RAPID COMMUNICATION Muscarinic Inhibition of Persistent Na Current in Rat Neocortical Pyramidal Neurons

Mittmann, Thomas and Christian Alzheimer. Muscarinic inhibibuffered oxygenated saline solution containing 19 U/ml papain. Whole cell currents were evoked and recorded using an Axopatch tion of persistent Na current in rat neocortical pyramidal neurons. J. Neurophysiol. 79: 1579–1582, 1998. Muscarinic modulation of 200 amplifier in conjunction with a TL-1 interface and pClamp 6.0 software (all from Axon Instruments) . Current signals were persistent Na current (INaP) was studied using whole cell recordings from acutely isolated pyramidal cells of rat neocortex. sampled at 2–5 kHz and filtered at 1 kHz (03 dB). All recordings were performed at room temperature (21–24 7C). Membrane poAfter suppression of Ca and K currents, INaP was evoked by slow depolarizing voltage ramps or by long depolarizing voltage tential was corrected for liquid junction potential. Throughout the experiments, leakage and capacitive currents were determined from steps. The cholinergic agonist, carbachol, produced an atropinesensitive decrease of INaP at all potentials. When applied at a saturathyperpolarizing voltage steps and eliminated using the built-in compensation circuits of the amplifier. Experiments were started ing concentration (20 mM), carbachol reduced peak INaP by 38% on average. Carbachol did not alter the voltage dependence of INaP when stable INaP responses were obtained, typically 5–8 min after whole cell access was established. During the initial stabilization activation nor did it interfere with the slow inactivation of INaP . Our data indicate that INaP can be targeted by the rich cholinergic period, neurons usually displayed a variable degree of INaP runup. After that period, control recordings (n Å5) showed that INaP reinnervation of the neocortex. Because INaP is activated in the subthreshold voltage range, cholinergic inhibition of this current would mained stable for the time of experimentation (10–15 min). If not stated otherwise, holding potential was 070 mV. The bath solution be particularly suited to modulate the electrical behavior of neocortical pyramidal cells below and near firing threshold. contained (in mM) 130 NaCl, 3 KCl, 1.6 CaCl2 , 0.4 CdCl2 , 2 MgCl2 , 25 HEPES/NaHEPES, and 10 D-glucose (pH 7.4). The pipette solution contained (in mM) 110 Cs-gluconate, 3 MgCl2 , 5 ethylene glycol-bis(b-aminoethyl ether)-N,N,N*,N *-tetraacetic I N T R O D U C T I O N acid, 5 HEPES, 2 Tris-ATP, 0.3 Tris-GTP, 15 phosphocreatine, Activation of muscarinic receptors exerts a wide spectrum and 0.1 leupeptin (pH 7.25, adjusted with NaOH). When filled with pipette solution, electrode resistances were 4–6 MV in the of actions in neocortical neurons, including modulation of bath and 15–25 MV in the whole cell configuration before series K currents, Ca currents, and a nonselective cation current resistance compensation (70–75%). Drugs were bath applied by (Haj-Dahmane and Andrade 1996; McCormick 1993). In means of a multiple-inlet system allowing complete bath exchange the present study, we investigated whether muscarinic recepwithin Ç15 s. Carbachol, atropine, and mecamylamine were all tor stimulation also would affect the persistent Na current purchased from Sigma (Deisenhofen, Germany). Statistics are pre(INaP) of neocortical neurons, a functionally important ion sented as means { SE. Statistical analyses ( t-test and analysis of conductance in the subthreshold voltage range (Crill 1996). variance) were done with the use of Graphpad Prism 2.0. It is firmly established that Na currents can be modulated by protein kinase Aand C-mediated phosphorylation of the