Abstract
The relationship between the plasma membrane potential and activation of sperm motility and respiration, or induction of the acrosome reaction, was explored in sperm of the sea urchin Strongylocentrotus purpuratus. Plasma and mitochondrial membrane potentials were estimated by measuring the uptake of [14C]thiocyanate ( [14C]SCN-) and [3H]tetraphenylphosphonium ( [3H]TPP+) in intact sperm and sperm made permeant with digitonin. Mitochondrial potentials up to-185 mV were found, consistent with data for TPP+ uptake into mitochondria from other cell types. Values for TPP+ uptake corrected for mitochondrial accumulation and estimates of SCN- uptake both indicated that the plasma membrane potential was about -30 mV for actively respiring sperm in seawater and about -60 mV for quiescent sperm in Na+-free seawater. Activation of sperm motility and respiration induced by Na+ increased the intracellular pH and caused a depolarization of both the plasma membrane and mitochondrial potentials. However, membrane potential depolarization did not occur when the activation was induced by increased extracellular pH or by the peptide speract, although activation was always linked to increased intracellular pH. The acrosome reaction, on the other hand, was always associated with sperm plasma membrane potential depolarization, whether it was induced by the physiological effector from the egg surface or by several artificial triggering regimens. Thus, activation of respiration and motility is primarily controlled by increased intracellular pH (Christen, R., Schackmann, R. W., and Shapiro, B. M. (1982) J. Biol. Chem. 257, 14881-14890), whereas the acrosome reaction also requires depolarization of the plasma membrane potential.
Highlights
The relationship between the plasma membrane potential and activation of sperm motility and respiration, or induction of the acrosome reaction, was explored in sperm of the sea urchin Strongylocentrotus purpuratus
When appropriate correctiownsere made for mitochondrial accumulation of TPP+,we found a plasma membrane potential of-27mV in ASW, in accord with measurements using SCN (Table I)
Toascertain whether pHi was coupled directly tothe change in plasma membrane potential upon addition of Na+, we explored the inter-relationships of these two changes in greater detail
Summary
The lipophilic ions SCN, TPP, and TPMP have been used to evaluate membrane potentials in intact eukaryotic cells [14, 16,30]. It is clear that motility and respiration are not that follow it This depolarization reflects rapid changes in directly regulated by the plasma membrane potential, for the biochemical properties of the sperm plasma membrane. It sperm are motile and respire at either low or high negative is accompanied by a substantial increase in Ca2+influx, and plasma membrane potentials (Fig. 6 and Table 11) provided we are presently exploring the possibility that Ca2+channels that the pHi is sufficiently high for the dynein ATPase to of the sperm plasma membrane are opened by the plasma function [18]. Lipophilic ions appear to collapse the mitochondrial potential in intact
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