Expression of a voltage-dependent potassium current precedes fusion of human muscle satellite cells (myoblasts).

Using the whole-cell recording patch clamp technique in clonal cultures of human muscle satellite cells (SC), we studied a voltage-gated potassium current analogous to the delayed rectifier current (IKdr) described in adult human skeletal muscle. This current was absent in proliferating SC cultured in a growth medium containing 15% serum, except when the SC approached the end of their replicative life (between 77 and 124 days in culture); at that time, approximately 50% of the SC possessed IKdr. In contrast, IKdr was expressed within less than 4 days in approximately 70% of the SC cultured in a serum-free medium (SFM) and within 24 h in differentiating medium. We believe that IKdr may be a characteristic feature of fusion-component SC and that it may be involved in the fusion process for the following reasons: 1) after the transfer in differentiating medium, cultures of SC in which the expression of IKdr was previously promoted by exposure to SFM were found to fuse immediately, without the initial 24 h lag time observed in control sister cultures; 2) in the latter "naive" SC, IKdr was expressed during the first day in differentiating medium, before SC began to fuse; 3) most of the SC that did not fuse even after weeks of exposure to differentiating medium did not express IKdr; 4) TEA, at a concentration of 3 mM, reduces the amplitude of IKdr by 55% and the fusion index by 55-67%.