Membrane Biochemistry and Biophysics NeuroReport 0959-4965 # Lippincott Williams & Wilkins Facilitation of miniature GABAergic currents by chlorpromazine in cultured rat hippocampal cells Jerzy W. Mozrzymas, 1,2 Andrea Barberis 1 and Enrico Cherubini 1,CA 1 Neuroscience Program and Istituto Nazionale Fisica della Materia (INFM) Unit, International School for Advanced Studies (SISSA), via Beirut 2- 4, 34014 Trieste, Italy; 2 Department of Biophysics, Wroclaw University of Medicine, ul. Chalubinskiego 10, 50-368 Wroclaw, Poland CA Corresponding Author THE whole cell con®guration of the patch clamp tech- nique was used to study the effects of chlorpromazine (CPZ), a widely used antipsychotic drug, on miniature GABA A -mediated synaptic currents (mIPSCs) in hippo- campal cells in culture. CPZ (10±30 ìM) induced a clear dose-dependent increase of mIPSCs frequency that was associated with a decrease in amplitude and with an acceleration of their decay kinetics. When applied in a calcium-free medium, CPZ was less effective in enhan- cing mIPSCs frequency, suggesting that this effect was partially calcium dependent. While a low (10 ìM) CPZ concentration induced a 2-fold increase in the total charge transfer a higher (30 ìM) dose of this drug produced no changes, indicating that the presynaptic effect was counterbalanced by the postsynaptic one. NeuroReport 10:2251±2254 # 1999 Lippincott Williams & Wilkins. Key words: CPZ; GABA release; Hippocampal cells in culture; mIPSCs amplitude; mIPSCs frequency Introduction Phenothiazines (PTZs) are commonly used in the treatment of psychiatric disorders such as schizo- phrenia and depression. The therapeutic action of PTZs is attributed to the blockade of dopamine receptors [1,2]. However, it is known that PTZs interfere with various ligand- and voltage-activated channels [3±12]. In particular, PTZs block in a non- competitive manner the responses evoked by exo- genous application of GABA [7] and reduce the amplitude of inhibitory postsynaptic currents (IPSCs) [13]. In a recent study, we have demon- strated that chlorpromazine, a widely used PTZ, reduces the amplitude and accelerates the decay of miniature GABAergic currents (mIPSCs) in rat hippocampal cells in culture [14]. Moreover, using a fast perfusion system to mimic the time course of synaptic currents and to explore the mechanism of CPZ action, we have shown that these effects have a postsynaptic origin and are due to a decrease in binding and an increase in unbinding rate of GABA A receptors [14]. In the present study we examined the presynaptic action of CPZ on inhibitory synaptic transmission in cultured hippocampal cells. We report that CPZ strongly increases the frequency of mIPSCs in a dose dependent manner and that this effect partially depends on the presence of extracellular calcium. Materials and Methods Cell cultures of hippocampal neurons were prepared as described previously [15] and experiments were performed on cells between 5 and 12 days in culture. Currents were recorded in the whole-cell con®gura- tion of the patch-clamp technique using the EPC-7 ampli®er (List Medical, Darmstadt, Germany) at a holding potential of 70 mV. The intrapipette solu- tion contained (in mM): CsCl 137, CaCl 2 1, MgCl 2 2, 1,2-bis(2-aminophenoxy)ethane-n,n,n9-tetraacetic acid (BAPTA) 11, ATP 2, HEPES 10 (pH 7.2 with CsOH). The composition of the external solution was (in mM): NaCl 137, KCl 5, CaCl 2 2, MgCl 2 1, glucose 20, HEPES 10 (pH 7.4 with NaOH). The calcium-free solution contained 1 mM EGTA and the osmolarity was adjusted to that of the normal external solution by changing the glucose concentra- tion. mIPSCs were recorded in the presence of tetrodotoxin (TTX, 1 ìM) and kynurenic acid (1 mM) to block fast sodium spikes and glutama- tergic excitatory postsynaptic events. All experi- ments were performed at room temperature (22± 248C). NeuroReport 10, 2251±2254 (1999) Vol 10 No 11 2 August 1999 2251