MHV-A59 Gene 1 Proteins are Associated with Two Distinct Membrane Populations

The leukocyte response integrin (LRI) is a phagocyte integrin which recognizes the basement membrane protein entactin and the synthetic peptide Lys-Gly-Ala-Gly-Asp-Val (KGAGDV). The function of LRI is intimately associated with that of a distinct membrane protein, integrin-associated protein (IAP), as antibodies which recognizes IAP can inhibit all known functions of LRI. When adherent to surface, the LRI ligands entactin and KGAGDV activate the respiratory burst in polymorphonuclear leukocytes (PMN) and monocytes, as do monoclonal antibodies (mAb) directed at either LRI or IAP. When added in solution, peptides and antibodies specific for LRI, and some, but not all, anti-IAP antibodies, can inhibit the respiratory burst activated by any of these surface-adherent ligands. Only monoclonal anti-IAP antibodies which can inhibit LRI function when added in solution are competent to activate the respiratory burst when adherent to a surface. KGAGDV peptide and anti-LRI added in solution can inhibit anti-IAP-stimulated respiratory burst. The LRI-IAP-initiated respiratory burst is independent of CD18, as judged by: (a) blockade of inhibition by anti-CD18 mAb with the protein kinase A inhibitor HA1004; (b) enhanced sensitivity of CD18-dependent respiratory burst compared with LRI/IAP-dependent respiratory burst to the tyrosine kinase inhibitors genestein and herbimicin; and (c) generation of a respiratory burst in response to KGAGDV, anti-LRI, and anti-IAP coated surfaces in PMN from a patient with LAD. Despite its apparent CD18 independence, LRI/IAP-initiated respiratory burst requires a solid phase ligand and is sensitive to cytochalasin B. These data suggest a model in which LRI and IAP act together as a single signal transduction unit to activate the phagocyte respiratory burst, in a manner that requires CD18-independent cell adhesion.

Download Full-text

ION-INDUCED ULTRASTRUCTURAL TRANSFORMATIONS IN ISOLATED MITOCHONDRIA

The Journal of Cell Biology ◽

10.1083/jcb.42.1.221 ◽

1969 ◽

Vol 42 (1) ◽

pp. 221-234 ◽

Cited By ~ 77

Author(s):

Charles R. Hackenbrock ◽

Arnold I. Caplan

Keyword(s):

Marked Decrease ◽

Active Form ◽

Liver Mitochondria ◽

Rat Liver Mitochondria ◽

Dense Matrix ◽

Low Levels ◽

Osmolar Concentration ◽

Oriented Membranes ◽

Ultrastructural Transformation ◽

Distinct Membrane

The energized uptake of low levels of Ca2+ in the presence and absence of phosphate by isolated rat liver mitochondria, and the perturbation effected by this activity on ultrastructural and metabolic parameters of mitochondria have been investigated. In the presence of phosphate, low levels of Ca2+ are taken up by mitochondria and result in various degrees of ultrastructural expansion of the inner mitochondrial compartment. This indicates that low levels of Ca2+ in the presence of phosphate, are accumulated in an osmotically active form into the water phase of the inner compartment. The first clearly observable quantitative increase in the volume of the inner compartment occurs after the accumulation of 100 nmoles Ca2+/mg protein. An accumulation of 150–200 nmoles Ca2+/mg protein, which is equivalent to the osmolar concentration of endogenous K+, is required to effect a doubling of the volume of the inner compartment. This degree of osmotic perturbation occurs as mitochondria transform from a condensed to an orthodox conformation. The osmotically induced orthodox conformation differs from the mechanochemically induced orthodox conformation previously described, in that its development is concomitant with a marked decrease in acceptor control and oxidative phosphorylation efficiency and it fails to transform to a condensed conformation in response to addition of ADP. In the absence of added phosphate, a maximum of 190 nmoles Ca2+/mg protein was found to be taken up by mitochondria (state 6). Ca2+ is apparently bound under state 6 conditions since the uptake does not effect an ultrastructural expansion of the inner compartment. Phosphate added after state 6 Ca2+ binding, however, results in an immediate ultrastructural expansion of the inner compartment. The addition of phosphate to mitochondria in the absence of exogenous Ca2- fails to effect an osmotic ultrastructural transformation. Under state 6 conditions, the binding of between 40 and 190 nmoles Ca2+/mg protein results in the formation of dense matrix inclusions which appear to be composed of tightly packed, concentrically oriented membranes. Under conditions in which the bound Ca2+ is subsequently released, there is a concomitant loss in the density of these matrix inclusions, leaving behind morphologically distinct membrane whorls in the mitochondrial matrix.

