An analysis of the bursting behaviour of the Aplysia R sub(15) neurone during exposure to normoxia and hypoxia with and without external calcium present

Membrane potentials (E sub(M)), interburst intervals (IBI), burst durations (BD), the numbers of spikes within a burst, and the amplitudes of the burst pacemaker potentials (BPP) were measured in two groups of R sub(15) neurones under conditions of 20, 10 and 5% oxygen and under nitrogen equilibration in suffusates with either Ca super(2+) or Mg super(2+) present (Groups I and II). Under normal extracellular Ca super(2+) conditions, E sub(M) and the amplitude of the BPP for Group I R sub(15) neurones increased progressively during hypoxia and reoxygenation. In the absence of external calcium, the normal bursting pattern of Group II R sub(15) neurones was interrupted. No consistent relationships were observed among BD, IBI, and the number of spikes per burst with respect to E sub(M) or BPP. Hypoxia may alter the resting permeability of R sub(15) to potassium as well as having ephaptic effects.