CALCIUM CURRENTS AND CALCIUM-DEPENDENT POTASSIUM CURRENTS IN MAMMALIAN MEDULLARY RESPIRATORY NEURONS

1. Respiratory neurones of mammals are rhythmically active because the ir membrane potential fluctuates periodically over a voltage range of - 70 to - 55 mV. These respiratory drive potentials lead to periodic d ischarges of bursts of action potentials lasting for 1-2 s. The neuron al processes stabilizing this rhythmic activity involve excitatory and inhibitory synaptic processes that interact with specific membrane pr operties of the postsynaptic neurones. In the present experiments, per formed on dorsal and ventral groups of respiratory neurones under in v ivo and in vitro conditions, we verified the modulating feature of suc h intrinsic neuronal properties. 2. Intrinsic neuronal properties invo lve Ca2+ Mechanisms that lead to intracellular Ca2+ accumulation, and consequently to activation of Ca2+-dependent K+ currents. 3. Blockade of intracellular Ca2+ accumulation significantly changed the amplitude and pattern of respiratory drive potentials, and blocked initial hype rpolarizing shifts of the membrane potential following each period of synaptic activation. 4. The data demonstrate that postsynaptic activit ies and action potential discharges activate low and high voltage-acti vated Ca2+ currents leading to intracellular Ca2+ accumulation and to activation of Ca2+-dependent K+ currents that significantly modulate t he voltage response of medullary respiratory neurones to on-going syna ptic activation. These intrinsic membrane properties also seem to be i nvolved in the processes controlling termination of rhythmic burst dis charges.