A CYTOSOLIC SPERM FACTOR TRIGGERS CALCIUM OSCILLATIONS IN RAT HEPATOCYTES

Previously it has been shown that injecting a cytosolic sperm protein factor into mammalian eggs induces sustained repetitive transients of cytosolic free Ca2+ ([Ca2+](i)), or [Ca2+](i) oscillations [Swann (199 0) Development 110, 1295-1302]. These sperm-factor (SF)-induced [Ca2+] (i) oscillations are similar to those seen at fertilization. Here we d emonstrate that injecting the same cytosolic extracts of mammalian spe rm into single rat hepatocytes induces a series of [Ca2+](i) oscillati ons, as measured by aequorin luminescence. SF injection into hepatocyt es induced [Ca2+](i) oscillations that were of longer duration, lower frequency and greater amplitude than those seen with the Ins(1,4,5)P-3 -generating agonist phenylephrine. The SF-induced [Ca2+](i) responses appeared to be due to internal release of Ca2+, since transients could occur in Ca2+-free media. Addition of the phorbol ester phorbol 12,13 -dibutyrate (PDBu) at low concentrations did not inhibit the SF-induce d [Ca2+](i) oscillations; high concentrations of PDBu led to a sustain ed increase in [Ca2+](i) concentrations. These data demonstrate that s perm contain a protein factor capable of inducing a characteristic ser ies of [Ca2+](i) oscillations in a somatic cell, the hepatocyte. Along with previous observations in dorsal root ganglion neurons, the data suggest a widespread efficacy of the factor in triggering Ca2+ oscilla tions.