Mitochondrial inhibitors activate influx of external Ca 2+ in sea urchin sperm

Abstract

Sea urchin sperm have a single mitochondrion which, aside from its main ATP generating function, may regulate motility, intracellular Ca 2+ concentration ([Ca 2+] i) and possibly the acrosome reaction (AR). We have found that acute application of agents that inhibit mitochondrial function via differing mechanisms (CCCP, a proton gradient uncoupler, antimycin, a respiratory chain inhibitor, oligomycin, a mitochondrial ATPase inhibitor and CGP37157, a Na +/Ca 2+ exchange inhibitor) increases [Ca 2+] i with at least two differing profiles. These increases depend on the presence of extracellular Ca 2+, which indicates they involve Ca 2+ uptake and not only mitochondrial Ca 2+ release. The plasma membrane permeation pathways activated by the mitochondrial inhibitors are permeable to Mn 2+. Store-operated Ca 2+ channel (SOC) blockers (Ni 2+, SKF96365 and Gd 2+) and internal-store ATPase inhibitors (thapsigargin and bisphenol) antagonize Ca 2+ influx induced by the mitochondrial inhibitors. The results indicate that the functional status of the sea urchin sperm mitochondrion regulates Ca 2+ entry through SOCs. As neither CCCP nor dicycloexyl carbodiimide (DCCD), another mitochondrial ATPase inhibitor, eliminate the oligomycin induced increase in [Ca 2+] i, apparently oligomycin also has an extra mitochondrial target.