Download Full-text

Regulation of nephron water and electrolyte transport by adenylyl cyclases

AJP Renal Physiology ◽

10.1152/ajprenal.00656.2013 ◽

2014 ◽

Vol 306 (7) ◽

pp. F701-F709 ◽

Cited By ~ 13

Author(s):

Timo Rieg ◽

Donald E. Kohan

Keyword(s):

Hormonal Regulation ◽

Electrolyte Transport ◽

Adenylyl Cyclases ◽

Disease Pathogenesis ◽

Membrane Bound ◽

G Protein Coupled ◽

Camp Formation ◽

Distinct Membrane ◽

Genetically Modified Animals

Adenylyl cyclases (AC) catalyze formation of cAMP, a critical component of G protein-coupled receptor signaling. So far, nine distinct membrane-bound AC isoforms (AC1-9) and one soluble AC (sAC) have been identified and, except for AC8, all of them are expressed in the kidney. While the role of ACs in renal cAMP formation is well established, we are just beginning to understand the function of individual AC isoforms, particularly with regard to hormonal regulation of transporter and channel phosphorylation, membrane abundance, and trafficking. This review focuses on the role of different AC isoforms in regulating renal water and electrolyte transport in health as well as potential pathological implications of disordered AC isoform function. In particular, we focus on modulation of transporter and channel abundance, activity, and phosphorylation, with an emphasis on studies employing genetically modified animals. As will be described, it is now evident that specific AC isoforms can exert unique effects in the kidney that may have important implications in our understanding of normal physiology as well as disease pathogenesis.

Download Full-text

Calnexin revealed as an ether-a-go-go chaperone by getting mutant worms up and going

The Journal of General Physiology ◽

10.1085/jgp.201812068 ◽

2018 ◽

Vol 150 (8) ◽

pp. 1059-1061

Author(s):

Jonathan T. Pierce

Keyword(s):

Ion Channels ◽

Dynamic Control ◽

Cell Types ◽

K Channel ◽

Membrane Domains ◽

Excitable Cells ◽

Patch Clamp Recording ◽

Cell Excitability ◽

Distinct Membrane

The role of ion channels in cell excitability was first revealed in a series of voltage clamp experiments by Hodgkin and Huxley in the 1950s. However, it was not until the 1970s that patch-clamp recording ushered in a revolution that allowed physiologists to witness how ion channels flicker open and closed at angstrom scale and with microsecond resolution. The unexpectedly tight seal made by the patch pipette in the whole-cell configuration later allowed molecular biologists to suck up the insides of identified cells to unveil their unique molecular contents. By refining these techniques, researchers have scrutinized the surface and contents of excitable cells in detail over the past few decades. However, these powerful approaches do not discern which molecules are responsible for the dynamic control of the genesis, abundance, and subcellular localization of ion channels. In this dark territory, teams of unknown and poorly understood molecules guide specific ion channels through translation, folding, and modification, and then they shuttle them toward and away from distinct membrane domains via different subcellular routes. A central challenge in understanding these processes is the likelihood that these diverse regulatory molecules may be specific to ion channel subtypes, cell types, and circumstance. In work described in this issue, Bai et al. (2018. J. Gen. Physiol. https://doi.org/10.1085/jgp.201812025) begin to shed light on the biogenesis of UNC-103, a K+ channel found in Caenorhabditis elegans.

Download Full-text

Basal-lateral and intracellular membrane populations of rat exorbital lacrimal gland

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1983.245.1.g133 ◽

1983 ◽

Vol 245 (1) ◽

pp. G133-G142

Author(s):

A. K. Mircheff ◽

C. N. Conteas ◽

C. C. Lu ◽

N. A. Santiago ◽

G. M. Gray ◽

...

Keyword(s):

Atpase Activity ◽

Lacrimal Gland ◽

Membrane Vesicle ◽

Sedimentation Coefficient ◽

Plasma Membrane Vesicle ◽

Intracellular Membrane ◽

Lateral Membrane ◽

Specific Activities ◽

Analytical Fractionation ◽

Distinct Membrane

With the goal of isolating and identifying plasma membrane vesicle populations from epithelial cells of the rat exorbital lacrimal gland, we have designed an analytical fractionation of homogenates of the gland parenchyma. This fractionation utilizes separation procedures based on three independent physical properties of subcellular particles: sedimentation coefficient, density, and density after interaction of membrane cholesterol with digitonin. A commonly accepted marker for basal-lateral membranes, Na-K-ATPase, is associated with at least two physically distinct membrane populations. One population can be identified as basal-lateral membrane fragments on the basis of its fractional and specific contents of Na-K-ATPase; it accounts for 50% of the total Na-K-ATPase activity, enriched 29-fold with respect to the initial homogenate. With these values we calculate that the sample of basal membranes has been purified 60-fold with respect to the initial homogenate. The remaining Na-K-ATPase activity appears to be associated, at three- to fivefold lower specific activities, with intracellular membrane populations. We speculate that these populations have been derived from the Golgi complex.

Download Full-text