Second messengers involved in genetic regulation of the number of calcium channels in bovine adrenal chromaffin cells in culture

Role of the GTP-binding protein G(o) in the suppressant effect of ethanol on voltage-activated calcium channels of murine sensory neurons

Whole-cell and single-channel recording techniques were used to investigate the acute, in vitro effects of ethanol on the function of voltage-activated Ca2+ channels in cultured neurons derived from dorsal root ganglia (DRG) of embryonic mice. Although 5.4 mM ethanol produced a sustained increase of the amplitude of the whole-cell Ca2+ current (ICa), 43.2 mM ethanol had a time-dependent biphasic effect. That is, within 0.5 min of exposure to 43.2 mM ethanol, the maximal amplitude of ICa initially increased before declining to a new steady-state value. As anticipated, the facilitatory and inhibitory effects of ethanol on ICa were associated with an increase and decrease, respectively, in the probability of single-channel open events. Pretreatment of DRG with 200 ng/ml of pertussis toxin abolished the inhibitory, but not the facilitatory, effect of 43.2 mM ethanol on ICa. Pretreatment with pertussis toxin also prevented the reduction of the probability of single-channel opening caused by 43.2 mM ethanol. Similarly, dialysis of neurons with polyclonal antibodies against the alpha-subunit of G(o) but not Gs, abolished the inhibitory effect of 43.2 mM ethanol on ICa. These data demonstrate concentration- and time-dependent biphasic effects of ethanol on the activity of Ca2+ channels. The inhibitory effect of ethanol requires activation of the alpha-subunit of G(o), which then decreases the probability of Ca2+ channel opening.

Smithkline Beecham Prize for Young Psychopharmacologists: A review of the relationship between calcium channels and psychiatric disorders

The symptoms and etiology of most major psychiatric disorders probably represent an underlying disturbance of neurotransmitter function. Understanding the mechanisms which control neurotransmitter function, and in particular neurotransmitter release, is therefore of considerable importance in determining the appropriate pharmacological treatment for these disorders. Calcium entry into neurons triggers the release of a wide range of neurotransmitters and recently our understanding of the mechanisms which control neuronal calcium entry has increased considerably. Neuronal calcium entry occurs through either voltage-sensitive or receptor-operated calcium channels. This article reviews the different subtypes of calcium channel, with particular reference to their structure; drugs which act upon them; and the possible function of the subtypes identified to date. In addition, it reviews the potential role of calcium channel antagonists in the treatment of a wide range of psychiatric disorders, and concludes that these drugs may have an increasing therapeutic role particularly in the treatment of drug dependence, mood disorders and Alzheimer's disease.

Chronic dihydropyridine treatment can reverse the behavioural consequences of and prevent adaptations to, chronic ethanol treatment

1. Chronic treatment with the dihydropyridine calcium channel antagonist, nitrendipine, given concurrently with ethanol, prevented the ethanol withdrawal syndrome in mice, even though the chronic nitrendipine treatment was stopped 24 h or 48 h before the withdrawal testing. 2. This effect was seen in two strains of mice with different methods of ethanol administration. Nitrendipine was effective when given for two weeks but not after only two days' treatment. 3. Two other dihydropyridine calcium antagonists, nimodipine and PN 200-110, given chronically with ethanol, also prevented the withdrawal syndrome. The tests were again made 24 h after the last administration of dihydropyridine. 4. The chronic nitrendipine treatment also prevented the rise in the number of central dihydropyridine binding sites that occurs on chronic ethanol administration. 5. Chronic administration of nitrendipine alone did not cause any withdrawal behaviour. 6. Chronic nitrendipine treatment did not affect the seizure threshold to bicuculline in mice that were not given ethanol. 7. Whole brain concentration measurements showed that the effects were not due to residual nitrendipine in the CNS at the time of withdrawal testing or to differences in central ethanol concentrations during the treatment. 8. It is suggested that the results provide evidence for a functional role for dihydropyridine-sensitive calcium channels in ethanol dependence.

Nitrendipine, given during drinking, decreases the electrophysiological changes in the isolated hippocampal slice, seen during ethanol withdrawal

1. Extracellular recordings were made from mouse isolated hippocampal slices prepared after chronic treatment in vivo with either ethanol or ethanol plus the dihydropyridine calcium channel antagonist, nitrendipine. 2. The withdrawal of ethanol caused a variety of changes in the field potentials, as previously reported, including decreases in the thresholds for eliciting single and multiple population spikes, increases in paired pulse potentiation and shifts to the left of the input/output curves. 3. The addition of nitrendipine to the drinking mixture in the chronic ethanol treatment significantly decreased all the changes in the field potentials that were seen after ethanol withdrawal. 4. Addition of nitrendipine to the perfusion medium also decreased the signs of hyperexcitability seen in the hippocampal slices during ethanol withdrawal. 5. The results provide further evidence that neuronal calcium channels may be involved in ethanol dependence and that the adaptive changes caused by chronic ethanol treatment can be modulated by alterations at dihydropyridine-sensitive sites.

The role of neuronal calcium channels in dependence on ethanol and other sedatives/hypnotics

This review discusses the importance of neuronal calcium currents in dependence on ethanol, barbiturates, benzodiazepines and opiates. The main sections describe the actions of ethanol on control of intracellular calcium and on calcium and calcium-dependent conductance mechanisms. In particular, the effects of both acute and chronic ethanol treatment on dihydropyridine-sensitive, voltage-dependent, calcium channels are described. The later sections cover the effects of barbiturates, benzodiazepines and opiates on these systems. The conclusions suggest that dihydropyridine calcium channel antagonists may offer a new therapeutic approach to the treatment of ethanol and opiate dependence.