Changes in gravity rapidly alter the magnitude and direction of a cellular calcium current

Abstract

In single-celled spores of the fern Ceratopteris richardii, gravity directs polarity of development and induces a directional, trans-cellular calcium (Ca(2+)) current. To clarify how gravity polarizes this electrophysiological process, we measured the kinetics of the cellular response to changes in the gravity vector, which we initially estimated using the self-referencing calcium microsensor. In order to generate more precise and detailed data, we developed a silicon microfabricated sensor array which facilitated a lab-on-a-chip approach to simultaneously measure calcium currents from multiple cells in real time. These experiments revealed that the direction of the gravity-dependent polar calcium current is reversed in less than 25 s when the cells are inverted, and that changes in the magnitude of the calcium current parallel rapidly changing g-forces during parabolic flight on the NASA C-9 aircraft. The data also revealed a hysteresis in the response of cells in the transition from 2g to micro-g in comparison to cells in the micro-g to 2-g transition, a result consistent with a role for mechanosensitive ion channels in the gravity response. The calcium current is suppressed by either nifedipine (calcium-channel blocker) or eosin yellow (plasma membrane calcium pump inhibitor). Nifedipine disrupts gravity-directed cell polarity, but not spore germination. These results indicate that gravity perception in single plant cells may be mediated by mechanosensitive calcium channels, an idea consistent with some previously proposed models of plant gravity perception.

Possible Role of Non-Muscle Alpha-Actinins in Muscle Cell Mechanosensitivity

“…In particular, extracellular matrix and membrane proteins, components of ion channels, cytoskeletal compounds and intracellular structures may serve as mechanosensors [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43]. But almost all possible mechanisms of primary mechanotransduction depend on the condition of the submembranous cortical cytoskeleton, the structural integrity of which determines the mechanical properties of the certain type of cell and is reflected in the cell stiffness.…”

Molecular mechanisms of gravity perception and signal transduction in plants

“…In unicellular spores of the ceratodon Ceratopteris richardii, a transcellular calcium flux from the extracellular medium to the lower side of cells and from the upper side to the extracellular medium was detected by calcium-sensitive electrodes. This flux changes its orientation during 25 s of gravistimulation (Salmi et al 2011). In cells of stem endodermis of the creeping Chrysanthemum morifolium, calcium deposition in cytoplasm was shown to be increased after 5 min of gravistimulation.…”

“…Exogenous calcium application enhances root and hypocotyl gravity responses, while inhibitors of mechanosensitive ion channels, calcium channels, and Ca 2+ -ATPases interfere with gravitropism (Bushart et al 2013(Bushart et al , 2014Perera et al 2006;Salmi et al 2011;Urbina et al 2006;Zhang et al 2011a). Specific inhibitors were also used to demonstrate that gravity induces stretch-activated channels to release ATP along the lower side of the spore cell.…”

Mathematical Modeling in Cell Biomechanics: Myofibrils Contractile Activity

“…Cell membrane mechanical stretching, for example, using patch-clump technology change mechanosensitive ion channels cation-transport activity as a result of conformation changes in either lipid bilayer [11] [12] or the very channel gate domain [13]. Plant cell reorientation in a gravity field results in calcium flow change within 25 seconds, arguing of calcium channels to be mechanosensitive [14]. External mechanic tension leads to calcium leakages from broken bone matrix [15].…”