Calcium-dependent after-potentials in visceral afferent neurones of the rabbit

Intracellular recordings were made from neurones in nodose ganglia excised from rabbits. In C neurones, 1-60 action potentials were followed by an after-hyperpolarization with a peak amplitude of 16 mV and a time constant of decay ranging from 3 to 10 s. In A neurones, the action potentials were followed only by a brief (up to 50 ms) after-hyperpolarization. The after-hyperpolarization was associated with an increase in the membrane conductance to potassium ions; it reversed polarity at the potassium equilibrium potential. The increase in conductance following the action potentials was blocked by removal of calcium ions, or addition of cobalt to the extracellular solution. Intracellular injection of ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) abolished the after-hyperpolarization; intracellular injection of calcium mimicked the after-hyperpolarization. It is concluded that calcium entry during the action potential leads to a long-lasting increase in potassium conductance in visceral afferent C neurones.