The electrical properties of rat Purkinje cells and synapses from granule cells were studied in dissociated cell cultures. To identify the cells we used an immunohistochemical method and recorded voltage-gated and synaptic currents with the patch-clamp technique (the whole-cell mode). Cultured Purkinje cells generated action potentials similar to those recorded from in vitro slices or in vivo preparations. Early Na, late Ca inward current, and K outward currents were distinguished by ion substitution under voltage clamp. We also recorded spontaneous synaptic currents in Purkinje cells cultured with granule cells. These synaptic currents reversed direction at the membrane potential of 2.5 mV, which was similar to currents induced by L-glutamate. Therefore, these are most likely excitatory synaptic currents from granule cells. Since these properties of Purkinje cells examined here are similar to those in situ, the cells in dissociated cell cultures offer a great opportunity to study biophysical properties of identified neurons in the central nervous system. Electrical properties of cultured neurons from various parts of the mammalian central nervous system (CNS) have been studied (1); however, there are several problems in such studies. The first problem is identification of a particular type of neuron in cell culture and the second is proof that the cells under investigation retain the properties of their physiological state. The third problem is to obtain stable electrical recordings from small neurons. Two recent technical advances overcome these three difficulties. Production of specific polyclonal and monoclonal antibodies allows the identification of several neurons in the mammalian CNS. With the patch (whole-cell) recording technique we can monitor electrical activities of cultured small cells and also control the intracellular ionic environment (2).The cerebellum is one of the best studied parts of the CNS (3, 4). Its neuronal circuit and development are well understood (3, 4), and several markers have already been found that specifically bind to Purkinje cells (5-7) and granule cells (8). Methods for culturing Purkinje cells (5) and granule cells (8-10) have also been established. In this study we applied the whole-cell patch-clamp technique to Purkinje cells in dissociated cell cultures and recorded various ionic currents.
MATERIALS AND METHODSPrimary Culture. Purkinje cells were cultured as reported (5). In short, cerebella were dissected from rat fetuses on approximately embryonic day 20 and freed of meninges. The cerebella were incubated at 20°C for 4 min in 1% trypsin/0.05% DNase solution, which contained 137 mM NaCl, 5 mM KCl, 7 mM Na2PO4, and 25 mM Hepes (pH 7.2). After three washings with Ca-and Mg-free Hanks' balanced salt solution the tissue was dissociated by triturating with firepolished Pasteur pipets in Ca-free Hanks' balanced salt solution containing 0.05% DNase and 12 mM MgSO4. The cell suspension was centrifuged at 180 x g at 40C and the pelleted cells were resuspended at a concen...