Abstract
Opiates act on mu-receptors to increase the potassium conductance of rat locus coeruleus neurones. Opiates also depress the rate of rise and peak amplitude of calcium action potentials in these cells. The action of opiates on calcium action potentials was prevented by two procedures which blocked the opiate-induced potassium current, intracellular caesium and extracellular barium. This indicates that the opiate reduction in calcium entry is secondary to an increased potassium current.