No abstract

Responses to light recorded by means of intracellular microelectrodes in isolated heads kept in oxygenated Ringer solution consist of a slow depolarization. Light adaptation increases the rates of depolarization and repolarization and decreases the amplitude of the response. Qualitatively these changes are similar to those observed in Limulus by Fuortes and Hodgkin. They are rapidly reversible during dark adaptation. In retinula cells of the drone eye a large single spike is recorded superimposed on the rising phase of the slow potential. The spike is a regenerative phenomenon; it can be triggered with electric current and is markedly reduced, sometimes abolished by tetrodotoxin. In rare cases cells were found which responded to light with a train of spikes. This behavior was only found under "unusual" experimental conditions; i.e., towards the end of a long experiment, during impalement, or at the beginning of responses to steps of strongly light-adapted preparations.Experiments performed in different laboratories on invertebrate eyes have shown that responses to light of single visual cells recorded with intracellular microelectrodes have many similarities. In all eyes so far examined the response to a brief flash consists of a slow depolarization which starts with some delay and outlasts considerably the duration of the light pulse. Responses to longer stimuli are composed of two parts, one phasic (the transient), and the other maintained (the plateau). Fuortes and Hodgkin (1) have shown in Limulus that the shape of responses to weak lights or very soon after applying a strong light resembles the shape of responses of a low-pass filter containing several equal stages of exponential delay; furthermore, these authors have found that the modifications of time course and amplitude of visual responses observed in light-adapted eyes can be reproduced in the low-pass filter model by a decrease of the time constant which controls the rate of decay of the response. 855

In the honey bee drone, the decrease in sensitivity to light of a retinula cell exposed to background illumination was found to be accurately reflected by the difference in amplitude between the initial transient depolarization and the lower steady depolarization evoked by the background light. It is shown that both the decrease in sensitivity to light and the accompanying drop in potential from the transient to the plateau can be prevented by injecting EGTA intracellularly. A decrease in duration and amplitude of responses to short test flashes such as observed immediatly after illumination was found to occur too when Ca or Na, but not K, Li, or Mg, were injected into dark-adapted retinula cells. Injection of EGTA into a retinula cell maintained at a steady state of light adaptation, was found to cause an increase in amplitude and duration of the response to a short test flash, thus reproducing the effects of dark adaptation. It is suggested that, in the retina of the honey bee drone, an increase in intracellular calcium concentration plays a central role in light adaptation and that an increase in intracellular sodium concentration, resulting from the influx of sodium ions during the responses to light, could lead to this increase in intracellular free calcium.

Angiotensin-converting enzyme (ACE) was measured in serum of 187 healthy children between the ages six months and 18 years. Results were pooled for five-year age intervals and compared with the reference values for adults that we previously determined [Clin Chem 1986;32:884-6). Results for each age group were also studied as a function of sex. Children had higher ACE activities in serum than did adults (P less than 0.001), but these activities were age-related only from age four to 18 years. Adolescents showed sex-related differences, with higher serum ACE activities in boys than in girls (P less than 0.05). Both sex- and age-related differences may be related to a steroid hormonal regulation of ACE biosynthesis. We also verified that children with sarcoidosis (n = 20) had significantly increased serum ACE activity. Such physiological variations in serum ACE activity must be taken into account for diagnosing sarcoidosis in children, for following the course of the disease, and for evaluating the accuracy of therapy.