Patch clamp of sarcolemmal spheres from stretched skeletal muscle fibers.

Stretching frog skeletal muscle fibers to the breaking point results in the rapid formation of numerous large spheres of membrane (5-80 microns diam). The surface of the spheres readily forms gigaohm (G omega) seals against patch pipettes, allowing low-noise single-channel recording. Currents recorded from patches isolated from these spheres indicate that they contain a variety of channels including 1) a small Na+-selective channel seen in the presence of veratridine, 2) a K+-selective channel which is blocked by millimolar Mg-ATP, and 3) a relatively large voltage-dependent Cl- channel which is blocked by Zn2+ and limited in selectivity over other anions [PCl/PMOPS = 3.7; MOPS, 3-(N-morpholino)propanesulfonic acid]. These channels have been described previously and have been identified as markers for sarcolemmal (SL) membrane. Accordingly, this method allows rapid and direct recording of channels in the SL membrane without first having to pretreat fibers with proteolytic enzymes to render the SL accessible to patch pipettes.