The role of circadian rhythm and environmental factors in the regulation of sea urchin spawning.

Simultaneous video recording of the sea urchin spawning behavior and recording of environmental factors enabled us to found synergism of the effects of circadian rhythm and phytoplankton on the spawning activity of the sea urchin Strongylocentrotus intermedius (Agassiz, 1864).

[Lipid composition of mechanosensitive cell cilia and mechanoreceptor organ of bivalve molluscs]. / Osobennosti lipidnykh sostavov resnichek mekhanochuvstvitel'nykh kletok i mekhanoretseptornogo organa dvustvorchatykh molliuskov.

The lipid composition of the mechanoreceptive organ of two marine molluscs in comparison with other molluscan tissues and of isolated cilia of sense organ hair cells in comparison with the gill cilia has been studied. It was shown that the lipid composition of the mechanoreceptive organ differs in a number of features from that of other organs and that the ratios of individual phospholipid classes vary in cilia and intact organs. Ciliary aminophospholipids make up to approximately 89%, whereas choline-containing phospholipids--only 6-8% of the total phospholipid pool. No qualitative phospholipid differences between sense cell cilia and gill cilia were found. However, hair cell cilia contain less phosphatidylethanolamine and choline phospholipids, but more phosphatidylserine and phosphatidylinositol. This suggests that the observed peculiarities of hair cell cilia may play a role in the maintenance of the proper arrangement of hair bundles and the distance between the cilium and stereovilli and/or in the regulation of Ca2(+)-dependent processes.

[Role of calcium ions in the generation of abdominal sense organ response in the scallop]. / Rol'ionov kal'tsiia v generatsii otveta abdominal'nogo sensornogo organa molliuska grebeshka.

The effect of a Ca2+-free solution, Cd2+ ions and theophylline on compound response recorded from the nerve which originates from the abdominal sensory organ of the scallop (Patinopecten yessoensis) was studied during mechanical stimulation of this organ. It was shown that the elimination of Ca2+ ions from the extracellular medium or addition of 10 mmol/l Cd2+ caused complete reversible block of the response. The addition of 5 mmol/l theophylline to the medium resulted in a significant increase in the amplitude of the response. These data show participation of Ca2+ ions in the process of the mechanical stimulus transformation into electrical signal as well as a possible regulation of this process by intracellular cAMP-dependent reactions.

[Functional features of the electroreceptors of several electric and non-electric fish]. / Funktsional'nye osobennosti élektroretseptorov nekotorykh élektricheskikh i neélektricheskikh ryb

The effect of the electric, magnetic, and mechanical stimulation of the electroreceptors was studied in marine skates (Trigon pastinaca, Raja clavata, and Torpedo marmorata) by recording single nerve fiber responses. The following two types of backbround dischanges were found with regular activity and bursting. In some fibres the bursts of impulses appeared simultaneously with respiration while in the others the activity was suppressed. The current threshold of the clear-cut responses were equal to 10- minus 9--10- minus 11 A/mm-2. The activity of the electroredeptors was modified by introducing a conductive or nonconductive object into the water. High sensistivity of the electroreceptors to weak magnetic field was shown. The biological role of the electroreceptors is discussed.

[The effect of sodium, potassium and calcium ions on the functional characteristics of catfish electroreceptors]. / Vliianie ionov natriia, kaliia i kal'tsiia na funktsional'nye kharakteristiki élektroretseptorov karlikovykh somikov

Afferent responses of single afferent fibre from small pit organs to various concentration of potassium, sodium and calcium ions were studied in the catfish (Ictalurus nebulosus). The receptors were stimulated with d. c. pulses. Calcium concentration between 0.4-5 mM/1 were practically ineffective. Calcium concentration from 5 to 100 7m/1 increased the threshold to electrical stimulation. 2mM/1 sodium and potassium solutions caused an increase in the threshold to the anodic stimuli and elimination of the responses to the cathodic ones. This effect disappeared after the addition of 0.4 mM/1 CaCl2 or application of long anodic stimuli of great intensity (10(-8)-10(-7) A/mm2). With an increase in potassium concentration to 10-20 mM/1 the threshold returned to the initial level. Potassium concentrations above 20 mM/1 increased the threshold to electrical stimuli. The effect of ions was compared with the action of electric current.

[Functional characteristics of electroreceptors (small pitted organs) of the dwarf catfish]. / Nekotorye funktsional;nye osobennosti élektroretseptorov (malykh iamchatykh organov) karlikovykh somikov

The response characteristics of the small pit organs in the catfish Ictalurus nebulosus to electrical stimuli of various polarities, intensities and durations were investigated using the recording of electrical activity from single nerve fibres of the lateral nerve. The fibres showed background activity either rhythmical (35-45 imp/s) or modulated by fish swimming movements. The current density thresholds were in a range of 10 minus 10 -10 minus 11 /mm-2. Electrical stimulation evoked a phasic-tonic response in the electroreceptor fibres. The latencies varied from 10 to 50 ms for on-responses and from 10 to 200 ms for off-responses. Certain units responded with excitation to strong cathodal stimulation, and with excitatory response to anodal stimulus of weak or moderate intensity. The properties of small pit organs and other electroreceptors are compared.