Heterogeneity of the afterhyperpolarization of sympathetic preganglionic neurons.

The components of the afterhyperpolarization (AHP) of the sympathetic preganglionic neuron were studied in the slice of the upper thoracic spinal cord of the cat. In this neuron, the AHP consists of a fast (fAHP) followed by a slow (sAHP) component. While the fAHP had similar time course in all neurons studied (n = 116), the sAHP had considerable variability. Two components could be identified and the variability resulted from variation in the relative magnitude of these. Fifteen percent of neurons showed only an early component of the sAHP, 16% showed only a late component, and 69% showed both components. The early component of the sAHP was selectively blocked by apamin and d-tubocurarine, while the late component was selectively blocked by ryanodine, procaine or phenylephrine.