Voltage-dependent Calcium Channel Abnormalities in Hippocampal CA3 Neurons of Spontaneously Epileptic Rats

In response to light, the mouse retinal pigment epithelium (RPE) generates a series of slow changes in potential that are referred to as the c-wave, fast oscillation (FO), and light peak (LP) of the electroretinogram (ERG). The LP is generated by a depolarization of the basolateral RPE plasma membrane by the activation of a calcium-sensitive chloride conductance. We have previously shown that the LP is reduced in both mice and rats by nimodipine, which blocks voltage-dependent calcium channels (VDCCs) and is abnormal in lethargic mice, carrying a null mutation in the calcium channel β4 subunit. To define the α1 subunit involved in this process, we examined mice lacking CaV1.3. In comparison with wild-type (WT) control littermates, LPs were reduced in CaV1.3−/− mice. This pattern matched closely with that previously noted in lethargic mice, confirming a role for VDCCs in regulating the signaling pathway that culminates in LP generation. These abnormalities do not reflect a defect in rod photoreceptor activity, which provides the input to the RPE to generate the c-wave, FO, and LP, because ERG a-waves were comparable in WT and CaV1.3−/− littermates. Our results identify CaV1.3 as the principal pore-forming subunit of VDCCs involved in stimulating the ERG LP.

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Altered Regulation of Potassium and Calcium Channels by GABAB and Adenosine Receptors in Hippocampal Neurons From Mice Lacking Gαo

Journal of Neurophysiology ◽

10.1152/jn.2000.83.2.1010 ◽

2000 ◽

Vol 83 (2) ◽

pp. 1010-1018 ◽

Cited By ~ 33

Author(s):

Gabriela J. Greif ◽

Deborah L. Sodickson ◽

Bruce P. Bean ◽

Eva J. Neer ◽

Ulrike Mende

Keyword(s):

Time Constant ◽

Hippocampal Neurons ◽

Ionic Currents ◽

Absolute Requirement ◽

Voltage Dependent ◽

Hippocampal Ca3 ◽

Ca3 Neurons ◽

Inwardly Rectifying ◽

G Protein Coupled

To examine the role of Go in modulation of ion channels by neurotransmitter receptors, we characterized modulation of ionic currents in hippocampal CA3 neurons from mice lacking both isoforms of Gαo. In CA3 neurons from Gαo −/− mice, 2-chloro-adenosine and the GABAB-receptor agonist baclofen activated inwardly rectifying K+ currents and inhibited voltage-dependent Ca2+ currents just as effectively as in Gαo +/+ littermates. However, the kinetics of transmitter action were dramatically altered in Gαo −/− mice in that recovery on washout of agonist was much slower. For example, recovery from 2-chloro-adenosine inhibition of calcium current was more than fourfold slower in neurons from Gαo −/− mice [time constant of 12.0 ± 0.8 (SE) s] than in neurons from Gαo +/+ mice (time constant of 2.6 ± 0.2 s). Recovery from baclofen effects was affected similarly. In neurons from control mice, effects of both baclofen and 2-chloro-adenosine on Ca2+ currents and K+currents were abolished by brief exposure to external N-ethyl-maleimide (NEM). In neurons lacking Gαo, some inhibition of Ca2+ currents by baclofen remained after NEM treatment, whereas baclofen activation of K+ currents and both effects of 2-chloro-adenosine were abolished. These results show that modulation of Ca2+ and K+ currents by G protein-coupled receptors in hippocampal neurons does not have an absolute requirement for Gαo. However, modulation is changed in the absence of Gαo in having much slower recovery kinetics. A likely possibility is that the very abundant Gαo is normally used but, when absent, can readily be replaced by G proteins with different properties.

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