Introduction

Most measurements of the effects of acid toxicity on aquatic animals concentrate upon changes in body fluid pH and the flux of ions between water and blood. One problem posed by a low blood pH is the potential acidification of the tissues which could cause undesirable deviation from the optimum pH of intracellular enzymes. This chapter examines the techniques and results of investigations into the regulation of intracellular pH (pHi).

Relatively little is known about pHi in most animals, experiments being so far generally confined to those with large neurones. This is because until recently the only way of following pHi over long periods was with pH-sensitive microelectrodes. This method is still the best, but requires both skill and a large cell. For small cells fluorescent dyes are very promising.

In this chapter I will describe some of the evidence on which the present understanding of pHi regulatory mechanisms in snail, crayfish and leech neurones is based. I will confine this chapter to these preparations because they are reasonably typical, and I lack the space for a full review. I will then consider the effects of external acidification before concluding that maintenance of a constant pHi depends very much on a constant external pH. For a detailed review of intracellular pH, see Roos & Boron (1981), but for shorter and more recent accounts of the subject see Thomas (1984, 1986).