No abstract

Two types of calcium (Ca2+) signaling-propagating intercellular Ca2+ waves of increasing intracellular Ca2+ concentration ([Ca2+]i) and nonpropagating oscillations in [Ca2+]i-co-exist in a variety of cell types. To investigate this difference in Ca2+ signaling, airway epithelial cells were loaded with heparin, an inositol 1,4,5-triphosphate (IP3) receptor antagonist, by pulsed, high-frequency electroporation. Heparin inhibited propagation of intercellular Ca2+ waves but not oscillations of [Ca2+]i. In heparin-free cells, Ca2+ waves propagated through cells displaying [Ca2+]i oscillations. Depletion of intracellular Ca2+ pools with the Ca2+-pump inhibitor thapsigargin also inhibited the propagation of Ca2+ waves. These studies demonstrate that the release of Ca2+ by IP3 is necessary for the propagation of intercellular Ca2+ waves and suggest that IP3 moves through gap junctions to communicate intercellular Ca2+ waves.

Intercellular communication of epithelial cells was examined by measuring changes in intracellular calcium concentration ([Ca2+]i). Mechanical stimulation of respiratory tract ciliated cells in culture induced a wave of increasing Ca2+ that spread, cell by cell, from the stimulated cell to neighboring cells. The communication of these Ca2+ waves between cells was restricted or blocked by halothane, an anesthetic known to uncouple cells. In the absence of extracellular Ca2+, the mechanically stimulated cell showed no change or a decrease in [Ca2+]i, whereas [Ca2+]i increased in neighboring cells. Iontophoretic injection of inositol 1,4,5-trisphosphate (IP3) evoked a communicated Ca2+ response that was similar to that produced by mechanical stimulation. These results support the hypothesis that IP3 acts as a cellular messenger that mediates communication through gap junctions between ciliated epithelial cells.

Abstract. Calcium signaling in C6 glioma cells in culture was examined with digital fluorescence video microscopy. C6 cells express low levels of the gap junction protein connexin43 and have correspondingly weak gap junctional communication as evidenced by dye coupling (Naus, C. C. G., J. E Bechberger, S. Caveney, and J. X. Wilson. 1991. Neurosci. Lett. 126:33-36

No abstract

The differentiating mouse oviduct has been used for the study of centriole morphogenesis because its epithelium is extensively ciliated and centriole formation occurs in a brief period after birth . Proliferative elements, consisting of an extensive fibrillar meshwork encrusted with 75 mµ granules, were encountered at all ages, but were the only centriole precursors present in younger animals (2-3 days) . These large aggregates were found either physically associated with a mature centriole or alone, but never associated with procentrioles . It is likely, therefore, that although proliferative elements may be derived from preexisting centrioles, they do not directly produce new centrioles . An intermediate structure, the condensation form, found primarily in older animals (4-6 days), and produced by the packing of the proliferative element material, gives rise to daughter procentrioles . This association of procentriole and condensation form has been called a generative complex . Condensation forms undergo various stages of depletion, producing hollow spheres with thin walls or small osmiophilic aggregates as procentrioles grow in length and assemble their microtubules . From these observations it is concluded that synthesis of microtubular precursor protein is mediated by the mature centriole and that this protein is packaged into many condensation forms in order to allow the rapid assembly of a large number of centrioles in a brief period of time .

Mechanical stimulation of a single cell in a primary mixed glial cell culture induced a wave of increased intracellular calcium concentration ([Ca2+]i) that was communicated to surrounding cells. Following propagation of the Ca2+ wave, many cells showed asynchronous oscillations in [Ca2+]i. Dantrolene sodium (10 microM) inhibited the increase in [Ca2+]i associated with this Ca2+ wave by 60-80%, and prevented subsequent Ca2+ oscillations. Despite the markedly decreased magnitude of the increase in [Ca2+]i, the rate of propagation and the extent of communication of the Ca2+ wave were similar to those prior to the addition of dantrolene. Thapsigargin (10 nM to 1 microM) induced an initial increase in [Ca2+]i ranging from 100 nM to 500 nM in all cells that was followed by a recovery of [Ca2+]i to near resting levels in most cells. Transient exposure to thapsigargin for 2 min irreversibly blocked communication of Ca2+ wave from the stimulated cell to adjacent cells. Glutamate (50 microM) induced an initial increase in [Ca2+]i in most cells that was followed by sustained oscillations in [Ca2+]i in some cells. Dantrolene (10 microM) inhibited this initial [Ca2+]i increase caused by glutamate by 65-90% and abolished subsequent oscillations. Thapsigargin (10 nM to 1 micron) abolished the response to glutamate in over 99% of cells. These results suggest that while both dantrolene and thapsigargin inhibit intracellular Ca2+ release, only thapsigargin affects the mechanism that mediates intercellular communication of Ca2+ waves. These findings are consistent with the hypothesis that inositol trisphosphate (IP3) mediates the propagation of Ca2+ waves whereas Ca(2+)-induced Ca2+ release amplifies Ca2+ waves and generates subsequent Ca2+ oscillations.

Respiratory tract ciliated cells, obtained from the rabbit trachea and maintained in culture, were sensitive to mechanical stimulation. The mechanical deformation of the cell surface induced a rapid, but transient, increase in ciliary beat frequency. In addition, the beat frequency of these ciliated cells was also increased in a dose-dependent manner by the beta-adrenergic drug isoproterenol (10(-7) to 10(-4) M) and by the calcium ionophore A23187 (10(-6) and 10(-5) M). To determine if drug and mechanosensitive activation of ciliary beat frequency arise from a common or different cellular mechanism, we investigated the effect of mechanical stimulation on beat frequency in the presence of isoproterenol or A23187. In isoproterenol (10(-8) to 10(-4) M), none of the parameters used to describe the ciliary beat frequency response to mechanical stimulation was altered. In A23187 (10(-6) M or above), the magnitude of the beat frequency response was significantly reduced or almost abolished, suggesting that mechanical stimulation acts, like A23187, to increase ciliary beat frequency by increasing intracellular calcium. Lower concentrations of A23187 had no effect. These results suggest that respiratory tract ciliated cells have at least two independent mechanisms for the control of ciliary beat frequency: one probably utilizing calcium, the other probably cAMP.