Signs of physical dependence as a consequence of long-term drug use and a moderate abuse liability limit benzodiazepine clinical usefulness. Growing evidence suggests a role for voltage-gated calcium channel (VGCC) regulation in mediating a range of chronic drug effects from drug withdrawal phenomena to dependence on a variety of drugs of abuse. High voltageactivated (HVA) calcium currents were measured in whole-cell recordings from acutely isolated hippocampal CA1 neurons after a 1-week flurazepam (FZP) treatment that results in withdrawal-anxiety. An ϳ1.8-fold increase in Ca 2ϩ current density was detected immediately after and up to 2 days but not 3 or 4 days after drug withdrawal. Current density was unchanged after acute desalkyl-FZP treatment. A significant negative shift of the half-maximal potential of activation of HVA currents was also observed but steady-state inactivation remained unchanged. FZP and diazepam showed use-and concentration-

Benzodiazepines (BDZs) depress neuronal excitability via positive allosteric modulation of inhibitory GABA A receptors (GABA A R). BDZs and other positive GABA A R modulators, including barbiturates, ethanol, and neurosteroids, can also inhibit L-type voltage-gated calcium channels (L-VGCCs), which could contribute to reduced neuronal excitability. Because neuronal L-VGCC function is up-regulated after long-term GABA A R modulator exposure, an interaction with L-VGCCs may also play a role in physical dependence. The current studies assessed the effects of BDZs (diazepam, flurazepam, and desalkylflurazepam), allopregnanolone, pentobarbital, and ethanol on whole-cell Ba 2ϩ currents through recombinant neuronal Ca v 1.2 and Ca v 1.3 L-VGCCs expressed with ␤ 3 and ␣ 2 ␦-1 in HEK293T cells. Allopregnanolone was the most potent inhibitor (IC 50 , ϳ10 M), followed by BDZs (IC 50 , ϳ50 M), pentobarbital (IC 50 , 0.3-1 mM), and ethanol (IC 50 , ϳ300 mM). Ca v 1.3 channels were less sensitive to pentobarbital inhibition than Ca v 1.2 channels, similar to dihydropyridine (DHP) L-VGCC antagonists. All GABA A R modulators induced a negative shift in the steady-state inactivation curve of Ca v 1.3 channels, but only BDZs and pentobarbital induced a negative shift in Ca v 1.2 channel inactivation. Mutation of the high-affinity DHP binding site (T1039Y and Q1043M) in Ca v 1.2 channels reduced pentobarbital potency. Despite the structural similarity between benzothiazepines and BDZs, mutation of an amino acid important for diltiazem potency (I1150A) did not affect diazepam potency. Although L-VGCC inhibition by BDZs occurred at concentrations that are possibly too high to be clinically relevant and is not likely to play a role in the up-regulation of L-VGCCs during long-term treatment, pentobarbital and ethanol inhibited L-VGCCs at clinically relevant concentrations.

No abstract

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see http://www.jneurosci.org/misc/ifa_features.shtml.