THE TEMPERATURE-DEPENDENCE OF HIGH-THRESHOLD CALCIUM-CHANNEL CURRENTSRECORDED FROM ADULT-RAT DORSAL RAPHE NEURONS

The temperature dependence of HVA calcium channel currents, using bari um as the charge carrier, was studied in acutely isolated adult rat do rsal raphe neurones. Current amplitude was found to be highly sensitiv e with a Q(10) of between 1.7 and 2.5. The most sensitive component of current is that that is activated from hyperpolarized holding potenti als, and inactivates during a 200 msec test pulse. The least sensitive is the more sustained current elicited from depolarized potentials. I ncreases in temperature were also found to cause an irreversible shift in the current-voltage relationship in the hyperpolarizing direction. By far the most temperature-sensitive property was the activation tim e constant with an extraordinary Q(10) of between 10 and 12. This was not significantly affected by holding potential, though the time const ant itself is dependent on the test potential. Increases in temperatur e to 25 degrees C or above revealed a fast inactivating component, not seen at lower temperatures. These findings suggest that there are at least three components of HVA current in dorsal raphe neurones. In add ition, the remarkably high Q(10) for activation kinetics suggests that the processes underlying calcium channel current activation are multi faceted and complex. The following paper puts forward a new hypothesis which attempts to explain the way in which neurotransmitters modulate the activation kinetics of HVA calcium channel currents.