ACTIVE CURRENTS REGULATE SENSITIVITY AND DYNAMIC-RANGE IN C-ELEGANS NEURONS

Little is known about the physiology of neurons in Caenorhabditis eleg ans. Using new techniques for in situ patch-clamp recording in C. eleg ans, we analyzed the electrical properties of an identified sensory ne uron (ASER) across four developmental stages and 42 unidentified neuro ns at one stage. We find that ASER is nearly isopotential and fails to generate classical Na+ action potentials. Rather, ASER displays a hig h sensitivity to input currents coupled to a depolarization-dependent reduction in sensitivity that may endow ASER with a wide dynamic range . Voltage clamp revealed depolarization-activated K+ and Ca2+ currents that contribute to high sensitivity near the zero-current potential. The depolarization-dependent reduction in sensitivity can be attribute d to activation of K+ current at voltages where it dominates the net m embrane current. The voltage dependence of membrane current was simila r in all neurons examined, suggesting that C. elegans neurons share a common mechanism of sensitivity and dynamic range.