Facilitation of plateau potentials in turtle motoneurones by a pathway dependent on calcium and calmodulin

1. The involvement of intracellular calcium and calmodulin in the modulatio n of plateau potentials in motoneurones was investigated using intracellula r recordings from a spinal cord slice preparation. 2. Chelation of intracellular calcium with BAPTA-AM or inactivation of calm odulin with W-7 or trifluoperazine reduced the amplitude of depolarization- induced plateau potentials. Inactivation of calmodulin also inhibited facil itation of plateau potentials by activation of group I metabotropic glutama te receptors or muscarinic receptors. 3. In low-sodium medium and in the presence of tetraethylammonium and tetro dotoxin, calcium action potentials evoked by depolarization were followed b y a short hyperpolarization ascribed to the calcium-activated non-selective cationic current (I-CAN) and by a dihydropyridine-sensitive afterdepolariz ation. The amplitude of the afterdepolarization depended on the number of c alcium spikes and was mediated by L-type calcium channels. 4. The dihydropyridine-sensitive afterdepolarization induced by calcium spi kes was reduced by blockade of calmodulin. 5. It is proposed that plateau potentials in spinal motoneurones are facili tated by activation of a calcium-calmodulin-dependent pathway.