The visual systems of insects are exquisitely sensitive to motion. Over the past 40 years or so, motion processing in insects has been studied and characterised primarily through the optomotor response. This response, which is a turning response evoked by the apparent movement of the visual environment, serves to stabilise the insect's orientation with respect to the environment. Research over the past decade, however, is beginning to reveal the existence of a variety of other behavioural responses in insects, that use motion information in different ways. Here we review some of the recently characterised behaviours, describe the inferred properties of the underlying movement-detecting processes, and propose modified or new models to account for them.

We have investigated the functional consequences of three P/Q-type Ca 2؉ channel ␣1A (Ca v 2.1␣ 1 ) subunit mutations associated with different forms of ataxia (episodic ataxia type 2 (EA-2), R1279Stop, AY1593/1594D; progressive ataxia (PA), G293R). Mutations were introduced into human ␣1A cDNA and heterologously expressed in Xenopus oocytes or tsA-201 cells (with ␣ 2 ␦ and ␤1a) for electrophysiological and biochemical analysis. G293R reduced current density in both expression systems without changing single channel conductance. R1279Stop and AY1593/1594D protein were expressed in tsA-201 cells but failed to yield inward barium currents (I Ba ). However, AY1593/1594D mediated I Ba when expressed in oocytes. G293R and AY1593/1594D shifted the current-voltage relationship to more positive potentials and enhanced inactivation during depolarizing pulses (3 s) and pulse trains (100 ms, 1 Hz). Mutation AY1593/ 1594D also slowed recovery from inactivation. Single channel recordings revealed a change in fast channel gating for G293R evident as a decrease in the mean open time. Our data support the hypothesis that a pronounced loss of P/Q-type Ca 2؉ channel function underlies the pathophysiology of EA-2 and PA. In contrast to other EA-2 mutations, AY1593/1594D and G293R form at least partially functional channels.Genetic defects within the pore-forming Ca v 2.1␣ 1 (␣1A) subunit of neuronal voltage-gated P/Q-type Ca 2ϩ channels are associated with inherited human neurological diseases, such as Familial Hemiplegic Migraine (FHM), 1 Episodic Ataxia Type 2 (EA-2), progressive cerebellar ataxia, and epilepsy (1-6). Therefore, neuronal Ca 2ϩ channel dysfunction represents an important pathophysiological mechanism that may also underlie more common forms of migraine, epilepsy, and neurodegenerative processes.By mediating depolarization-induced Ca 2ϩ influx into dendrites, cell bodies, and nerve terminals, neuronal voltage-gated Ca 2ϩ channels control important neuronal processes. This includes fast neurotransmitter release, gene expression, neuronal plasticity, migration, and differentiation (7). P/Q-type Ca 2ϩ channels are very tightly coupled to neurotransmitter release in many neurons (see e.g. Refs. 8 and 9) and mediate most of the depolarization-induced Ca 2ϩ current in cerebellar Purkinje cells (10). They exist as hetero-oligomeric complexes of ␣1A subunits together with accessory subunits (especially ␣2␦ and ␤ (11)). ␣1A subunit-mediated neurotransmitter release is tightly controlled by other neurotransmitters (e.g. via protein kinase C phosphorylation and G-protein ␤␥ subunits (12-14)) and by their direct association with synaptic vesicles through soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins (15). Hence, these channels are ideally suited to fine-tune synaptic strength. This also explains why genetic defects, despite causing only minor changes in channel gating or expression, can lead to the above-mentioned clinical symptoms in humans and to the severe neurological abnormalities ...

STIM1 (stromal interaction molecule 1) and Orai proteins are the essential components of Ca(2+) release-activated Ca(2+) (CRAC) channels. We focused on the role of cholesterol in the regulation of STIM1-mediated Orai1 currents. Chemically induced cholesterol depletion enhanced store-operated Ca(2+) entry (SOCE) and Orai1 currents. Furthermore, cholesterol depletion in mucosal-type mast cells augmented endogenous CRAC currents, which were associated with increased degranulation, a process that requires calcium influx. Single point mutations in the Orai1 amino terminus that would be expected to abolish cholesterol binding enhanced SOCE to a similar extent as did cholesterol depletion. The increase in Orai1 activity in cells expressing these cholesterol-binding-deficient mutants occurred without affecting the amount in the plasma membrane or the coupling of STIM1 to Orai1. We detected cholesterol binding to an Orai1 amino-terminal fragment in vitro and to full-length Orai1 in cells. Thus, our data showed that Orai1 senses the amount of cholesterol in the plasma membrane and that the interaction of Orai1 with cholesterol inhibits its activity, thereby limiting SOCE.

Background and purposeThe glycerol-based lysophospholipid lysophosphatidylinositol (LPI) is an endogenous agonist of the G-protein-coupled receptor 55 (GPR55) exhibiting cannabinoid receptor-like properties in endothelial cells. To estimate the contribution of GPR55 to the physiological effects of LPI, the GPR55-dependent and -independent electrical responses in this cell type were investigated.Experimental approachApplying small interference RNA-mediated knock-down and transient overexpression, GPR55-dependent and -independent effects of LPI on cytosolic free Ca2+ concentration, membrane potential and transmembrane ion currents were studied in EA.hy296 cells.Key resultsIn a GPR55-dependent, GDPβS and U73122-sensitive manner, LPI induced rapid and transient intracellular Ca2+ release that was associated with activation of charybdotoxin–sensitive, large conductance, Ca2+-activated, K+ channels (BKCa) and temporary membrane hyperpolarization. Following these initial electrical reactions, LPI elicited GPR55-independent long-lasting Na+ loading and a non-selective inward current causing sustained membrane depolarization that depended on extracellular Ca2+ and Na+ and was partially inhibited by Ni2+ and La3+. This inward current was due to the activation of a voltage-independent non-selective cation current. The Ni2+ and La3+-insensitive depolarization with LPI was prevented by inhibition of the Na/K-ATPase by ouabain.Conclusions and implicationsLPI elicited a biphasic response in endothelial cells of which the immediate Ca2+ signalling depends on GPR55 while the subsequent depolarization is due to Na+ loading via non-selective cation channels and an inhibition of the Na/K-ATPase. Thus, LPI is a potent signalling molecule that affects endothelial functions by modulating several cellular electrical responses that are only partially linked to GPR55.

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