CHARACTERISTICS OF ACTIONPOTENTIAL AND THEIR UNDERLYING OUTWARD CURRENTS IN MAMMALIAN TASTE RECEPTOR CELLS

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CHARACTERISTICS OF ACTION POTENTIAL AND THEIR UNDERLYING OUTWARD CURRENTS IN MAMMALIAN TASTE RECEPTOR CELLS

Many rat taste receptor cells conduct action potentials(APs).APs had a mean threshold of -35 mV(n=95 cells)and a spike height of 52mV above threshold in current clamp(hold= -80mV).Aps could be classified into two significantly different (P<0.001) groups-fast,with short half-time durations and large outward currents (mean1.3 ms and 2.7nA),and slow,with long duration and small outward currents(mean9.2ms and 0. 29nA).AP upstrokes were conducted by TTX-sensitive sodium currents whereas the downstroke by TEA-blockable outward currents. Voltage dependent analysis of outward current separated transient and sustained components.The transient component was specifically blocked by 4-AP(1mmol/L).A calcium-dependent outward component was also revealed modulating voltage and external calcium concentration.The fast recovery phase of the AP appears related the sustained outward current whereas the after hyperpolarization(AHP) was blocked by 4AP suggesting a significant contribution of the transient component.Forskolin (FSK),which elevates cAMP,reversibly blocked the majority of the sustained current without influencing the transient. FSK greatly exaggerated the AHP without changing the spike height or duration. These data suggest that several components of the outward current contribute specifically to the gustatory AP and that the AP may be modulated by cyclic nucleotides.