Capacitative calcium entry: sensing the calcium stores

A long-standing mystery in the cell biology of calcium channel regulation is the nature of the signal linking intracellular calcium stores to plasma membrane capacitative calcium entry channels. An RNAi-based screen of selected Drosophila genes has revealed that a calcium-binding protein, stromal interaction molecule (STIM), plays an essential role in the activation of these channels and may be the long sought sensor of calcium store content

MECHANISMS OF DRUG DISTRIBUTION IN RAT SUBMAXILLARY GLAND IN VITRO

The access of drugs to variofis sites of action in the body is impeded by a succession of membranes. Likewise, the removal of a drug or foreign substance from the body is similarly dependent on the ability of the substance under consideration to permeate biological barriers. A con-committant problem generally arises concerning the overall time course of drug action: that of drug storage through binding or similar processes. Schanker (196h) however, has stated that Although the mechanisms of localization and those of membrane transfer are in many respects different problems, there are some instances in which they are inseparable parts of the same problem. Examples include phenomena whereby the binding of a substance to the cell membrane is required for transport (Rosenberg and Wilbrandt, 1955; Peters; 1960; Lacko and Burger, 1961; Schwartz and Matsui, 1967; Stein, 1967). From a functional standpoint, body membranes may be classified in three major categories (Schanker, 1962b); membranes several cell layers thick such as skin, those one cell layer thick such as the brush border epithelium of the intestine, and membranes less than one cell in thickness such as the cell membrane itself or the membranes of organelles (e.g. mitochondria). Thus, except for the barriers associated with subcellular structures, the cell membrane 6 (or plasma membrane as it is often called) may be considered the fundamental unit of body membranes in general

ATP-induced calcium mobilization and inositol 1,4,5-trisphosphate formation in H-35 hepatoma cells

AbstractAddition of ATP (but not epinephrine, angiotensin II, vasopressin, or platelet-activating factor) to H-35 hepatoma cells whose cellular lipids have been pre-labelled with [3H]inositol, causes a rapid increase in [3H]inositol trisphosphate. In H-35 cells pre-incubated in the presence of 45Ca2+, ATP causes a similarly rapid release of 45Ca2+. The concentration-effect relationships for inositol trisphosphate formation and Ca2+ efflux are similar to those reported previously for differentiated hepatocytes. These results demonstrate that at least one of the Ca2+-mobilizing receptors normally found on hepatocytes is functionally retained in the H-35 hepatoma cell line and thus could provide a useful model for the study of these receptor mechanisms in liver

Multiscale imaging of basal cell dynamics in the functionally mature mammary gland

The mammary epithelium is indispensable for the continued survival of more than 5,000 mammalian species. For some, the volume of milk ejected in a single day exceeds their entire blood volume. Here, we unveil the spatiotemporal properties of physiological signals that orchestrate the ejection of milk from alveolar units and its passage along the mammary ductal network. Using quantitative, multidimensional imaging of mammary cell ensembles from GCaMP6 transgenic mice, we reveal how stimulus evoked Ca oscillations couple to contractions in basal epithelial cells. Moreover, we show that Ca-dependent contractions generate the requisite force to physically deform the innermost layer of luminal cells, compelling them to discharge the fluid that they produced and housed. Through the collective action of thousands of these biological positive-displacement pumps, each linked to a contractile ductal network, milk begins its passage toward the dependent neonate, seconds after the command

Activation of store-operated calcium entry in airway smooth muscle cells: insight from a mathematical model

Intracellular dynamics of airway smooth muscle cells (ASMC) mediate ASMC contraction and proliferation, and thus play a key role in airway hyper-responsiveness (AHR) and remodelling in asthma. We evaluate the importance of store-operated entry (SOCE) in these dynamics by constructing a mathematical model of ASMC signaling based on experimental data from lung slices. The model confirms that SOCE is elicited upon sufficient depletion of the sarcoplasmic reticulum (SR), while receptor-operated entry (ROCE) is inhibited in such conditions. It also shows that SOCE can sustain agonist-induced oscillations in the absence of other influx. SOCE up-regulation may thus contribute to AHR by increasing the oscillation frequency that in turn regulates ASMC contraction. The model also provides an explanation for the failure of the SERCA pump blocker CPA to clamp the cytosolic of ASMC in lung slices, by showing that CPA is unable to maintain the SR empty of . This prediction is confirmed by experimental data from mouse lung slices, and strongly suggests that CPA only partially inhibits SERCA in ASMC

STIM2 regulates PKA-dependent phosphorylation and trafficking of AMPARs

STIMs (STIM1 and STIM2 in mammals) are transmembrane proteins that reside in the endoplasmic reticulum (ER) and regulate store-operated Ca2+ entry (SOCE). The function of STIMs in the brain is only beginning to be explored, and the relevance of SOCE in nerve cells is being debated. Here we identify STIM2 as a central organizer of excitatory synapses. STIM2, but not its paralogue STIM1, influences the formation of dendritic spines and shapes basal synaptic transmission in excitatory neurons. We further demonstrate that STIM2 is essential for cAMP/PKA-dependent phosphorylation of the AMPA receptor (AMPAR) subunit GluA1. cAMP triggers rapid migration of STIM2 to ER–plasma membrane (PM) contact sites, enhances recruitment of GluA1 to these ER-PM junctions, and promotes localization of STIM2 in dendritic spines. Both biochemical and imaging data suggest that STIM2 regulates GluA1 phosphorylation by coupling PKA to the AMPAR in a SOCE-independent manner. Consistent with a central role of STIM2 in regulating AMPAR phosphorylation, STIM2 promotes cAMP-dependent surface delivery of GluA1 through combined effects on exocytosis and endocytosis. Collectively our results point to a unique mechanism of synaptic plasticity driven by dynamic assembly of a STIM2 signaling complex at ER-PM contact sites