Changes In Cav1 Research Articles

Hyperglycemia and downregulation of caveolin-1 enhance neuregulin-induced demyelination.

Neuregulins (NRGs) are growth factors which bind to Erb receptor tyrosine kinases that localize to Schwann cells (SCs). Although NRGs can promote cell survival, mitogenesis, and myelination in undifferentiated SCs, they also induce demyelination of myelinated co-cultures of SCs and dorsal root ganglion (DRG) neurons. We have shown previously that Erb B2 activity increased in premyelinating SCs in response to hyperglycemia, and that this correlated with the downregulation of the protein caveolin-1 (Cav-1). As myelinated SCs undergo substantial degeneration in diabetic neuropathy, we used myelinated SC/DRG neuron co-cultures to determine if hyperglycemia and changes in Cav-1 expression could enhance NRG-induced demyelination. In basal glucose, NRG1 caused a 2.4-fold increase in the number of damaged myelin segments. This damage reached 3.8-fold under hyperglycemic conditions, and was also associated with a robust decrease in the expression of Cav-1 and compact myelin proteins. The loss of Cav-1 and compact myelin proteins following hyperglycemia and NRG treatment was not due to neuronal loss, since the axons remained intact and there was no loss of PGP 9.5, an axonal marker protein. To examine if changes in Cav-1 were sufficient to alter the extent of NRG-induced demyelination, SC/DRG neurons co-cultures were infected with antisense or dominant-negative Cav-1(P132L) adenoviruses. Either antisense-mediated downregulation or mis-localization of endogenous Cav-1 by Cav-1(P132L) resulted in a 1.5- to 2.4-fold increase in NRG-induced degeneration compared to that present in control cultures. These data support that hyperglycemia and changes in Cav-1 are sufficient to sensitize myelinated SC/DRG co-cultures to NRG-induced demyelination.

Congenital Stationary Night Blindness Type 2 Mutations S229P, G369D, L1068P, and W1440X Alter Channel Gating or Functional Expression of Cav1.4 L-type Ca2+Channels

Mutations in the CACNA1F gene (voltage-dependent L-type calcium channel alpha1F subunit) encoding retinal Ca(v)1.4 L-type Ca2+ channels cause X-linked recessive congenital stationary night blindness type 2 (CSNB2). Many of them are predicted to yield nonfunctional channels. Complete loss of Ca(v)1.4 function is therefore regarded as a pathogenetic mechanism for the impaired signaling from photoreceptors to second-order retinal neurons. We investigated the functional consequences of CSNB2 missense mutations S229P, G369D, and L1068P and the C-terminal truncation mutant W1440X. After expression in Xenopus laevis oocytes or human embryonic kidney tsA-201 cells, inward Ca2+ current (I(Ca)) and inward Ba2+ current (I(Ba)) could be recorded from mutations G369D and L1068P. G369D shifted the half-maximal voltage for channel activation (V(0.5,act)) significantly to more negative potentials (>11 mV), slowed inactivation, and removed Ca2+-dependent inactivation. The L1068P mutant yielded currents only in the presence of the channel activator BayK8644. Currents (I(Ba)) inactivated faster than wild type (WT) and recovered more slowly from inactivation (I(Ba) and I(Ca)). No channel activity could be measured for mutants S229P and W1440X after oocyte expression. No W1440X alpha1 protein was detected after expression in tsA-201 cells, whereas S229P (as well as G369D and L1068P) alpha1 subunits were expressed at levels indistinguishable from WT (n = 3). Our data provide unequivocal evidence that CSNB2 missense mutations can induce severe changes in Ca(v)1.4 function, which may decrease (L1068P and S229P) or even increase (G369D) channel activity. The lower activation range of G369D can explain the reduced dynamic range of photoreceptor signaling. Moreover, we demonstrate that loss of channel function of one (L1068P) CSNB2 mutation can be rescued by a Ca2+ channel activator.

L-type Ca2+ channels mediate adaptation of extracellular signal-regulated kinase 1/2 phosphorylation in the ventral tegmental area after chronic amphetamine treatment.

L-type Ca2+ channels (LTCCs) play an important role in chronic psychostimulant-induced behaviors. However, the Ca2+ second messenger pathways activated by LTCCs after acute and recurrent psychostimulant administration that contribute to drug-induced molecular adaptations are poorly understood. Using a chronic amphetamine treatment paradigm in rats, we have examined the role of LTCCs in activating the mitogen-activated protein (MAP) kinase pathway in the ventral tegmental area (VTA), a primary target for the reinforcing properties of psychostimulants. Using immunoblot and immunohistochemical analyses, we find that in chronic saline-treated rats a challenge injection of amphetamine increases phosphorylation of MAP [extracellular signal-regulated kinase 1/2 (ERK1/2)] kinase in the VTA that is independent of LTCCs. However, in chronic amphetamine-treated rats there is no increase in amphetamine-mediated ERK1/2 phosphorylation unless LTCCs are blocked, in which case there is robust phosphorylation in VTA dopamine neurons. Examination of the expression of phosphatases reveals an increase in calcineurin [protein phosphatase 2B (PP2B)] and MAP kinase phosphatase-1 (MKP-1) in the VTA. Using in situ hybridization histochemistry and immunoblot analyses, we further examined the mRNA and protein expression of the LTCC subtypes Ca(v)1.2 and Ca(v)1.3 in VTA dopamine neurons in drug-naive animals and in rats after chronic amphetamine treatment. We found an increase in Ca(v)1.2 mRNA and protein levels, with no change in Ca(v)1.3. Together, our results suggest that one aspect of LTCC-induced changes in second messenger pathways after chronic amphetamine exposure involves activation of the MAP kinase phosphatase pathway by upregulation of Ca(v)1.2 in VTA dopaminergic neurons.

Neurological phenotype and synaptic function in mice lacking the Ca V1.3 α subunit of neuronal L-type voltage-dependent Ca 2+ channels

Neuronal L-type calcium channels have been implicated in pain perception and neuronal synaptic plasticity. To investigate this we have examined the effect of disrupting the gene encoding the Ca V1.3 (α1D) α subunit of L-type Ca 2+ channels on neurological function, acute nociceptive behavior, and hippocampal synaptic function in mice. Ca V1.3 α1 subunit knockout (Ca V1.3α1 −/−) mice had relatively normal neurological function with the exception of reduced auditory evoked behavioral responses and lower body weight. Baseline thermal and mechanical thresholds were unaltered in these animals. Ca V1.3α1 −/− mice were also examined for differences in N-methyl- d-aspartate (NMDA) receptor-dependent (100 Hz tetanization for 1 s) and NMDA receptor-independent (200 Hz in 100 μM DL-2-amino-5-phosphopentanoic acid) long-term potentiation within the CA1 region of the hippocampus. Both NMDA receptor-dependent and NMDA receptor-independent forms of long-term potentiation were expressed normally. Radioligand binding studies revealed that the density of (+)[ 3H]isradipine binding sites in brain homogenates was reduced by 20–25% in Ca V1.3α1 −/− mice, without any detectable change in Ca V1.2 (α1C) protein levels as detected using Western blot analysis. Taken together these data indicate that following loss of Ca V1.3α1 subunit expression there is sufficient residual activity of other Ca 2+ channel subtypes to support NMDA receptor-independent long-term potentiation and some forms of sensory behavior/function.