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1. 1. Radioligand binding and 45Ca2+ uptake measurements quantitated ion channel numbers and properties in brain membranes from Fisher 344 rats at 6, 12, 18 and 30 months of age. 2. 2. Decreases in 1,4-dihydropyridine density occurred in striatum, hippocampus and cortex with a decreased affinity. 3. 3. Decreases in w-conotoxin binding occurred in hippocampus and striatum with an increase in affinity. 4. 4. K+ depolarization-mediated 45Ca2+ uptake decreased only in striatum at 18 months. 5. 5. Decreases in glibenclamide binding occurred in cortex and cerebellum at 12–30 months. 6. 6. No changes in 1,4-dihydropyridine binding occurred with age in heart, but glibenclamide binding density was significantly decreased at 30 months.

The acute inhibitory actions of alcohol on K(+)-stimulated 45Ca2+ uptake into synaptosomes shows regional variation in sensitivity throughout the brain, suggesting the possibility of a selective action on a specific Ca2+ channel subtype. This was examined by comparing the effects of a homologous series of aliphatic alcohols on synaptosomal Ca2+ channels with their actions on K(+)-stimulated Ca2+ channels in guinea-pig intestinal longitudinal muscle, which have been demonstrated to be of the L-type. K(+)-stimulated contraction of and [3H]nitrendipine binding to smooth muscle were both inhibited by the alcohols at similar concentrations, with the potency increasing with chain length. In synaptosomes, however, K(+)-stimulated 45Ca2+ uptake was 5-30 times more sensitive to the inhibitory actions of alcohol than were [3H]nitrendipine and [125I]omega-conotoxin binding. These observations suggest that K(+)-stimulated 45Ca2+ uptake is mediated by a non-L non-N type channel which is more sensitive to the acute effects of alcohols. This is supported by the observation that K(+)-stimulated 45Ca2+ uptake which is insensitive to L- and N-channel antagonists was inhibited by funnel web spider venom.

Administration of 3,3'-iminodipropionitrile (IDPN) (1 g/kg, i.p. for 3 days) in mice leads to the development of a characteristic syndrome consisting of lateral and vertical head and neck movements, hyperactivity, random circling, increased locomotor activity, and increased startle response. Nifedipine, verapamil, and diltiazem (10 mg/kg) inhibited significantly the symptoms of IDPN-induced dyskinesia. However, there was no change in the affinity (KD) or the density of PN 200-110 binding sites (Bmax) in whole brains of IDPN-treated mice. Similarly, the K(+)-depolarization-dependent Ca2+ uptake in synaptosomes from whole brain, cortex, or striatum was not altered following IDPN treatment. However, IDPN caused a significant increase in the Bmax value (from 157 +/- 7 fmol/mg to 237 +/- 31 fmol/mg in control and treated groups, respectively) of PN 200-110 binding to the striatum without change of KD value (38 +/- 4.7 pM versus 33 +/- 1.6 pM). IDPN also caused a slight but significant decrease in the KD value (from 68 +/- 10.1 pM to 45 +/- 4.5 pM in control and treated groups, respectively), without significant change of Bmax value (563 +/- 51 fmol/mg versus 485 +/- 41 fmol/mg) of PN 200-110 binding to the cortex. IDPN did not alter omega-conotoxin binding in whole brain, striatum, or cortex. The behavioral effects of chronic IDPN treatment as inhibited by L-type calcium channel antagonists and this may be associated with the observed increase in striatal L-type calcium channels.

Publisher Summary Drugs that regulate Ca 2+ influx via voltage-gated Ca 2+ channels are called calcium antagonists or calcium-channel blockers. Phenylalkylamines, benzothiazepines, and the 1,4-dihydropyridines (DHPs) are drugs that bind to distinct but allosterically coupled receptors on the channel protein. DHPs bind to the channel with highest affinity and specificity. Calcium-channel antagonists are unique drugs; they have made major contributions to clinical medicine and the basic science of calcium-channel proteins. Because of the multiple roles of calcium ions in cell function, communication, and biochemical regulation, the control of calcium entry by calcium-channel antagonists has given therapeutic tools for a wide variety of clinical disorders. The high degree of selectivity and great sensitivity of calcium-channel antagonists for the L-type channel allow the cloning and molecular fingerprinting of the channel protein. Calcium-channel antagonists, in general, and the DHP derivatives, in particular, regulate calcium influx by modulating channel gating. This chapter presents a method to explain the voltage-dependent modulation of L-type calcium-channel activity by DHP derivatives. It discusses DHP modulation of recombinant channel activity.