Generators of Pressure-Evoked Currents in Vertebrate Outer Retinal Neurons

Abstract

(1) Background: High-tension glaucoma damages the peripheral vision dominated by rods. How mechanosensitive channels (MSCs) in the outer retina mediate pressure responses is unclear. (2) Methods: Immunocytochemistry, patch clamp, and channel fluorescence were used to study MSCs in salamander photoreceptors. (3) Results: Immunoreactivity of transient receptor potential channel vanilloid 4 (TRPV4) was revealed in the outer plexiform layer, K+ channel TRAAK in the photoreceptor outer segment (OS), and TRPV2 in some rod OS disks. Pressure on the rod inner segment evoked sustained currents of three components: A) the inward current at <−50 mV (Ipi), sensitive to Co2+; B) leak outward current at ³−80 mV (Ipo), sensitive to intracellular Cs+ and ruthenium red; and C) cation current reversed at ~10 mV (Ipc). Hypotonicity induced slow currents like Ipc. Environmental pressure and light increased the FM 1-43-identified open MSCs in the OS membrane, while pressure on the OS with internal Cs+ closed a Ca2+-dependent current reversed at ~0 mV. Rod photocurrents were thermosensitive and affected by MSC blockers. (4) Conclusions: Rods possess depolarizing (TRPV) and hyperpolarizing (K+) MSCs, which mediate mutually compensating currents between −50 mV and 10 mV, serve as an electrical cushion to minimize the impact of ocular mechanical stress.

Mechanism of barotaxis in marine zooplankton

“…TRP channels can signal downstream of opsins in phototransduction cascades and have been postulated as the ultimate integrators of sensory stimuli (Liu and Montell 2015). Mechanosensitivity 2+ 2+ d1_unp has also recently been reported for vertebrate rods (Bocchero et al 2020), including the activation of these ciliary photoreceptors by pressure (Pang, Gao, and Wu 2021). The cellular and molecular mechanisms behind this sensitivity are still unclear, but TRP or Piezo channels were suggested to be involved (Bocchero et al 2020).…”

Transient Receptor Potential-Vanilloid (TRPV1-TRPV4) Channels in the Atlantic Salmon, Salmo salar. A Focus on the Pineal Gland and Melatonin Production

“…In a general manner, Atlantic salmon TRPV1-and TRPV4like proteins distributed as described in other vertebrate species [fish: (Sanchez-Ramos et al, 2012;Nisembaum et al, 2015); mouse: (Ryskamp et al, 2011;Lakk et al, 2018); Monkeys and human: (Gau et al, 2013;Sappington et al, 2015)]. Most of the studies dealing with TRPV1 and TRPV4 in the vertebrates' retina indicate a role in detecting variations in temperature, osmotic pressure, mechanical, volume and hydrostatic changes (linked to systemic changes in blood pressure, hydrostatic pressure from the CSF and intrinsic intraocular pressure), as well as in mediating the response to chemicals (lipids and endocannabinoids) (Alessandri-Haber et al, 2006;Ryskamp et al, 2011Ryskamp et al, , 2014Ye et al, 2012;Sappington et al, 2015;Toft-Bertelsen et al, 2019;Pang et al, 2021;Redmon et al, 2021). In the Atlantic salmon retina, TRPV1 and TRPV4 were expressed in some, but not all, photoreceptors, highlighting a heterogeneity among the photoreceptor cell types; this contrasts with the situation observed in the pineal gland of this same species, or the retina of the rainbow trout, in which all the ONL appeared to express TRPV1 and TRPV4.…”

Retinal Mechanical Sensation

“…BKs were reported in rods in goldfish [27] and salamander retinas [28][29][30]. They were expressed in the axon terminal [27], soma, and inner segment (IS) [28,31] of rods and associated with membrane hyperpolarization and glutamate release [29].…”

“…The I(KCa) was largely inhibited by 100 nM iberiotoxin, a BK blocker, and sensitive to tetraethylammonium (TEA) [29]. BK blocker iberiotoxin increases the light response of some rods [30]. BK may be activated by flupirtine [32].…”

“…BK may be activated by flupirtine [32]. Cones from the rabbit and salamander retina also express BK [30,33]. Studies from other tissues have revealed the mechanical sensitivity of BKs [34][35][36].…”