Emergent studies have recently shown

Emergent studies have recently shown that Sherpas living at high altitude have adaptations that make life at high altitude more compatible. Sherpas are known to have blood Hb concentrations about the same as lowlanders and Han populations [30]. This is different from what happens to lowlanders, Han and even Andean individuals when they adapt at high altitude for they develop a polycythemia that often results in chronic mountain sickness (CMS). Studies have identified in Sherpa populations a mutation in the EGLN1 gene that reduces the effectiveness of hypoxia-inducible factors (HIFs) with regard to their effects on erythropoiesis [31,32]. These are not the only changes associated with Sherpa adaptations at high altitude and there appears to be great interest in studying the various mechanisms involved [33]. Treatment for CMS as well as for acute-mountain disease includes going to a lower altitude (best) and/or the use of acetazolamide [34]. The physiological changes that occur in acute and CMS have yet to be defined as well as the mechanism(s) by which acetazolamide exerts its effect. It is also of interest that cattle raised or kept at high altitude develop a high-altitude sickness often referred to as ‘Brisket Disease’. The characteristics are of course somewhat different from CMS but the genetic basis is related [35]. As with the human disorder the mechanism(s) involved in the origin of brisket disease is unknown. Another group of animals that have members living both at low and high altitudes are the camelidae. This group is comprised of six species, namely, the bactrain, dromedary, llama, alpaca, guañaco and the vicuña. The first two live essentially at sea level (middle east, Africa and Asia) while the others live mainly in the Andean mountains. The Hbs of the high altitude species display higher O2 affinities than those at sea level. In addition, all six species appear to have unique and different amino 974 substitutions in their respective Hbs [29]. Interestingly, the recent cloning of Woolly mammoth Hb found that certain amino acid substitutions on their ß/δ-globin subunits provided at least one indication of how these ancient animals were able to cope/adapt in their Artic-Ice Age environment [36].
Fish without red blood cells For some red cell aficionados, it may come as a surprise to find a group of vertebrates that live without red blood cells! Nevertheless, the group of fish called ‘ice-fish’ (family Channichthyidae), suborder notothenioiri represent a case in point [37]. These ice-fish (some 16 species) live in the Antarctic ocean in waters that have temperatures of −1° to −2 °C. They live on the dissolved O2 in their plasma. It is known that while their genomes contain an altered α-Hb gene [38], that for the ß-subunit is missing. In addition, the fish are protected by anti-freeze molecules in their plasmas (either proteins or glycoproteins) that they have synthesized as a function of their adaptation to their unusual environment [39]. Another change in the adaptation that the ice-fish have made is that while they may have myoglobin in their heart muscle, myoglobin in their skeletal muscles is missing [40].
Red blood cells without band 3 Band 3, the chloride/bicarbonate exchanger is a major membrane constituent of essentially all vertebrate red blood cells. It's structure is known and its physiological function has been well characterized [41]. Its basic function is to provide for the pH control of the blood via the transport of OH− (hydroxal ions) and CO2 between the lungs and the body tissues during rest and exercise. Here again is another surprise when it was discovered that breeds of mice [42] and cows [43] in which Band 3 has been eliminated not only survive but also reproduce. While some altered functions in these animals that result from the loss of Band 3 have been delineated [44] the types of compensatory parameters have yet to be fully defined.