Role of voltage-gated L-type Ca2+ channel isoforms for brain function

Voltage-gated LTCCs (L-type Ca2+ channels) are established drug targets for the treatment of cardiovascular diseases. LTCCs are also expressed outside the cardiovascular system. In the brain, LTCCs control synaptic plasticity in neurons, and DHP (dihydropyridine) LTCC blockers such as nifedipine modulate brain function (such as fear memory extinction and depression-like behaviour). Voltage-sensitive Ca2+ channels Cav1.2 and Cav1.3 are the predominant brain LTCCs. As DHPs and other classes of organic LTCC blockers inhibit both isoforms, their pharmacological distinction is impossible and their individual contributions to defined brain functions remain largely unknown. Here, we summarize our recent experiments with two genetically modified mouse strains, which we generated to explore the individual biophysical features of Cav1.2 and Cav1.3 LTCCs and to determine their relative contributions to various physiological peripheral and neuronal functions. The results described here also allow predictions about the pharmacotherapeutic potential of isoform-selective LTCC modulators.

Brain activation pattern induced by stimulation of L-type Ca2+-channels: Contribution of CaV1.3 and CaV1.2 isoforms

Ca(V)1.2 and Ca(V)1.3, are the main dihydropyridine-sensitive L-type calcium channel isoforms in the brain. To reveal the contribution of each isoform to the neuronal activation pattern elicited by the dihydropyridine L-type calcium channel activator BayK 8644, we utilized Fos expression as a marker of neuronal activation in mutant mice (Ca(V)1.2(DHP-/-) mice) expressing dihydropyridine-insensitive Ca(V)1.2 L-type calcium channels. BayK 8644-treated wildtype mice displayed intense and widespread Fos expression throughout the neuroaxis in 77 of 80 brain regions quantified. The Fos response in Ca(V)1.2(DHP-/-) mice was greatly attenuated or absent in most of these areas, suggesting that a major part of the widespread Fos induction including most cortical areas was mediated by Ca(V)1.2 L-type calcium channels. BayK 8644-induced Fos expression in Ca(V)1.2(DHP-/-) mice indicating predominantly Ca(V)1.3 L-type calcium channel-mediated activation was noted in more restricted neuronal populations (20 of 80), in particular in the central amygdala, the bed nucleus of the stria terminalis, paraventricular hypothalamic nucleus, lateral preoptic area, locus coeruleus, lateral parabrachial nucleus, central nucleus of the inferior colliculus, and nucleus of the solitary tract. Our data indicate that selective stimulation of other than Ca(V)1.2 L-type calcium channels, mostly Ca(V)1.3, causes neuronal activation in a specific set of mainly limbic, hypothalamic and brainstem areas, which are associated with functions including integration of emotion-related behavior. Hence, selective modulation of Ca(V)1.3 L-type calcium channels could represent a novel (pharmacotherapeutic) tool to influence these CNS functions.