Local Ca2+ Entry Via Orai1 Regulates Plasma Membrane Recruitment of TRPC1 and Controls Cytosolic Ca2+ Signals Required for Specific Cell Functions

Store-operated Ca2+ entry (SOCE) has been associated with two types of channels: CRAC channels that require Orai1 and STIM1 and SOC channels that involve TRPC1, Orai1, and STIM1. While TRPC1 significantly contributes to SOCE and SOC channel activity, abrogation of Orai1 function eliminates SOCE and activation of TRPC1. The critical role of Orai1 in activation of TRPC1-SOC channels following Ca2+ store depletion has not yet been established. Herein we report that TRPC1 and Orai1 are components of distinct channels. We show that TRPC1/Orai1/STIM1-dependent ISOC, activated in response to Ca2+ store depletion, is composed of TRPC1/STIM1-mediated non-selective cation current and Orai1/STIM1-mediated ICRAC; the latter is detected when TRPC1 function is suppressed by expression of shTRPC1 or a STIM1 mutant that lacks TRPC1 gating, STIM1(684EE685). In addition to gating TRPC1 and Orai1, STIM1 mediates the recruitment and association of the channels within ER/PM junctional domains, a critical step in TRPC1 activation. Importantly, we show that Ca2+ entry via Orai1 triggers plasma membrane insertion of TRPC1, which is prevented by blocking SOCE with 1 µM Gd3+, removal of extracellular Ca2+, knockdown of Orai1, or expression of dominant negative mutant Orai1 lacking a functional pore, Orai1-E106Q. In cells expressing another pore mutant of Orai1, Orai1-E106D, TRPC1 trafficking is supported in Ca2+-containing, but not Ca2+-free, medium. Consistent with this, ICRAC is activated in cells pretreated with thapsigargin in Ca2+-free medium while ISOC is activated in cells pretreated in Ca2+-containing medium. Significantly, TRPC1 function is required for sustained KCa activity and contributes to NFκB activation while Orai1 is sufficient for NFAT activation. Together, these findings reveal an as-yet unidentified function for Orai1 that explains the critical requirement of the channel in the activation of TRPC1 following Ca2+ store depletion. We suggest that coordinated regulation of the surface expression of TRPC1 by Orai1 and gating by STIM1 provides a mechanism for rapidly modulating and maintaining SOCE-generated Ca2+ signals. By recruiting ion channels and other signaling pathways, Orai1 and STIM1 concertedly impact a variety of critical cell functions that are initiated by SOCE

The importance of determining the functional renal reserve in nephrological practice

Over the past decades, there has been an increase in the number of diseases of the urinary system in the world. Kidney diseases often acquire a long, progressive course with an outcome in chronic renal failure (CRF). An important feature of nephrological diseases is their propensity for progressive development. According to the latest data on the patterns of chronicity of kidney damage, the end result of a number of renal and non-renal diseases is the development of chronic kidney disease (CKD). The term "CKD" is known to have been coined by the American Association of Nephrologists in 2002. The criteria for determining CKD are: kidney damage lasting more than 3 months, which manifests itself in the form of structural or functional disorders of the organ's activity, with or without a decrease in the glomerular filtration rate (GFR) less than 60 ml per minute per 1.73 m2 in the presence or absence of other signs damage. Given the complex mechanism of GFR changes under physiological conditions, especially in pathology, it becomes necessary to measure filtration in active nephrons, as well as the total number of functioning nephrons. The only way to solve such problems today is to determine the functional renal reserve (FRR). It is important to note that the determination of GFR under conditions of relative functional rest is not sufficient in diagnosis, indicating only its overall value at the time of the study that is, about basal GFR, and does not always make it possible to correlate this indicator with the total number (mass) of nephrons which is especially important

20-Hydroxyeicosatetraenoic Acid (20-HETE) Is a Novel Activator of Transient Receptor Potential Vanilloid 1 (TRPV1) Channel*

Background: The P450 arachidonic acid metabolite, 20-HETE, is potently vasoactive and structurally related to known TRPV1 agonists

Characterization of TRPC channels in a heterologous system using calcium imaging and the patch-clamp technique

The family of transient receptor potential (TRPs) channels contains 28 mammalian members, each a unique cellular sensor that responds to a wide variety of external and internal signals. TRP channels are expressed by most mammalian cells, where they are involved in many different physiological functions. Canonical TRP channels (TRPCs) form a family of nonselective cationic channels, although with greater selectivity for Ca2+. This family is made up of seven members (TRPC1-7), all of which contain a TRP box in the carboxyl terminal and 3-4 ankyrin repeats in the amino terminal. While these channels share some similar properties, they display diverse gating mechanisms and are involved in different signaling pathways (Gees M et al., Compr Physiol, 2012). The activation or inhibition of these channels has been studied using different approaches and techniques. Here, we characterize the activation of the TRPC5 channel expressed in a heterologous system, using calcium imaging and the patch-clamp technique in whole-cell configuration.This work was supported by funds from the Spanish MINECO, SAF2016-77233-R cofinanced by the European Regional Development Fund (ERDF), and the “Severo Ochoa” Program for Centers of Excellence in R&D SEV-2013-0317.Peer reviewe