Depolarizations of cultured rat cortical neurons by Tat30-86. A, Tat30-86 (50 nM) applied by superfusion produced a small membrane depolarization with no detectable changes in membrane resistance. The broken line denotes resting membrane potential. B, a higher concentration of Tat30-86 (500 nM) produced a long-lasting depolarization accompanied by intense discharge and a marked decrease in membrane resistance. C, Tat30-86 (1000 nM) induced a long-lasting depolarization in a neuron pretreated with tetrodotoxin (TTX; 0.5 μM). A, B and C represent actual recordings from three different neurons. Downward deflections superimposed on the membrane potential are hyperpolarizing electrotonic potentials induced by constant current pulses (30 pA, 300 ms) and are used to monitor membrane resistance changes. D, concentration-response relationship of Tat-induced depolarizations; data points represent mean ± S.E. of 3-6 neurons. E. Depolarizations of cerebral cortical neurons induced by Tat 30-86 as monitored by optical imaging using DiSBAC4(3); the depolarization is slightly reduced by pretreatment with AP-5 and CNQX; recordings are from two different neurons.
Neuronal excitability increase by Tat30-86. A, a cortical neuron discharged 4 action potentials in response to a step depolarizing current pulse (30pA, 500ms, not shown). Tat30-86 (10 nM) increased the number of action potentials to 8 in response to the same depolarizing stimulus (lower panel). B, stimulus-response curves obtained before and after perfusion of 10 nM Tat (n=4); * denotes P<0.05.
Comparison of Tat30-86-induced responses of rat cerebral cortical neurons in normal Krebs and Ca2+-free Krebs. A, superfusion of Tat (500 nM) produced a membrane depolarization accompanied by a small decrease in input resistance. B, this neuron was perfused with Ca2+-free Krebs solution for 5 min prior to administration of Tat30-86. C, normalized Tat-induced depolarizations in normal Krebs solution (control, n=4) and Ca2+-free Krebs solution (n=4). Asterisk indicates a statistically significant difference (P< 0.05).
I-V relationship of Tat30-86-induced currents in normal Krebs solution and Ca2+-free Krebs solution. A, steady-state I-V curve before (open triangle, control)) and after (filled triangle) application of Tat (500 nM). B, the reversal potential of Tat-induced current in this neuron was about -30 mV. C, steady-state I-V curve before (open triangle, control) and after (filled triangle) application of Tat30-86 (500 nM) in a neuron perfused with Ca2+-free Krebs solution for 10 min before application of Tat. D, Tat-induced current did not reverse between -140 and 0 mV. The neuron was held at -60mV.
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