ROLE OF THE CYTOSKELETON IN THE REGULATION OF CL- CHANNELS IN HUMAN EMBRYONIC SKELETAL-MUSCLE CELLS

The effects of volume change and cytoskeleton manipulation on the Cl- channels in human embryonic skeletal muscle cells were studied. Trypsi nation, used for production of myoballs, changes the channel propertie s only a little. When the external osmolarity was reduced from 300 to 270 mosmol/l, the specific Cl- conductance, g(Cl) (at -80 mV) of myoba lls increased from 5.1 +/- 1.9 to 30.4 +/- 12.2 mu S/cm(2) (SD; n = 6) within 15 min. Concomitantly, the kinetics of Cl- currents, elicited by clamping the membrane potential from a negative to positive values, changed from activation and subsequent slow inactivation to instantan eous activation with fast inactivation. G protein activation, protein kinase action or [Ca2+](i) elevation seemed not to be involved in thes e effects. Similar changes were produced in the absence of a transmemb rane osmotic gradient by 500 nM intracellular cytochalasin D (g(Cl) = 34.3 +/- 10.3 mu S/cm(2); n = 6) or 12.5 mu M colchicine (g(Cl) 15.4 /- 1.4 mu S/cm(2); n = 5). When the external osmolarity was increased to 418 mosmol/l, 1 mu M cytochalasin D did not affect g(Cl). In four o f six cell-attached patches the open probability of the intermediate C l- channel was increased after reduction of the bath osmolarity. In in side-out patches, the drugs increased the open probability of the chan nels. It is concluded that the Cl- channels are under control of the c ytoskeleton.