Action potentials can propagate along small strands of smooth muscle

Bundles of taenia coli muscle as small as 25 micrometers in diameter were dissected from guinea pigs and incubated in an organ culture media for several days. We found that use of an organ-culture bathing solution greatly extended the in vitro responsiveness as well as survival of such small bundles. Electronmicrographs showed that surviving strands of cells constituted only a very small fraction of the cross section of these bundles. Nonetheless, still they supported propagating nondecrementing action potentials. This means that in some cases strands, only a few cells in cross section, supported propagating action potentials. The long length constant and parallel orientation of cells provide a basis assuming cells act as parallel core conductor segments. For these reasons we have called into question the notion that for propagation to occur there must be a facilitating cooperation between large numbers of smooth muscle cells in parallel. Indeed we suggest that the limiting size for propagation is a strand of single cells.