Relationships between hormone-induced calcium release and 86rubidium uptake stimulation in starfish oocytes.
86Rubidium+ uptake, but not 86Rubidium efflux, is strongly stimulated after addition of the meiosis inducing hormone 1-methyladenine (1-MeAde) to prophase blocked oocytes of the starfish Marthasterias glacialis. This stimulation is a transient process which does not require the continuous presence of 1-MeAde and is elicited within 1 minute of contact. 1-MeAde and its biologically active structural analogs fully stimulate Rb+ uptake at concentrations which are about two orders of magnitude lower than those required to trigger meiosis reinitiation but which already release underthreshold levels of Ca2+ from the inner part of the plasma membrane. External Ca2+ concentrations effective in triggering meiosis reinitiation also stimulate Rb+ influx, while drugs like D600, theophyllin and caffein which suppress the hormone induced Ca2+ release, simultaneously preclude the stimulation of Rb+ uptake. Dithiothreitol (DTT) which mimicks 1-MeAde action in releasing Ca2+ and inducing meiosis acts both on the efflux and on active and passive Rb+ influxes. Ouabain, the classical inhibitor of the Na+, K+ pump does not preclude meiosis reinitiation under the influence of 1-MeAde, its agonists of mimetics. It suppresses the active component of Rb+ uptake both in control or stimulate oocytes. When applied only in preincubation before starting the hormone treatment, it cannot however inhibit the stimulation of Rb+ uptake, while basal pump inhibition is preserved. These results demonstrate that stimulation of the active Rb+ or K+ transport is not indispensable to meiosis reinitiation. They suggest moreover that the hormone induced Ca2+ release from the plasma membrane may be responsible for unmasking new ouabain sensitive transport sites.
D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D005260:Female; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010063:Ovum / Q000378:metabolism*; D011418:Prophase; D012413:Rubidium / Q000378:metabolism*; D013215:Starfish / Q000378:metabolism
D010042:Ouabain; D000225:Adenine; D012413:Rubidium; D002118:Calcium