Elevation of the intracellular pH activates respiration and motility of sperm of the sea urchin, Strongylocentrotus purpuratus.

The internal pH (pHi) of sperm of the sea urchin, Strongylocentrotus purpuratus, was estimated by measuring the accumulation of the weak bases [14C]methylamine, [14C]diethylamine, or 9-aminoacridine under conditions where cellular respiration was activated or inhibited. When 9-aminoacridine fluorescence measurements are corrected for binding to intracellular components, the pHi estimates agree quantitatively with those obtained from [14C]amine distributions. The pHi of sperm decreased when the intracellular [K+] was elevated above the physiological value of 10 mM, or when the external pH was substantially decreased below the physiological 8.0, or when Na+ was absent from the seawater. At the decreased pHi values, sperm respiration and motility were inhibited; conversely, both respiration and motility increased when the pHi was elevated. Increased respiration occurred whether the pHi was increased by altering the external pH, [K+] or [Na+], or by the addition of NH4Cl to the medium. In all cases, the activation of respiration and motility were linked, suggesting a unitary control mechanism, some possibilities for which are presented.