Functional ionotropic glutamate receptors on peripheral axons and myelin.

Introduction: Neurotransmitter-dependent signaling is traditionally restricted to axon terminals. However, receptors are present on myelinating glia, suggesting that chemical transmission may also occur along axons.

Methods: Confocal microscopy and Ca(2+) -imaging using an axonally expressed FRET-based reporter was used to measure Ca(2+) changes and morphological alterations in myelin in response to stimulation of glutamate receptors.

Calcium-activated chloride channels in müller cells acutely isolated from tiger salamander retina.

Ca(2+)-activated chloride channels were identified with whole-cell patch-clamp recording techniques in salamander retinal Müller cells. Cl(Ca) channels were activated by membrane depolarizations that elicited Ca2+ influx or the application of the Ca2+ ionophore, ionomycin. The Ca channel blocker, Cd2+, abolished the Cl(Ca) channel tail currents.

High-voltage-activated calcium channels in Muller cells acutely isolated from tiger salamander retina.

Muller cells mediate retinal function by stabilizing the ionic environment and signal glial network activity via calcium waves. Using whole-cell patch clamp recording, we describe a high-voltage-activated, slowly inactivating Ca channel current in isolated salamander Muller cells that has unusual pharmacological properties. The Ca channel current has an activation midpoint of approximately -8 mV and an inactivation midpoint of approximately -26 mV in 10 mM Ba2+.

Carbenoxolone inhibition of voltage-gated Ca channels and synaptic transmission in the retina.

We show that carbenoxolone, a drug used to block hemichannels in the retina to test the ephaptic model of horizontal cell inhibitory feedback, has strong inhibitory effects on voltage-gated Ca channels. Carbenoxolone (100 microM) reduced photoreceptor-to-horizontal cell synaptic transmission by 92%. Applied to patch-clamped, isolated cone photoreceptors, carbenoxolone inhibited Ca channels with an EC(50) of 48 microM.