Suppression of rhythmic discharges of medullary neurones in organotypic cultures of new-born rats by calcium antagonists.

The contribution of transmembrane calcium flux to the generation of periodic bioelectric activity in cultured organotypic medullary tissue of 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 mumol/l) reversibly 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 calcium concentration rhythmic activity became unstable, but recovered on exposure to increased CO2 concentration, the excitatory effect of which was strongly reduced. These findings point to a significant role for transmembrane calcium flux and intracellular calcium concentration in sustaining both periodic activity and the CO2 response of medullary neurones.