Gram-negative bacterial infections are accompanied by inflammation and somatic or visceral pain. These symptoms are generally attributed to sensitization of nociceptors by inflammatory mediators released by immune cells. Nociceptor sensitization during inflammation occurs through activation of the Toll-like receptor 4 (TLR4) signalling pathway by lipopolysaccharide (LPS), a toxic by-product of bacterial lysis. Here we show that LPS exerts fast, membrane delimited, excitatory actions via TRPA1, a transient receptor potential cation channel that is critical for transducing environmental irritant stimuli into nociceptor activity. Moreover, we find that pain and acute vascular reactions, including neurogenic inflammation (CGRP release) caused by LPS are primarily dependent on TRPA1 channel activation in nociceptive sensory neurons, and develop independently of TLR4 activation. The identification of TRPA1 as a molecular determinant of direct LPS effects on nociceptors offers new insights into the pathogenesis of pain and neurovascular responses during bacterial infections and opens novel avenues for their treatment.

Hypoxic inhibition of large-conductance Ca ²⁺ -dependent K ⁺ channels (maxiK) of rat carotid body type I cells is a well-established fact. However, the molecular mechanisms of such inhibition and the role of these channels in the process of hypoxic transduction remain unclear. We have examined the mechanisms of interaction of O ₂ with maxiK channels exploring the effect of hypoxia on maxiK currents recorded with the whole-cell and the inside-out configuration of the patch-clamp technique. Hypoxia inhibits channel activity both in whole-cell and in excised membrane patches. This effect is strongly voltage- and Ca ²⁺ -dependent, being maximal at low [Ca ²⁺ ] and low membrane potential. The analysis of single-channel kinetics reveals a gating scheme comprising three open and five closed states. Hypoxia inhibits channel activity increasing the time the channel spends in the longest closed states, an effect that could be explained by a decrease in the Ca ²⁺ sensitivity of those closed states. Reducing maxiK channels with dithiothreitol (DTT) increases channel open probability, whereas oxidizing the channels with 2,2′-dithiopyridine (DTDP) has the opposite effect. These results suggest that hypoxic inhibition is not related with a reduction of channel thiol groups. However, CO, a competitive inhibitor of O ₂ binding to hemoproteins, fully reverts hypoxic inhibition, both at the whole-cell and the single-channel level. We conclude that O ₂ interaction with maxiK channels does not require cytoplasmic mediators. Such interaction could be mediated by a membrane hemoprotein that, as an O ₂ sensor, would modulate channel activity.

Voltage-gated K⁺ (K_V) channels are protein complexes composed of ion-conducting integral membrane α subunits and cytoplasmic modulatory β subunits. The differential expression and association of α and β subunits seems to contribute significantly to the complexity and heterogeneity of K_V channels in excitable cells, and their functional expression in heterologous systems provides a tool to study their regulation at a molecular level. Here, we have studied the effects of Kvβ1.2 coexpression on the properties of Shaker and Kv4.2 K_V channel α subunits, which encode rapidly inactivating A-type K⁺ currents, in transfected HEK293 cells. We found that Kvβ1.2 functionally associates with these two α subunits, as well as with the endogenous K_V channels of HEK293 cells, to modulate different properties of the heteromultimers. Kvβ1.2 accelerates the rate of inactivation of the Shaker currents, as previously described, increases significantly the amplitude of the endogenous currents, and confers sensitivity to redox modulation and hypoxia to Kv4.2 channels. Upon association with Kvβ1.2, Kv4.2 can be modified by DTT (1,4 dithiothreitol) and DTDP (2,2′-dithiodipyridine), which also modulate the low pO₂ response of the Kv4.2+β channels. However, the physiological reducing agent GSH (reduced glutathione) did not mimic the effects of DTT. Finally, hypoxic inhibition of Kv4.2+β currents can be reverted by 70% in the presence of carbon monoxide and remains in cell-free patches, suggesting the presence of a hemoproteic O₂ sensor in HEK293 cells and a membrane-delimited mechanism at the origin of hypoxic responses. We conclude that β subunits can modulate different properties upon association with different K_V channel subfamilies; of potential relevance to understanding the molecular basis of low pO₂ sensitivity in native tissues is the here described acquisition of the ability of Kv4.2+β channels to respond to hypoxia.

Mutations in human LPIN2 produce a disease known as Majeed syndrome, the clinical manifestations of which are ameliorated by strategies that block IL-1β or its receptor. However the role of lipin-2 during IL-1β production remains elusive. We show here that lipin-2 controls excessive IL-1β formation in primary human and mouse macrophages by several mechanisms, including activation of the inflammasome NLRP3. Lipin-2 regulates MAPK activation, which mediates synthesis of pro–IL-1β during inflammasome priming. Lipin-2 also inhibits the activation and sensitization of the purinergic receptor P2X7 and K+ efflux, apoptosis-associated speck-like protein with a CARD domain oligomerization, and caspase-1 processing, key events during inflammasome activation. Reduced levels of lipin-2 in macrophages lead to a decrease in cellular cholesterol levels. In fact, restoration of cholesterol concentrations in cells lacking lipin-2 decreases ion currents through the P2X7 receptor, and downstream events that drive IL-1β production. Furthermore, lipin-2–deficient mice exhibit increased sensitivity to high lipopolysaccharide doses. Collectively, our results unveil lipin-2 as a critical player in the negative regulation of NLRP3 inflammasome.

Native cardiac and skeletal muscle Na channels are complexes of alpha and beta 1 subunits. While structural correlates for activation, inactivation, and permeation have been identified in the alpha subunit and the expression of alpha alone produces functional channels, beta 1-deficient rat skeletal muscle (mu 1) and brain Na channels expressed in Xenopus oocytes do not gate normally. In contrast, the requirement of a beta 1 subunit for normal function of Na channels cloned from rat heart or human heart (hH1) has been disputed. Coinjection of rat brain beta 1 subunit cRNA with hH1 (or mu 1) alpha subunit cRNA into oocytes increased peak Na currents recorded 2 d after injection by 240% (225%) without altering the voltage dependence of activation. In mu 1 channels, steady state inactivation was shifted to more negative potentials (by 6 mV, p < 0.01), but the shift of 2 mV was not significant for hH1 channels. Nevertheless, coexpression with beta 1 subunit speeded the decay of macroscopic current of both isoforms. Ensemble average hH1 currents from cell-attached patches revealed that coexpression of beta 1 increases the rate of inactivation (quantified by time to 75% decay of current; p < 0.01 at -30, -40, and -50 mV). Use-dependent decay of hH1 Na current during repeated pulsing to -20 mV (1 s, 0.5 Hz) after a long rest was reduced to 16 +/- 2% of the first pulse current in oocytes coexpressing alpha and beta 1 subunits compared to 35 +/- 8% use-dependent decay for oocytes expressing the alpha subunit alone. Recovery from inactivation of mu 1 and hH1 Na currents after 1-s pulses to -20 mV is multiexponential with three time constants; coexpression of beta 1 subunit decreased all three recovery time constants. We conclude that the beta 1 subunit importantly influences the function of Na channels produced by coexpression with either the hH1 or mu 1 alpha subunits.