Estimation of intracellular pH in muscle of fishes from different thermal environments

A technique based on homogenisation of rapidly frozen tissue was used to in vestigate the regulation of intracellular pH (pH(i)) in freshwater and mari ne fish from diverse environmental temperatures. The following species were held at ambient temperatures of ca. 1 degrees C (Notothenia coriiceps, Ant arctica), 5 degrees C (Pleuronectes platessa, Myoxocephalus scorpius; North Sea), and 26 degrees C (Oreochromis niloticus, African lakes). The effects of seasonal acclimatisation to 4, 11 and 18 degrees C were also examined i n rainbow trout in the winter, autumn and summer, respectively. Extracellul ar (whole blood) pH (pH(e)) did not follow the constant relative alkalinity relationship, where pH(+) = pOH(-) for any particular temperature, over a range of 1-26 degrees C (overall delta pH(e)/delta T = 0.009 +/- 0.002 U de grees C-1; P < 0.001), apparently being regulated by ionic fluxes and venti lation. Intracellular pH (pH(i)) was also regulated independently of pN(= 0 .5 pK water) in all species of fish examined. The inverse relationship betw een pH(i) and environmental temperature gave an overall delta pH(i)/delta T of -0.010 +/- 0.001 U degrees C-1 (for both white and red muscle) and -0.0 04 +/- 0.093 U degrees C-1 (cardiac muscle). However, between 1 and 11 degr ees C delta pH(i)/delta T was much higher (P < 0.001), -0.022 +/- 0.003 U d egrees C-1 (white muscle) and -0.022 +/- 0.004 U degrees C-1 (red muscle). The possible adaptive roles for these different acid-base responses to envi ronmental temperature variation among tissues and species, and the potentia l difficulties of estimating pH(i). are discussed. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.