The Mechanism of Bursting in Aplysia Pacemaker Neurons
Central neurons in the marine mollusc Aplysia generate endogenous bursts of action potentials as part of their normal pattern of activity. This pattern is thought to arise from an alternation of depolarizing waves due to calcium influx and hyperpolarizing waves due to potassium efflux. We have found that the hyperpolarization that terminates bursts and prevents firing until the next burst is caused not by a potassium current, but rather by a calcium-dependent inactivation of the calcium current underlying the depolarizing phase. In addition, we found that the depolarizing afterpotential at the end of each burst is due to a calcium-activated nonspecific cation current. These results help to resolve several controversies surrounding the mechanism of bursting in these neurons.
KeywordsOutward Current Calcium Current Potassium Current Potassium Conductance Calcium Conductance
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