Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

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The Mechanosensitive BKα/β1 Channel Localizes to Cilia of Principal Cells in Rabbit Cortical Collecting Duct (CCD)

Within the CCD of the distal nephron of the rabbit, the BK (maxi K) channel mediates Ca2+.- and/or stretch-dependent flow-induced K+. secretion (FIKS) and contributes to K+. adaptation in response to dietary K+. loading. An unresolved question is whether BK channels in intercalated cells (ICs) and/or principal cells (PCs) in the CCD mediate these K+. secretory processes. In support of a role for ICs in FIKS is the higher density of immunoreactive apical BKalpha (pore-forming subunit) and functional BK channel activity than detected in PCs, and an increase in IC BKalpha expression in response to a high-K+. diet. PCs possess a single apical cilium which has been proposed to serve as a mechanosensor; direct manipulation of cilia leads to increases in cell Ca2+. concentration, albeit of nonciliary origin. Immunoperfusion of isolated and fixed CCDs isolated from control K+.-fed rabbits with channel subunit-specific antibodies revealed colocalization of immunodetectable BKalpha- and beta1-subunits in cilia as well as on the apical membrane of cilia-expressing PCs. Ciliary BK channels were more easily detected in rabbits fed a low-K+. vs. high-K+. diet. Single-channel recordings of cilia revealed K+. channels with conductance and kinetics typical of the BK channel. The observations that 1) FIKS was preserved but 2) the high-amplitude Ca2+. peak elicited by flow was reduced in microperfused CCDs subject to pharmacological deciliation suggest that cilia BK channels do not contribute to K+. secretion in this segment, but that cilia serve as modulators of cell signaling

Distinct epitopes on amiloride

Most Na(+)-selective transport proteins are inhibited by the drug amiloride. Studies using amiloride analogues suggest that specific regions of amiloride might participate in binding to receptors on these transport proteins. To determine whether certain domains of this drug are recognized as distinct epitopes, amiloride was coupled to albumin through either its C-5 NH2-group on the pyrazine ring or through a terminal NH2-group of the guanidino moiety, and antibodies were raised against these amiloride-albumin conjugates. Studies of antibody binding to amiloride analogues identified the 3,5-diaminopyrazinyl, the guanidinocarbonyl, and the C-6 halo moieties as distinct epitopes, although the antibodies required the presence of both the 3,5-diaminopyrazinyl as well as the guanidinocarbonyl moiety for binding

Activation of the Caenorhabditis elegans degenerin channel by shear stress requires the MEC-10 subunit

Mechanotransduction in Caenorhabditis elegans touch receptor neurons is mediated by an ion channel formed by MEC-4, MEC-10, and accessory proteins. To define the role of these subunits in the channel's response to mechanical force, we expressed degenerin channels comprising MEC-4 and MEC-10 in Xenopus oocytes and examined their response to laminar shear stress (LSS). Shear stress evoked a rapid increase in whole cell currents in oocytes expressing degenerin channels as well as channels with a MEC-4 degenerin mutation (MEC-4d), suggesting that C. elegans degenerin channels are sensitive to LSS. MEC-10 is required for a robust LSS response as the response was largely blunted in oocytes expressing homomeric MEC-4 or MEC-4d channels. We examined a series of MEC-10/MEC-4 chimeras to identify specific domains (amino terminus, first transmembrane domain, and extracellular domain) and sites (residues 130–132 and 134–137) within MEC-10 that are required for a robust response to shear stress. In addition, the LSS response was largely abolished by MEC-10 mutations encoded by a touch-insensitive mec-10 allele, providing a correlation between the channel's responses to two different mechanical forces. Our findings suggest that MEC-10 has an important role in the channel's response to mechanical forces