Adult fast myosin pattern and Ca2+-induced slow myosin pattern in primary skeletal muscle culture

A primary muscle cell culture derived from newborn rabbit muscle and growing on microcarriers in suspension was established. When cultured for several weeks, the myotubes in this model develop the completely adult pattern of fast myosin light and heavy chains. When Ca2+ ionophore is added to the culture medium on day 11, raising intracellular [Ca2+] about 10-fold, the myotubes develop to exhibit properties of an adult slow muscle by day 30, expressing slow myosin light as well as heavy chains, elevated citrate synthase, and reduced lactate dehydrogenase. The remarkable plasticity of these myotubes becomes apparent, when 8 days after withdrawal of the ionophore a marked slow-to-fast transition, as judged from the expression of isomyosins and metabolic enzymes, occurs.

Hypoxic incubation leads to concerted changes of carbonic anhydrase activity and 2.3 DPG concentration of chick embryo red cells

Red cell carbonic anhydrase activity, 2.3 DPG concentration, and activities of three key enzymes controlling DPG metabolism (PK, PFK and DPGM) were measured in normoxic and hypoxic (incubation in 13.5% O2) chick embryos. In normoxia 2.3 DPG concentration and carbonic anhydrase activity begin to increase by the third week of incubation. Hypoxia induces a rise of 2.3 DPG concentration and carbonic anhydrase activity by Day 8 of development, i.e., 1 week earlier. Since during normal development chick embryos become hypoxic in the third week of incubation, the results suggest that PO2 has a controlling influence on the timing of differentiation events of definitive embryonic red cells.

Organic phosphates increase the solubility of avian haemoglobin D and embryonic chicken haemoglobin

The isolated minor haemoglobin fractions (haemoglobin D) of ostrich, chicken and duck haemoglobin, which constitute about 30% of total intracellular haemoglobin, form crystalline aggregates upon deoxygenation at physiological temperature, ionic strength and pH and at haemoglobin concentrations even well below those present in the red cell. The aggregation is reversed by oxygenation, and can be inhibited by addition of organic phosphates or the corresponding major haemoglobin fraction in a stoichiometric ratio of 1:1. Embryonic haemoglobin from chicken has similar characteristics with respect to its solubility. The results indicate close functional homology of alpha D and embryonic pi-chains as well as a novel role for organic phosphates in the regulation of haemoglobin function.

Effects of hypoxia on oxygen affinity, hemoglobin pattern, and blood volume of early chicken embryos

We have investigated the influence of hypoxia (13.5% O2) on the oxygen affinity, hemoglobin pattern, and blood volume of chicken embryos. Data were collected between 4 and 9 days of incubation. It was found that the transition from embryonic to adult hemoglobin starts earlier in hypoxic embryos, due to a premature appearance of definitive red cells in the circulation. Blood oxygen capacity and total blood volume (related to embryonic weight) were not different from the controls. However, hypoxic embryos weighing more than 0.1-0.2 g have a significantly increased oxygen affinity (and decreased red cell adenosine 5'-triphosphate concentration). The higher O2 affinity partly compensates for the adverse effects of the lowered environmental PO2. In hypoxic embryos younger than 6 days, the Bohr effect is drastically increased, which allows a better oxygen extraction. Thus, the chicken embryo seems to be able to develop adaptive changes of blood O2 transport during hypoxia. The results support the view that the particular ontogenetic pattern of O2 affinity changes seen in avian or mammalian embryos arose from the need to adapt to the steadily changing conditions for O2 uptake.

Functional properties of embryonic chicken hemoglobins

We have investigated the O2-binding properties of the four embryonic hemoglobins (Hb P, Hb P', Hb M, and Hb E) under various conditions and compared the results with measurements on early embryonic chicken blood between 3 and 6 days of incubation. The O2-binding curve of embryonic blood is polyphasic. Hill's coefficient changes continuously from less than or equal to 1 at low O2 saturation to a value of approximately equal to 8 in the upper saturation range. The high cooperativity is coupled with a very low O2 affinity in the middle range of the O2-binding curve. Between 3 and 6 days of development the O2 affinity and cooperativity as well as the Bohr effect of embryonic blood change drastically, without corresponding alterations of the hemoglobin pattern or ATP concentration. The functional properties of the embryonic blood cannot be simulated with the isolated embryonic hemoglobins at physiological concentrations of ATP, hemoglobin, and protons. On the other hand, freshly prepared hemolysate shows the same functional pattern as the embryonic blood. The results suggest that embryonic red blood cells may contain other low-molecular-weight substances that reduce the O2 affinity and increase the cooperativity of the major embryonic hemoglobins, Hb P and Hb P', presumably by promoting tetramer-tetramer aggregation.

Oxygen-linked CO2 transport in sheep blood

We have analyzed oxygen-linked carbamate formation in sheep hemoglobin B by measuring a) the effect of CO2 on oxygen affinity and Bohr effect in red cell suspensions and dilute (1.3 mM Hb4) and concentrated (5 mM Hb4) hemoglobin solutions at 37 degrees C and b) CO2 binding curves of deoxygenated and oxygenated whole blood and hemoglobin solutions, respectively, at the same temperature. In the presence of CO2 both the Bohr effect and oxygen affinity were significantly lower in 1.3-mM Hb4 solutions than in either red cell suspensions or 5-mM Hb4 solutions, while in the absence of CO2 Bohr effect and oxygen affinity did not differ significantly in those preparations. Likewise, the fraction of oxygen-linked carbamate obtained from CO2 binding curves was found to be higher in 1.3-mM Hb4 (0.156 M HbCO2/M HbO2) solutions than in 5-mM Hb4 solutions (0.12 M HbCO2/M HbO2) at pH 7.2. We conclude that hemoglobin concentration affects formation of oxygen-linked carbamate. Total oxygen-linked CO2 in sheep whole blood amounted to 0.18 M CO2/M O2 of which 70% is oxygen-linked carbamate. Assuming a respiratory quotient of 0.85, the contribution of oxygen-linked CO2 to carbon dioxide exchange in sheep blood was computed to be 21%.