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Journal of Experimental Biology, Vol 148, Issue 1 385-394, Copyright © 1990 by Company of Biologists

JOURNAL ARTICLES

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

TA Heming, CG Vanoye, SE Brown and A Bidani
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.

Cytoplasmic pH (pHi) of haemocytes of bigfin reef squid (Sepioteuthis lessoniana 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) (delta pHi/delta pHe = 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.




© The Company of Biologists Ltd 1990