FUNCTIONAL-ROLE OF LOW-VOLTAGE ACTIVATED DIHYDROPYRIDINE-SENSITIVE CACHANNELS DURING THE ACTION-POTENTIAL IN ADULT-RAT SENSORY NEURONS

Neuronal cell firing is crucial to nerve-nerve communication. The abil ity to produce consecutive action potentials is related to the activat ion of inward currents after each upstroke. If fast Na current is inde ed responsible for the overshoot, it is still unclear which current dr ives membrane voltage to the Na threshold. In this study we present ev idence that in adult rat sensory neurones a dihydropyridine-sensitive Ca channel exists in addition to the well characterized L-type, or hig h-threshold Ca channel. During stimulated action potential trains, L-t ype Ca channels open during the excitation wave, whereas activity of t he other dihydropyridine-sensitive Ca channel was observed primarily b etween action potentials. This second Ca pathway shows remarkably long openings at negative potentials after a series of positive prepulses. The nerve action potential and the repetitive firing work as a physio logical Ca channel facilitation mechanism. Therefore, we suggest that this novel Ca conductance provides inward current, between two consecu tive action potentials, able to modulate the frequency of neuronal bur sts.