L-type calcium channels in the axon terminal of mouse bipolar cells

Abstract

Two types of calcium current (I(Ca)) have been identified in the bipolar cell of the mouse retina: a transient (T-) type current and a long lasting (L-) type current. It has been suggested that the former is present in the soma and the latter in the axon terminal. To establish the cellular localization of the two types of I(Ca), bipolar cells of the mouse retina was studied electrophysiologically in a slice preparation, and immunocytochemically by staining specific calcium channels in isolated cells. The dihydropyridine-sensitive L-type I(Ca) was recorded in the axon terminal, and the T-type current was recorded in the somatic region. Strong immunoreactivity to a polyclonal antibody against the L-type calcium channel was found in the axon terminal. These observations suggest that the L-type I(Ca) is generated at the axon terminal and contributes to the transmission of sustained depolarization.

Imaging of Ca2+Dynamics Within the Presynaptic Terminals of Salamander Rod Photoreceptors

“…Use of different Ca 2ϩ channels (different subtypes, isoforms, or splice variants of the same isoform) with distinct properties within the terminal and somatic membranes could confer a degree of separation between voltage control of transmitter release from the terminal and other functions such as signal forwarding through the soma and regulation of gene expression in the nucleus. Compartmentalization of L-type and T-type channels was previously reported for both isolated and intact retinal mouse bipolar cells (de la Villa et al 1998;Satoh et al 1998). L-type currents were previously reported to shape the voltage response of depolarizing bipolar cells of goldfish (Burrone and Lagnado 1997).…”

Presynaptic Localization and Possible Function of Calcium-Activated Chloride Channel Anoctamin 1 in the Mammalian Retina

“…5A and B). This inward current was identified as L-type Ca 2+ current (I Ca ), which was described previously in rod bipolar cells [30], [31], because (1) potassium currents and h-current were suppressed by tetraethylammonium chloride (TEA) and CsCl; (2) it was detectable at depolarizing potentials between about −60 mV and +40 mV and had a peak amplitude of 20±4 pA at a voltage of about −30 mV; and (3) it was sensitive to nifedipine, which is L-type Ca 2+ channel antagonist (Fig. S2).…”

Synaptic release at mammalian bipolar cell terminals

“…Mutations in Cav1.4 channels, which are also present on rod photoreceptor terminals (Morgans et al, 2005), are associated with incomplete X-linked congenital stationary night blindness in humans (CSNB2) (Bech-Hansen et al, 1998; Strom et al, 1998). Mouse bipolar cells have also been reported to express a transient T-type I Ca (Kaneko et al, 1989; Kaneko et al, 1991) but there is evidence to suggest that these channels are not present in the synaptic endings (Satoh et al, 1998). Thus, in contrast to the rat, the T-type calcium channel may not be positioned in the mouse rod bipolar cell to drive exocytosis.…”