SUPPRESSION OF RHYTHMIC DISCHARGES OF MEDULLARY NEURONS IN ORGANOTYPIC CULTURES OF NEWBORN RATS BY CALCIUM-ANTAGONISTS

The contribution of transmembrane calcium flux to the generation of pe riodic bioelectric activity in cultured organotypic medullary tissue o f 6 day old rats was determined by adding calcium antagonists (CA) to the recording saline and by lowering the calcium concentration of this saline. Organic CA flunarizine and verapamil (50-100 mu mol/l) revers ibly suppressed rhythmic discharge and diminished the CO2 response of medullary neurones within 30-60 min. Inorganic CA cobalt and magnesium exerted the same effects within a few minutes. After lowering the cal cium concentration rhythmic activity became unstable, but recovered on exposure to increased CO2 concentration, the excitatory effect of whi ch was strongly reduced. These findings point to a significant role fo r transmembrane calcium flux and intracellular calcium concentration i n sustaining both periodic activity and the CO2 response of medullary neurones.