Diatom assemblages in superficial sediments from the Gulf of Riga,eastern Baltic Sea

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.The results seem to imply that the number of taxa and the abundance of the frustules are affected by runoff from rivers and the degree of eutrophication in different parts of the Gulf. Areas with high eutrophication, e.g. the river estuaries, have diatom assemblages of varying composition, while in areas with moderate eutrophication the composition is almost constant and the influx of freshwater diatoms and littoral periphyton small. The high abundance and low diversity of brackish-marine and brackish, planktonic diatoms seem to be a result of an influx of nutrients and pollutants in the water and bottom sediments. The sea ice diatoms occurring in the Baltic waters and also in the Gulf of Riga tend to be resistant to eutrophication or are even favoured by it.     

Anisotropy of stationary rates and delays in extrasystolic waves in the dog heart]

Excitation propagation in the ventricle and auricle bands of the dog's myocardium has been studied. The anisotropy of stationary valocities and delays of the initiation of extrasistole exciation has been shown: along the fibres the velocity is higher and the delay smaller than across the fibres. The levels of anisotropy of velocities and delays are almost equal in each structure. The strongest anisotropy of delays and velocities (-4,5) is observed in the ventricle muscle layer; the weakest (1,7)-in a specialized layer. The anisotropy of velocities and delays is the greater, the greater is the electrotone anisotropy. A new mechanism of extrasistole initiation (reentry) in the system homogenous by the membrane properties, but with anisotropy of intercellular bonds is considered.     

Potential- and stimulus-dependence of the effect of dihydropyridine Ca-agonists on calcium channels in heart fibers

It has been shown on the frog auricle fibres by the method of double sucrose bridge that the dependence of the effect of dihydropyridine Ca agonists BAYK 8644, CGP 28 392 and (-S)202 = 791 on calcium channels on the membrane potential is to a large extent due to the activation and following inactivation of Ca channels "silent" in the control. This effect takes place due to a shift by Ca agonists of the stationary curve of channel activation to hyperpolarization. The absence of stimulus-dependence of the agonist effect and constant time of Ca current reactivation suggest that the agonists bind with resting channels.     

Dicrete zones of electrical connection between Purkinje terminals and muscle fibers in dog ventricles]

Activity of Purkinje terminals (P) and neighbouring muscle (M) fibres (P -- M-pairs) in various regions of dog's right ventricle was recorded. It has been shown that transmission of stimulation from P-to M-fibres is abserved not over all endocardial surface, rather in descrete sites -- zones of P--M-interaction. The zones ellips like with the axes 300X100 micron, they are located relatively far from one another -- at the distance of 800-2000 microns. The total area of the zones equals 5% of endocardial surface. P-M delay is less within the zone of connection of P--M-fibres (4 msec) and greater outside the zone (up to 10 msec).