The role of N-type Ca2+ channels in regulating excitability of guinea-pig sympathetic neurones.

Abstract Ca 2+ entry through voltage-gated channels activated during the action potential modifies neuronal excitability by activating several types of K + channel. We have determined the effects of Ca 2+ influx through N-type Ca 2+ channels in sympathetic paravertebral neurones of the guinea-pig, using the specific antagonist, ω-conotoxin GVIA. Blockade of large conductance (BK) Ca 2+ -activated K + channels slowed action potential repolarization but did not affect the peak amplitude of the conductance (gKCa1) underlying the afterhyperpolarization. Blockade of small conductance (SK) Ca 2+ -activated K + channels decreased gKCa1 but did not affect action potential repolarization. Blockade of N-type Ca 2+ channels slowed action potential repolarization and reduced the peak amplitude of gKCa1. We conclude that Ca 2+ entry via N-type channels activates both BK and SK channels in guinea-pig sympathetic neurones. This differs from our previous observations in rat sympathetic neurones.