Discontinuous respiration in diapausing pupae of Cecropia silkworms was monitored by means of several electronic methods, including recording changes in haemocoelic pressure, monitoring respiratory movements by strain-gauge sensors and nanorespirographic recording of O2 consumption and CO2 output. It appears that, in contrast to previous concepts of stereotypic discontinuous respiration cycles (DGC) driven by accumulation of gaseous CO2 in the body, the new results indicate that CO2 remains dissolved in liquid carbonate buffers during interburst periods. In other words, there is no accumulation of gaseous CO2 within the air filled tracheal space between the bursts. The bursts of CO2 are caused by homeostatically regulated enzymatic hydration by carbonic anhydrase of metabolically produced carbonic acid. The chemically produced gaseous CO2 was exhaled mainly by a bulk outflow through selectively opened or pulsating spiracles. The output of CO2 was enhanced by actively regulated, unidirectional ventilation. The deep depressions in haemocoelic pressure, caused by permanent closure of all spiracular valves for long periods, appeared to be a specific feature of diapausing saturniid pupae. Physiologically, it has circulatory, not respiratory functions. The original definition of spiracular "fluttering" resulted from a misinterpretation of previously unknown extracardiac pulsations in haemocoelic pressure. The coordinated pulsation of the spiracular valves with extracardiac pulsations produce a very efficient, unidirectional ventilation of the whole tracheal system. According to the new results, the discontinuous respiration cycles of diapausing Cecropia pupae can be briefly described as follows: (1) Spiracular valves are kept permanently closed during the periods of deep depressions, they remain closed for some 99% of the time with occasional snap opening (passive inspirations) during prolonged interburst periods and more than 50% closed during the bursts; (2) During the long interburst periods, CO2 is retained in liquid carbonate buffers, while the relatively high (after the burst) or low (toward the next burst) rate of O2 consumption creates an internal vacuum, which is homeostatically compensated for by the snap-opening of one or just a few spiracular valves (passive suction inspirations); (3) The CO2 gas, produced enzymatically by carbonic anhydrase, enters the air filled tracheal system and leaves the body by diffusion, a bulk outflow, or actively regulated unidirectional ventilation ("fluttering" spiracles). The selective advantage of this actively regulated respiratory system for water retention in pupae is discussed.
1_The respiratory metabolism of different polyphenic forms of the pea aphid, including wingless and winged asexual females (virginoparae), sexual females (oviparae) and winged or wingless adult males, was investigated using a micro-respirographic method. The records revealed sub-nanoliter amounts per min of O2 consumption or CO2 output. Respiratory metabolism of individuals was monitored for 3 to7 h after removal of the aphid from the food plant. Most of the recordings were for relatively large (3.5 mg), wingless asexual females (virginoparae). These aphids exhibited a continuous and very regular respiratory gas exchange (example: specimen of 3.5 mg body mass consumed 180 nl of O2 per min; released simultaneously 300 nl CO2 per min; = standard metabolic rate of 3085 µl O2 / g / h; R.Q. = 1.66). This continuous pattern of respiration occurred only when the aphids were kept at relatively high humidity. By contrast, aphids of various seasonal forms exhibited discontinuous respiratory gas exchange when kept in relatively dry air (atmospheric, room conditions). These patterns can be briefly described as follows: (a) Short and rather small micro-cycles of CO2 emission, manifested usually by the sudden expiration of 60–120 nl of CO2 once every 5 min; (b) Larger bursts of 240–480 nl of CO2 with a periodicity of one hour; (c) Enormously large, discontinuous bursts of 10–14 µl CO2, duration 10–30 min, repeated with a periodicity of several hours. There was no constant pattern of diffusive CO2 emission (DGC). The aphids exhibited a pattern of CO2 release that was appropriate for the external conditions, such as temperature and humidity, and internal physiological conditions such as metabolic activity, availability of reserve substances (carbohydrate, lipid) and water. Certain stages (wingless virginoparae) exhaled volumes of CO2 greatly in excess of their O2 consumption (R.Q. over 1.5)., 2_Sudden exhalations of CO2 from the body were a consequence of a bulk production and outflow of CO2 and not due to the diffusion of CO2 previously accumulated within the tracheal system. Due to their generally high metabolic activity (1142 to 6780 µl O2 / g / h), aphid tissue and organs produced relatively large amounts of metabolically formed carbonic acid. The resulting respiratory acidaemia was moderated by outbursts of gaseous CO2, liberated from liquid carbonate buffers by a regulatory mechanism based on enzymatic hydration and neutralization of carbonic acid by discontinuous formation of gaseous CO2., Karel Sláma, Pavel Jedlička., and Obsahuje seznam literatury