Epilepsy Research 43 (2001) 211 – 226 Epilepsy-induced decrease of L-type Ca 2 + channel activity and coordinate regulation of subunit mRNA in single neurons of rat hippocampal ‘zipper’ slices Eric M. Blalock 1 a, *, Kuey-Chu Chen a,1 , Thomas C. Vanaman b , Philip W. Landfield a , John T. Slevin a,c a Department of Pharmacology, College of Medicine, Uniersity of Kentucky, MS -310 UKMC, Lexington, KY 40536, USA b Department of Biochemistry, College of Medicine, Uniersity of Kentucky, Lexington, KY 40536, USA c Department of Neurology, Lexington Veterans Administration, College of Medicine, Uniersity of Kentucky, Lexington, KY 40536, USA Received 8 June 2000; received in revised form 6 September 2000; accepted 16 October 2000 Abstract L-type voltage-sensitive Ca 2 + channels (VSCCs) preferentially modulate several neuronal processes that are thought to be important in epileptogenesis, including the slow afterhyperpolarization (AHP), LTP, and trophic factor gene expression. However, little is yet known about the roles of L-type VSCCs in the epileptogenic process. Here, we used cell-attached patch recording techniques and single cell mRNA analyses to study L-type VSCCs in CA1 neurons from partially dissociated (zipper) hippocampal slices from entorhinally-kindled rats. L-type Ca 2 + -channel activity was reduced by 50% at 1.5 – 3 months after kindling. Following recording, the same single neurons were extracted and collected for mRNA analysis using a recently developed method that does not amputate major dendritic processes. Therefore, neurons contained essentially full complements of mRNA. For each collected neuron, mRNA contents for the L-type pore-forming  1D /Ca v 1.3-subunit and for calmodulin were then analyzed by semiquantitative kinetic RT-PCR. L-type  1D -subunit mRNA was correlated with L-type Ca 2 + -channel activity across single cells, whereas calmodulin mRNA was not. Thus, these results appear to provide the first direct evidence at the single channel and gene expression levels that chronic expression of an identified Ca 2 + -channel type is modulated by epileptiform activity. Moreover, the present data suggest the hypothesis that down regulation of  1D -gene expression by kindling may contribute to the long-term maintenance of epileptiform activity, possibly through reduced Ca 2 + -dependent AHP and/or altered expression of other relevant genes. © 2001 Elsevier Science B.V. All rights reserved. Keywords:  1D subunit; Kindling; Calmodulin; Reverse transcriptase-polymerase chain reaction; Seizures; Gene expression www.elsevier.com/locate/epilepsyres * Corresponding author. Tel.: +1-859-3236134; fax: +1-859-3231981. E-mail address: emblal@uky.edu (E.M. Blalock 1 ). 1 These authors contributed equally to the present work. 0920-1211/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0920-1211(00)00199-6