Gain-of-function nature of Cav1.4 L-type calcium channels alters firing properties of mouse retinal ganglion cells.
Proper function of Cav1.4 L-type calcium channels is crucial for neurotransmitter release in the retina. Our understanding about how different levels of Cav1.4 channel activity affect retinal function is still limited. In the gain-of-function mouse model Cav1.4-IT we expected a reduction in the photoreceptor dynamic range but still transmission toward retinal ganglion cells. A fraction of Cav1.4-IT ganglion cells responded to light stimulation in multielectrode array recordings from whole-mounted retinas, but showed a significantly delayed response onset. Another significant number of cells showed higher activity in darkness. In addition to structural remodeling observed at the first retinal synapse of Cav1.4-IT mice the functional data suggested a loss of contrast enhancement, a fundamental feature of our visual system. In fact, Cav1.4-IT mouse retinas showed a decline in spatial response and changes in their contrast sensitivity profile. Photoreceptor degeneration was obvious from the nodular structure of cone axons and enlarged pedicles which partly moved toward the outer nuclear layer. Loss of photoreceptors was also expressed as reduced expression of proteins involved in chemical and electrical transmission, as such metabotropic glutamate receptor mGluR6 and the gap junction protein Connexin 36. Such gross changes in retinal structure and function could also explain the diminished visual performance of CSNB2 patients. The expression pattern of the plasma-membrane calcium ATPase 1 which participates in the maintenance of the intracellular calcium homeostasis in photoreceptors was changed in Cav1.4-IT mice. This might be part of a protection mechanism against increased calcium influx, as this is suggested for Cav1.4-IT channels.
a Medical University Vienna, Center for Physiology and Pharmacology; Department of Neurophysiology and -pharmacology ; Vienna , Austria.
Dagmar
D
Knoflach
a Medical University Vienna, Center for Physiology and Pharmacology; Department of Neurophysiology and -pharmacology ; Vienna , Austria.
Klaus
K
Schicker
b University of Veterinary Medicine, Vetcore ; Vienna , Austria.
Martin
M
Glösmann
a Medical University Vienna, Center for Physiology and Pharmacology; Department of Neurophysiology and -pharmacology ; Vienna , Austria.|c University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology ; Innsbruck , Austria.
Alexandra
A
Koschak
D000200:Action Potentials; D000818:Animals; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D015350:Contrast Sensitivity; D015785:Eye Diseases, Hereditary / Q000235:genetics / Q000378:metabolism*; D040181:Genetic Diseases, X-Linked / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009216:Myopia / Q000235:genetics / Q000378:metabolism*; D009755:Night Blindness / Q000235:genetics / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000502:physiology; D000097004:Gap Junction delta-2 Protein
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D017630:Connexins; D000097004:Gap Junction delta-2 Protein; C480684:Cacna1f protein, mouse
L-type calcium channel; channelopathy; congenital stationary night blindness; contrast sensitivity; multielectrode array recording; type 2