Charlotte P. Mangum

The effects of environmental variables on the heart rates of invertebrates

1. 1. The effects of temperature, salinity and declining O2 on the heart rates of nine species representing four animal phyla have been investigated in relation to other respiratory paramters. 2. 2. The effect of temperature on heart rate is at least the same as, and often greater than, the effect of temperature on O2 consumption, thus providing no evidence that adaptations of the cardiovascular system facilitate metabolic compensations for a temperature change. 3. 3. Responses to reduced acclimation salinity are very diverse among the various species, permitting no general conclusions about the role of the cardiovascular system in adaptations to estuarine habitats. 4. 4. At low PO2 the typical response is bradycardia, which is especially notable in species with a high capacity for anaerobic metabolism. Compensatory tachycardia, the expected response in vertebrates, is very rare in other animal groups. 5. 5. Estimates of cardiac output from these data generally agree with those obtained according to the Fick principle from blood gas tensions. 6. 6. The estimates of cardiac output are evaluated in terms of body size, temperature and the design of cardiac muscle, which is fundamentally different in various animal phyla.

The function of coelomic cell hemoglobin in the polychaete Glycera dibranchiata

Abstract 1. 1. The annelid bloodworm Glycera dibranchiata contains large quantities of hemoglobin in metabolically active coelomic cells. 2. 2. The quantitative participation of hemoglobin in aerobic respiration by the animal is detectable, but it is not very great. 3. 3. The substance apparently functions in oxygen transport at intermediate and high pO2s; at very low pO2s both circulation and aerobic respiration are shut down. 4. 4. It is also likely that the substance functions as an oxygen storage compound, both during normal pauses in ventilation and at low tide when no ventilation occurs. 5. 5. Dissolved extracts of bloodworm hemoglobin consist of two components which are clearly separable on the basis of physiological properties as well as molecular weight, a light fraction with a higher oxygen affinity and a heavy fraction with a lower oxygen affinity.

Respiratory Responses of the Blue Crab Callinectes sapidus to Long-Term Hypoxia

Blue crabs (Callinectes sapidus) were held in hypoxic (50-55 mm Hg) water for 7-25 days. Postbranchial blood PO2 fell by about 80% within 24 h and then remained unchanged. Postbranchial blood total CO2 increased within 24 h and remained elevated for the duration of the experiment. There was no change in postbranchial blood pH, osmolality, or Cl. Lactate, urate, and Ca+2 all raise the O2 affinity of blue crab hemocyanin; by 25 days, blood lactate and urate had risen slightly, but Ca+2 had increased dramatically. Hemocyanin concentration had also increased by 25 days. At both 7 and 25 days there was an intrinsic increase in hemocyanin-O2 affinity and a change in subunit composition. The highly adaptive homotropic change is believed to be due to an attendant shift in the proportions of two of the three variable monomeric hemocyanin subunits. Thus, both heterotropic and homotropic adaptations enhance blood oxygenation at the gill during long-term hypoxia.

THE INFLUENCE OF INORGANIC IONS AND ACCLIMATION SALINITY ON HEMOCYANIN-OXYGEN BINDING IN THE BLUE CRAB CALLINECTES SAPIDUS

The effects of salinity changes on the oxygen binding properties of hemocyanin have been examined in the blue crab Callinectes sapidus. Oxygen affinity increases measurably with increases in Ca+2, Mg+2 or Na+ but, within the physiological range, not K+. Unlike its large and specific influence on other arthropod hemocyanins, Cl- has little or no effect. Ca+2, alone and in physiological concentrations, restores oxygen affinity to the level observed in a complete physiological saline. Ca+2 also restores the Bohr shift to the physiological level. Physiological variation in inorganic ions (or pH) does not affect the cooperativity of oxygen binding.Physiological variation in Ca+2 explains only a minor fraction of the actual change in oxygen affinity that accompanies acclimation to a new salinity. The aclimation, which occurs within 8 days, requires a non-dialyzable factor in the blood. The non-dialyzability of the factor and the previous reports of a large increase in blood protein levels at low salinity might ...

