Variations in erythrocyte volume [mean corpuscular volume (MCV)] were evaluated during exercise and heat stress to determine the influence on calculated plasma volume and content changes. The results of this study on 17 men indicate that the human red blood cell can increase, decrease, or remain constant in volume during physical stress depending on the combined interactions of plasma osmolality and blood pH. Shrinking of MCV can occur when the increase in plasma osmolality is larger than 5 mosmol/kg H2O and the blood pH remains within 0.1 pH units of its resting value. Erythrocyte swelling is usually noticed with maximal exercise when the blood pH is less than 7.10, in spite of 20 mosmol/kg H20 increments in plasma osmolality. The regression equations indicate that during 30 min of exercise in a cool environment the plasma shifts calculated by either the hematocrit or the hematocrit + hemoglobin method fall within 1% of each other, but during resting heat exposure the hematocrit technique under-estimates the fluid shift by 2.5-3.0%. Application of these considerations to the calculation of plasma content changes during stress made it clear that the pattern of plasma potassium content is quite different with maximal as compared with submaximal exercise.
Polypyrrole film electrodes are composed of macromolecular electrochemical machines, ions and water. They are considered here as a model of the intracellular matrix of ectothermic muscle cells. The oxidation/reduction responses to the working temperature in aqueous solutions were investigated herein by potential and current steps. Under potentiostatic conditions, rising temperatures stimulate deeper conformational movements of the polymeric chains leading to the exchange of more ions increasing the consumed charge, with the effect that the reaction charge responds and senses the working temperature. Under galvanostatic conditions and higher environmental thermal energies the material potential evolves at lower values during reactions consuming lower electrical energies. At any reaction time, both the consumed reaction energy and the material potential sense the working thermal conditions. Reactions involving molecular machines sense and respond to the working temperature. Similarities with energetic consumptions and sensing responses from muscles in cold‐blooded animals are discussed. A theoretical description is proposed.
Polypyrrole film electrodes are constituted by multielectronic electrochemical molecular machines (every polymeric molecule) counterions and water, mimicking the intracellular matrix of muscular cells. The influence of the electrolyte concentration on the reversible oxidation/reduction of polypyrrole films was studied in NaCl aqueous solutions by consecutive square potential waves. The consumed redox charge and the consumed electrical energy change as a function of the concentration. That means that the extension (the consumed charge) of the reaction involving conformational, or allosteric, movements of the reacting polymeric chains (molecular machines) responds to (senses) the chemical energy of the reaction ambient. A theoretical description of the attained empirical results is presented getting the sensing equations and the concomitant sensitivities. Those results could indicate the origin and nature of the neural signals sent to the brain from biological haptic muscles working by cooperative actuation of the actin-myosin molecular machines driven by chemical reactions and sensing, simultaneously, the fatigue state of the muscle.
For reactions involving molecular machines (artificial or biochemical), the evolution of the reaction energy, or that of any of its components, adapts to and senses the working thermal, chemical, or mechanical conditions. Here, the state of the art and the attained sensing equations of the oxidation/reduction of conducting polymers seen as replicating materials and reactions of the intracellular matrix of functional cells (molecular machines, ions and water) are reviewed. The adapting reaction energy in actuating muscles and other organs can originate the nervous pulses translating its quantitative energetic information (thermal, fatigue state and mechanical) to the brain. Besides, reversible oxidation/reduction charges originate a great asymmetry of the consumed reaction energies, which could explain why evolution has selected and improved the most efficient of the two reactions to drive full asymmetric biological functions such as muscle contraction or the flow of nervous signals. The material reaction drives volume variations and energetic adaptation, two simultaneous functions that have allowed the development of artificial sensing‐muscles postulated to replicate some primitive artificial proprioception.
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