Bump Area Research Articles

Single Photon-Evoked Events Of The Ventral Nerve Photoreceptor Cell Of Limulus Facilitation, Adaptation And Dependence Of Lowered External Calcium

Bumps, the elementary excitatory events of the Limulus ventral nerve photo receptor following a weak flash of light were recorded under voltage clamp conditions. The statistical distribution of various bump parameters and their changes caused by weak conditioning pre-illumination are described, and the influence of lowered external Ca2+-concentration together with normal or raised Mg2+-concentration (15 °C). 1) Weak conditioning pre-illumination causes desensitization: the bump current amplitude, bump duration , bump area (current-integral), and the bump latency are diminished, the more, the stronger the conditioning flash, i.e. the light adaptation. Very weak conditioning pre-illumination causes facilitation, expressed by an increase in number and size of the observed bumps. The average bump latency, however, is already shortened under these conditions. 2) Lowering the external Ca2+-concentration from 10 mmol/l to 250 (µmol/1 has its primary effect on the dark -adapted photoreceptor (without substantially reducing the ability for light adaptation ). It causes the following average changes: the amplitudes, durations, current-integrals, and the latencies of current bumps are greatly enlarged and the number of bumps is raised. 3) Raised magnesium concentration from 50 to 100 mmol/l can partially compensate for the lack of calcium ; however, it enhances the effect of calcium deficiency on the latency, i.e. it further enlarges the average latencies. The results can be explained on the basis of our model of bump generation by two assumptions. 1) Lowering the external calcium concentration causes a decrease in the cytosolic Ca2+-level without substantially reducing the intracellular calcium stores from which the light-adapting calcium release is fed. The lowered cytosolic Ca2+-concentration induces an “extra” dark adaptation resulting in greater bumps and more bumps exceeding the threshold of recognition. The bump latency, however, which behaves differently from all other bump parameters, is determined by a separate calcium -dependent reaction where magnesium competes with calcium antagonistically. 2) Facilitation is due to cooperativity of transmitter binding in order to open the ion channels

Observations of Gulf Stream‐induced and wind‐driven upwelling in the Georgia Bight using ocean color and infrared imagery

Ocean color and infrared imagery from aircraft and satellite sensors are combined with in situ measurements of currents, chlorophyll, temperature, salinity, coastal winds, and sea level to study upwelling events in the Georgia Bight where the Gulf Stream and continental shelf waters strongly interact. These interactions were observed over an 8 day period in April 1980 during which five independent upwellings occurred. The upwellings included a nearshore wind‐driven upwelling enhanced by topographic effects, three Gulf Stream filament‐induced upwellings, and what appears to have been a Gulf Stream meander‐induced event. The chlorophyll distributions as inferred from the imagery are found to be reliable tracers which indicate filamentary circulation and propagation and advective routes by which nearshore water moves offshore. The propagation of two of the filaments and the meander are studied in detail using the imagery and mooring array temperature time series. Both techniques yield nearly identical results for the phase speeds of each event. There is evidence that one of the filaments accelerated as it entered into the Charleston Bump area where the Gulf Stream deflects offshore. The other filament exhibited a steady deceleration as it moved past Cape Canaveral and eventually lost any semblance of wave motion. Also included are data from April 1979 which offer corroborating evidence of filamentary structure and circulation. Intercomparisons of field measurements and the Nimbus 7/coastal zone color scanner estimates of surface pigment concentrations show excellent agreement over the range of 0.1–7.0 mg/m3.