The pH of body fluids of marine invertebrates

Abstract 1. 1. The pH of anaerobically handled blood and other body fluids from seventeen species of marine invertebrates was measured at temperatures to which the animals were acclimated. 2. 2. At midsummer temperatures the blood pH of the holothurian Thyone briareus is considerably lower than the mammalian value of 7·4, which has been widely assumed to prevail in poikilothermic animals. Values in a number of decapod crustaceans and gastropod molluscs are considerably higher than 7·4. 3. 3. These values would be expected to increase in other seasons.

Temperature sensitivity of active and resting metabolism in a polychaetous annelid.

Abstract 1. 1. Temperature coefficients have been computed for oxygen consumption rates measured during active and resting periods of the rhytmic activity cycle of a polychaetous annelid. 2. 2. Neither active nor resting metabolism of acclimated worms shows perfect thermal compensation. Instead, Q 10 values for active and resting metabolism are similar to one another, and also to values from previous reports in which the distinction is not made.

The relationship between subunit composition and O2 binding of blue crab hemocyanin

Hemocyanin-O2 affinity differs in estuarine and seaside populations of the blue crab Callinectes sapidus. The difference, which is adaptive, is accompanied by different proportions of the six subunits that make up the native hemocyanin polymers. When the hemocyanins are dissociated and separated by alkaline electrophoresis, six subunits can be resolved in most estuarine individuals but two of the six are either present in low concentrations in or absent from most seaside individuals. A third subunit is also variable but the variation is not clearly correlated with locality. O2 binding measurements of Hcs with the two major wild phenotypes but collected at the same locality reproduce the difference between the natural populations. Measurements on several intermediate phenotypes suggest that the variation of one of the subunits is more important physiologically than variation of the other two.

THE CO2 SENSITIVITY OF THE HEMOCYANINS AND ITS RELATIONSHIP TO Cl- SENSITIVITY

The effect of CO2 on hemocyanin-oxygen binding is not generally related to the effect of Cl-. Some hemocyanins respond to both and some to either one alone. The direction of the responses of O2 affinity of the various hemocyanins to CO2 is poorly correlated with the direction of responses to other effectors. The influence of CO2 on Busycon and Limulus hemocyanins reaches its maximum at high pH. Since the effect can be abolished by restoring divalent cation activities to the control levels prior to the addition of CO2, we suggest that the effect is not specific but rather indirect, by the pairing of the allosteric effectors Ca+2 and Mg+2 with the CO2 anions. In contrast the effect of CO2 on crustacean hemocyanins is greaterat low pH and it can be enhanced by maintaining HCO3- levels within narrow limits and permitting PCO2 to vary by a large factor. This finding suggests that the effective species is molecular CO2. While a influences only oxygen affinity, CO2 may influence cooperativity as well. Indifferen...

The role of coelomic hemerythrin in the sipunculid worm Phascolopis gouldi

Abstract 1. 1. Under normoxic conditions in the water column the sipunculid worm Phascolopsis gouldi maintains a burrow pO2 of 77–81 mm Hg and a coelomic fluid pO2 of 5–8 mm Hg. 2. 2. At 23°C the oxygen affinity of hemerythrin in intact coelomic cells is 5–6 mm Hg and the operating range is 0–25 mm Hg. These quantities are significantly reduced at 10°C. 3. 3. The oxygen affinity of hemerythrin in cells is significantly lower than that of extracts, and oxygen release at higher partial pressures is significantly enhanced.

The function of hemoglobin in the arcid clam Noetia ponderosa--I. Oxygenation in vitro and in vivo.

Abstract 1. The mol. wt of the hemoglobin of the arcid clam Noetia ponderosa estimated on a calibrated gel column is 34,500, suggesting a dimeric molecule. 2. The oxygen affinity (P50) of hemoglobin in intact cells in the pH range 6·6–7·4 is 5·30 mm Hg at 10°C and 6·25 mm Hg at 23°C. 3. Two phases of oxygen equilibrium curves can be detected, each with a significantly different Hill coefficient (n). The slope of the curve at lower oxygenation levels is slightly less than that at higher oxygenation levels. 4. Total oxygen content and PO2 of the blood of animals exposed to various oxygen conditions indicate that substantial changes in oxygenation occur at environmental PO2s above 70 mm Hg, which are typical of the habitat. The measurements indicate that the blood from clams exposed to very low oxygen levels still contains detectable amounts of oxygen.