Temperature-induced variations of blood acid-base status in the lugworm, Arenicola marina (L.): I. In vitro study.

Blood of the lugworm Arenicola marina studied in vitro behaved like a Rosenthal system: when temperature rose, pH decreased and PCO2 increased, whereas [HCO3] remained practically constant. pH values were low whatever the CCO2 and SO2. The temperature coefficient dpH/dt was always significantly different from the mean temperature-induced variations of the neutral pH of pure water between 0 and 30 degrees C. Consequently, the relative alkalinity of the blood, [OH-]/[H+], was very low (range, 1.53-5.06) and increased appreciably with temperature. Calculated changes in the fractional dissociation of protein imidazole groups, alphaIm, were smaller. The very variable buffer power of Arenicola hemoglobin was maximum (beta max) for a strictly defined, temperature-dependent value of pH (pH beta max), suggesting that as yet unidentified ionizable group on the hemoglobin molecule, RH, could be responsible for the pH-dependent changes of blood buffer power in Arenicola. Assuming pK'RH = PH beta max, the calculated fractional dissociation of RH, alpha RH, was constant between 0 and 30 degrees C. The nature of RH is discussed in relation with Reeves's hypothesis concerning the preeminence of protein imidazole groups in the regulation of extra- and intracellular pH.