CALCIUM IONS AND CONTROL OF THE MOTILITY OF SEA URCHIN SPERMATOZOA

Abstract

Summary. Both excess and insufficient calcium ions in the medium adversely affected the swimming performance of sea urchin spermatozoa. Sperm cells suspended in calcium-free artificial sea water swam at less than half the speed of those suspended in artificial sea water containing the optimum of 9 mmol CaCl2/1. Excess Ca2+ added to natural sea water decreased motility by 20 % at 36 mm (four times the normal amount) while the same amount of CaCl2 in artificial sea water depressed motility by 45%. The chelating agent, EGTA, caused greater depression than equivalent amounts of EDTA, though at millimolar concentration or higher both caused complete cessation of motility with the flagella in a rigidly extended position. If LaCl3 was added to artificial sea water containing 9 mm-CaCl2, it caused an even greater depression of motility. The effects were detectable at 50 nmol LaCl3/1 and complete inhibition occurred at 20 μmol/1. The flagella ceased beating in a coiled seemingly `relaxed' state. Sperm motility appears to require maintenance of Ca2+ gradients, reversible sequestration and release of Ca2+, and Ca2+-dependent metabolic regulation of the flagellar contractile system.