Cytoplasmic pH recovery in acid-loaded haemocytes of squid (Sepioteuthis lessoniana) Available to Purchase

Cytoplasmic pH (pHi) of haemocytes of bigfin reef squid (Sepioteuthis lesso-niana Lesson) was determined with the fluorescent probe, 2′,7′-biscarboxyethyl-5,6-carboxyfluorescein (BCECF). The pHi of haemocytes suspended in nominally HCO₃⁻-free medium (extracellular pH 7.4) averaged (±S.E.) 7.32±0.02. Intracellular pH was independent of external Na⁺ concentration and varied only slightly with changes in extracellular pH (pHe) (ΔpHi/ΔpHe=0.16 over the pHe range 6.8–7.8). Addition of weak acids (sodium propionate, potassium acetate) to haemocyte suspensions resulted in a rapid decrease in pHi. Haemocyte pHi then recovered with an average half-time of 3–4 min. Recovery of pHi was independent of external Na⁺ concentration and insensitive to amiloride, but was abolished by N-ethylmaleimide (NEM). These results argue against the involvement of plasma membrane Na⁺/H⁺ exchange or other Na⁺-dependent transport mechanisms in the pHi recovery of acid-loaded haemocytes. The results suggest that there is an NEM-sensitive proton extrusion mechanism in the plasma membrane of squid haemocytes.