Relationship between Muller cell responses, a local transretinal potential, and potassium flux

Abstract

1. In the Necturus retina, light-evoked field potentials, Müller (glial) cell responses, and extracellular potassium ion concentration ([K+]0) were recorded and found to exhibit the three-way correlation characteristic of these variables elsewhere in the nervous system. 2. Müller cell responses to a flashed spot or annulus consist primarily of slow depolarizations at both light onset and offset. The responses are maximum to 0.5-mm-diameter spots and decrease with larger diameters. Responses to stimulus intensity and flicker were also used to characterize Müller cell behavior. 3. In response to long-duration stimuli, the initial Müller cell depolarization is followed by a very slow hyperpolarization, which is likely the origin of slow PIII. 4. A new extracellular potential is described, the M-wave, the basic properties of which suggest that it is generated by Müller cells. Moreover, the M-wave and Müller cells show remarkably similar behavior to a wide variety of stimulus parameters. 5. In the proximal retina, [K+]0 increases at both light onset and offset with a time course similar to that of Müller cell depolarizing responses. This K+ increase also behaves similarly to the Müller cell depolarization in response to changes in stimulus parameters. 6. It is concluded that light stimulation leads to an increase in [K+]0 in the proximal retina and that this increase depolarizes Müller cells whose associated currents, in turn, generate the M-wave.

ERG Components of Negative Polarity from the Inner Retina and the Optic Nerve Response

“…M-wave: A local ERG component of negative polarity in the inner retina is the M-wave, first recorded and analyzed by Karwoski and Proenza [19] in the amphibian retina. It has been attributed mainly to changes in extracellular concentration of potassium ([K + ] o ) as caused by depolarization of the glial Mu¨ller cells [42].…”

Glial and neuronal dysfunction in streptozotocin-induced diabetic rats

“…It is these potassium channels that are involved in the buffering of extracellular potassium build-up that occurs following light activation. Specifically, the potassium buffering activity that follows the lightinduced cessation of the dark-current (the fast-P3 component) is thought to generate the slow-P3 component of the ERG [25]. This pharmacological approach allows us to expose the slow-P3 component which, under normal conditions, occurs with a similar time course to the corneal positive bipolar cell driven P2, such that the interaction between these generators produces the ERG b-wave.…”

Transient adaptation and sensitization in the retina of Necturus.

“…2, the standard stimulus sequence is reproduced, and field potential responses recorded in the proximal retina are displayed above it. To the small (0.25-mm) stimulus, the initial, negative-going, transient responses, best developed at light onset, are the proximal negative response (PNR) (Burkhardt, 1970;Proenza and Burkhardt, 1973), and the slower, negative-going components are the M-wave (Karwoski and Proenza, 1977). The specific relationships between responses (i.e., A > B = RD; D > E = TRE) can be more readily perceived in the bottom half of Fig.…”

“…The responses of 18 Mfiller cells, identified by the criteria of Miller and Dowling (1970) and Karwoski andProenza (1977 and1980) were also tested.…”

“…On the other hand, with regard to repetitive stimulation in which large and small spot sequences are alternated, it is found that the first small spot response after the large spot sequence is larger than the small spot responses that preceded the large spot sequence (Kaneko and Hashimoto, 1969;Proenza and Burkhardt, 1973;Karwoski and Proenza, 1977). This transient response enhancement is notable because it cannot have a photopigment origin because the same amount of light strikes the photoreceptors under the test spot when the large or small spots are presented.…”