Figure 2.
Dependence of bursting properties on INaP but not on Ih. A1, Total membrane current (top traces) evoked by a triangular voltage ramps (bottom trace) from −70 to +10 mV and back to −70 mV over 10 s, before (black trace) and after removing the extracellular calcium (dark gray trace). A subsequent application of TTX (1 μm) abolished the current (light gray trace). A2, A3, The current leak-subtracted was plotted as a function of command voltage in the presence (A2) and absence of extracellular calcium (A3). The arrows indicate direction of voltage changes. B1, B2, Effects of sodium currents blockade on bursting properties. A ventromedial interneuron displaying bursting properties in [Ca2+]o-free ACSF is illustrated before (B1) and 20 min (B2) after the application of strychnine (1 μm), bicuculline (20 μm), and kynurenate (1.5 mm). B3 and B4 illustrate the effect of a progressive blockade of sodium currents on the burst generation, 5 and 10 min after the onset of TTX application (1 μm), respectively. C1, C2, Effects of a blockade of INaP on bursting properties. Another ventromedial interneuron exhibiting bursting properties in [Ca2+]o-free ACSF is illustrated before (C1) and 15 min (C2) after the application of riluzole (10 μm). Note in C2 that the amplitude of spikes was not affected. In C3, a recovery of bursting properties is illustrated after a 1 h washout period. D1, D2, Effects of a blockade of Ih on bursting properties. A ventromedial interneuron exhibiting bursting properties in [Ca2+]o-free ACSF is illustrated before (D1) and 15 min (D2) after the application of ZD 7288 (20 μm). ZD 7288 blocked the depolarizing sag (arrowhead) induced by a hyperpolarizing current pulse of −0.4 nA.