Characterization and modeling of Ca2+ oscillations in mouse primary mesothelial cells

Abstract

Brief changes in the cytosolic and intra-organellar Ca2+ concentration serve as specific signals for various physiological processes. In mesothelial cells lining the surface of internal organs and the walls of body cavities, a re-entry in the cell cycle (G0-G1 transition) evoked by serum re-administration induces long-lasting Ca2+ oscillations with a slowly decreasing frequency. Individual mesothelial cells show a wide range of different oscillatory patterns within a single, supposedly homogenous cell population. Changes in the cytoplasmic Ca2+ concentration (ccyt) show baseline oscillatory patterns i.e., discrete Ca2+ transients starting from a constant basal ccyt level. The ER Ca2+ concentration (cER) displays a sawtooth wave at a semi-depleted ER state; the minimum level is reached just briefly after the maximal value for ccyt. These oscillations depend on plasmalemmal Ca2+ influx and on the inositol trisphosphate concentration [InsP3]; the Ca2+ influx is a crucial determinant of the oscillation frequency. Partial blocking of SERCA pumps modifies the oscillation frequency in both directions, i.e. increasing it in some cells and lowering it in others. Current mathematical models for Ca2+ oscillations mostly fail to reproduce two experimentally observed phenomena: the broad range of interspike intervals and constant basal ccyt levels between two Ca2+ spikes. Here we developed a new model based on--and fitted to--Ca2+ recordings of ccyt and cER recorded in primary mouse mesothelial cells. The model allowed for explaining many features of experimentally observed Ca2+ oscillations. We consider this model to be suitable to simulate various types of InsP3 receptor-based baseline Ca2+ oscillations.

Endogenous TRPV1 stimulation leads to the activation of the inositol phospholipid pathway necessary for sustained Ca2+ oscillations

“…S4). Extracellular release of ATP had been found to play an important role in generation of inositol phospholipid pathway [27,32]. This procedure applied to Du 145 cells resulted in the generation of similar oscillations in c cyt (80-95% responding cells), as was observed after CAPS treatment (Fig.…”

“…5B, C, E and F), we can conclude that this process does not play a critical role in phospholipase C activation. However, the transport of Ca 2+ ions across the plasma membrane is important for the maintenance of Ca 2+ oscillations and also affecting the oscillation frequency [27,32]. Thus, the amount of Ca 2+ ions passing through TRPV1 channels sustains Ca 2+ oscillations and influences the oscillation frequency (Fig.…”

“…The lowest and highest values are presented from the results of three independent experiments. Computerized peak recognition for frequency was realized via the Microsoft Excel 2010 environment as described before [27]; normalized recordings from 20 oscillating cells were evaluated. The oscillation frequency was determined for time window 1-5 min after CAPS administration.…”

Routes of Ca2+ Shuttling during Ca2+ Oscillations

“…Cell activation in a wide range of cell types results in Ca 2+ oscillations and in transient waves of increased c cyt ( 3 – 6 ). These oscillations (or waves) are not restricted to c cyt , but also c nucl ( 7 ), c ER ( 8 ), and c mito show Ca 2+ oscillations ( 9 ). The spatial extent of the oscillatory Ca 2+ signal is also important.…”

“…In Swiss 3T3 cells, serum-induced Ca 2+ changes are essential but not sufficient to induce NF-κB activation and subsequent DNA synthesis ( 16 ). In some cell types, Ca 2+ oscillations even persist in the absence of Ca 2+ influx across the plasma membrane ( 3 , 4 ), whereas in others, Ca 2+ oscillations strictly depend on Ca 2+ influx ( 5 , 8 ). Mitochondria influence cytosolic Ca 2+ oscillations in at least two ways.…”