Biology subjects

Rosenbaum, T.

Publications and source records attributed to Rosenbaum, T..

6 recordsLinked to original sources

bioRxiv2023

Crucial role for Sodium Hydrogen Exchangers in SGLT2 inhibitor-induced arterial relaxations

1IntroductionSodium dependent glucose transporter 2 (SGLT2 or SLC5A2) inhibitors effectively lower blood glucose and are also approved treatments for heart failure independent of raised glucose. One component of the cardioprotective effect is reduced cardiac afterload but the mechanisms underlying peripheral relaxation are ill defined and variable. We speculated that SGLT2 inhibitors promoted arterial relaxation via the release of the potent vasodilator calcitonin gene-related peptide (CGRP) from sensory nerves independent of glucose transport. Experimental approachThe functional effects of SGLT2 inhibitors (dapagliflozin, empagliflozin, ertugliflozin) and the sodium/hydrogen exchanger 1 (NHE1) blocker cariporide were determined on pre-contracted mesenteric and renal arteries from male Wistar rats using Wire-Myography. SGLT2, NHE1, CGRP and TRPV1 expression in both arteries was determined by Western blot and immunohistochemistry. Kv7.4/5/KCNE4 and TRPV1 currents were measured in the presence and absence of dapagliflozin and empagliflozin. ResultsAll SGLT2 inhibitors produced a concentration dependent relaxation (1{micro}M-100{micro}M) of mesenteric arteries that was considerably greater than in renal arteries. Cariporide relaxed mesenteric arteries but not renal arteries. Immunohistochemistry with TRPV1 and CGRP antibodies revealed a dense innervation of sensory nerves in mesenteric arteries that was absent in renal arteries. Consistent with a greater sensory nerve component, the TRPV1 agonist capsaicin produced significantly greater relaxations in mesenteric arteries compared to renal arteries. Relaxations to dapagliflozin, empagliflozin and cariporide were attenuated by incubation with the CGRP receptor antagonist BIBN-4096, the Kv7 blocker linopirdine and the TRPV1 antagonist AMG-517 as well as by depletion of neuronal CGRP. Neither dapagliflozin nor empagliflozin directly activated heterologously expressed TRPV1 channels or Kv7 channels. Strikingly, only NHE1 colocalised with TRPV1 in sensory nerves, and cariporide pre-application prevented the relaxant response to SGLT2 inhibitors. ConclusionsSGLT2 inhibitors relax mesenteric arteries by a novel mechanism involving the release of CGRP from sensory nerves following inhibition of the Na+/H+ exchanger.

physiology↗

bioRxiv2023

Cation permeability and pore dynamics in TRPV1 ion channels

The Transient Receptor Vanilloid 1 (TRPV1) is a non-selective ion channel, which is activated by several chemical ligands and heat. We have previously shown that activation of TRPV1 by different ligands result in single-channel openings with different conductance, suggesting that the selectivity filter is highly dynamic. TRPV1 is weakly voltage-dependent, here we sought to explore whether the permeation of different monovalent ions could influence the voltage-dependence of this ion channel. By using single-channel recordings, we show that TRPV1 channels undergo rapid transitions to closed states that are directly connected to the open state, which may result from structural fluctuations of their selectivity filters. Moreover, we demonstrate that the rates of these transitions are strongly influenced by the permeant ion, suggesting that ion permeation regulates the voltage dependence of these channels.

biophysics↗

bioRxiv2021

Discovery and characterization of Hv1-type proton channels in reef-building corals.

Voltage-dependent proton-permeable channels are membrane proteins mediating a number of important physiological functions. Here we report the presence of a gene encoding for Hv1 voltage-dependent, proton-permeable channels in two species of reef-building corals. We performed a characterization of their biophysical properties and found that these channels are fast-activating and modulated by the pH gradient in a distinct manner. The biophysical properties of these novel channels make them interesting model systems. We have also developed an allosteric gating model that provides mechanistic insight into the modulation of voltage-dependence by protons. This work also represents the first functional characterization of any ion channel in scleractinian corals. We discuss the implications of the presence of these channels in the membranes of coral cells in the calcification and pH regulation processes and possible consequences of ocean acidification related to the function of these channels.

biophysics↗

bioRxiv2019

KV1.2 channels inactivate through a mechanism similar to C-type inactivation

C-type inactivation has been described in multiple voltage-gated K+ channels and in great detail in the Drosophila Shaker channel. As channels have moved into the structural era, atomic details of this and other gating mechanisms have started to be better understood. To date, the only voltage-gated channels whose structure has been solved are KvAP (X-ray diffraction), the KV1.2- KV2.1 \"paddle\" chimera (X-ray diffraction), KV1.2 (Cryo-EM); and ether-a-go-go (Cryo-EM) (Wang and MacKinnon, 2017), however, the characteristics and mechanisms of slow inactivation in these channels are unknown or poorly characterized. Here we present a detailed study of slow inactivation in the rat KV1.2 and show that it has some properties consistent with the C-type inactivation described in Shaker. We also study the effects of some mutations that are known to modulate C-type inactivation in Shaker and show that qualitative and quantitative differences exist in their functional effects, possibly underscoring subtle but important structural differences between the C-inactivated states in Shaker and KV1.2.

biophysics↗

bioRxiv2019

The contribution of the ankyrin repeat domain of TRPV1 as a thermal module

The TRPV1 cation non-selective ion channel plays an essential role in thermosensation and perception of other noxious stimuli. TRPV1 can be activated by low pH, high temperature or naturally occurring pungent molecules such as allicin, capsaicin or resiniferatoxin. Its noxious thermal sensitivity makes it an important participant as a thermal sensor in mammals. However, details of the mechanism of channel activation by increases in temperature remain unclear. Here we used a combination of approaches to try to understand the role of the ankyrin repeat domain (ARD) in channel behavior. First, a computational modeling approach by coarse-grained molecular dynamics simulation of the whole TRPV1 embedded in a phosphatidylcholine (POPC) and phosphatidylethanolamine (POPE) membrane provides insight into the dynamics of this channel domain. Global analysis of the structural ensemble shows that the ankyrin repeat domain is a region that sustains high fluctuations during dynamics at different temperatures. We then performed biochemical and thermal stability studies of the purified ARD by means of circular dichroism and tryptophan fluorescence and demonstrate that this region undergoes structural changes at similar temperatures that lead to TRPV1 activation. Our data suggest that the ARD is a dynamic module and that it may participate in controlling the temperature sensitivity of TRPV1.\n\nStatement of SignificanceThis work demonstrates that the temperature-dependent dynamics of the ankyrin repeat domain (ARD) of TRPV1 channels, as probed by coarse-grained molecular dynamics, corresponds to the experimentally determined dynamics of an isolated ARD domain. These results show that this region of TRPV1 channels undergoes significant conformational change as a function of increased temperature and suggest that it participates in the temperature-dependent structural changes that lead to channel opening.

biophysics↗

bioRxiv2018

Irreversible temperature gating in trpv1 sheds light on channel activation

Temperature activated TRP channels or thermoTRPs are among the only proteins that can directly convert temperature changes into changes in channel open probability. In spite of a wealth of information, including several experimentally determined structural models of TRP channels, the mechanism of temperature activation remains unknown. We have carefully characterized the repeated activation of TRPV1 by thermal stimuli and discovered a previously unknown inactivation process, which is irreversible. This inactivation is associated with specific conformational changes in the membrane proximal domain. We propose that this form of gating in TRPV1 channels is a consequence of the heat absorption process that leads to channel opening.

biophysics↗