mediated by connexin 43-type gap junctions

The existence of functional gap junctions between haematopoietic progenitor cells (HPCs) and stromal cells of the haematopoietic microenvironment in t he human system is a controversial issue. Primary CD34(+) HPCs isolated fro m leukapheresis products were co-incubated with the human fibroblastoid bon e marrow stromal cell line L87/4 in short-term liquid culture. Using the hi ghly sensitive double whole-cell patch-clamp technique, we found that the m ajority (91%) of CD34(+) HPCs are electrically coupled to L87/4 cells. Impo rtantly, efficient coupling was observed within 1 h of the attachment of CD 34(+) HPCs to plastic adherent L87/4 cells. By comparison, homologous cell pairs formed by L87/4 cells exhibited a significantly higher electric coupl ing. Analysis of single-channel conductances revealed an electric profile c haracteristic of connexin 43 (Cx43)-type gap junctions for both homologous and heterologous cell pairs. The Cx phenotype was confirmed using Cx43-spec ific monoclonal antibodies in a flow cytometric assay and reverse transcrip tion polymerase chain reaction (RT-PCR) for the detection of Cx43 mRNA. Fin ally, the electrophysiological studies were complemented by dye-transfer ex periments using the recently described 'parachute' technique that allows th e monitoring of dye diffusion without disruption of the plasma membrane. Ta ken together, our data indicate that functional Cx43-type gap junctions exi st between stromal cells and immature HPCs and, thus, may provide an import ant regulatory pathway in haematopoiesis.