Voltage-dependent channels of human muscle cultures

Cultures were grown from satellite cells obtained from biopsies of normal children and of boys having Duchenne muscular dystrophy (DMD). Patch-clamp recordings were obtained from mononucleated cells and from young myotubes containing up to five nuclei. Four current types were distinguished. Na currents had a maximum amplitude near -10 mV and a half inactivation point near -60 mV. Single channel currents observed in isolated patches had a main unit size of 1.8 pA at -30 mV. Voltage dependent outward K currents were blocked by applying tetraethylammonium to the bath solution. In some cells, outward currents had a rather slow activation and did not inactivate. In other cells, activation was faster, and the currents inactivated. At large positive potentials, another K current was activated. The corresponding channels displayed large unit steps in isolated patches. Hyperpolarizing voltage pulses elicited in about one third of the cells inward rectifier currents. All currents types were found with similar characteristics in normal and DMD cultures. Whole cell results were very variable. Cells displayed various combinations of the four kinds of currents. To understand the origin of this diversity, clonal cultures were investigated. Clones displayed more homogeneous electrical properties than standard cultures, suggesting the presence of various types of stem cells in the non-clonal cultures.