Abstract
This chapter describes a study to examine the calcium independence of slow currents underlying spike frequency adaptation. Ganglion cells from Helix aspersa or Lymnaea stagnalis were studied under voltage and current clamp conditions. Either the diminution of spike amplitude and increase in spike width or the decrease in amplitude of peak inward current was used as a test for effective blockage of calcium current. Two types of inward calcium currents have been shown to exist in molluscan neuron somata, a fast component that contributes to the rising phase and peak of the action potential and a slow noninactivating or slowly inactivating component. Only the fast calcium current process was examined in these experiments as a control for calcium entry. It is found that because the interruption of Ca ++ influx markedly affected fast inward current, spike amplitude, and rate of rise, it would appear that the fast calcium component makes the primary contribution to the total Ca ++ influx that these neurons experience. Monitoring this fast component was thought to be an adequate measure of the influence of Ca ++ influx on the slow current mechanism.
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