THE EFFECT OF EXTERNAL CESIUM IONS ON THE MUSCLE-FIBER RESTING POTENTIAL IN MEALWORM LARVA (TENEBRIO-MOLITOR L)

The membrane potential of ventral longitudinal muscles of Tenebrio molitor larvae was studied as a function of time and of cesium substituted for all or part of external potassium. The conventional microelectrode technique was applied. The mean value of resting potential was - 47.4 mV in standard physiological saline which did not change significantly with time (90 min). Cesium caused, almost immediately, a significant hyperpolarization of membrane potential the magnitude of which depended on cesium concentration. The presence of external potassium enhanced the effectiveness of cesium action, resulting in more pronounced hyperpolarization. The effect of Cs ions was fully reversible upon washing. These data support the idea that inward potassium current can be activated at resting potential level, at least in some cells, including the muscles studied. It is presumed that this potassium current might have some contribution to the resting membrane potential generation in mealworm larva muscles.