title: Voltage-dependent modulation of T-type calcium channels by protein tyrosine phosphorylation.
abstract: A T-type Ca2+ channel is expressed during differentiation of the male germ lineage in the mouse and is retained in sperm, where is it activated by contact with the the egg's extracellular matrix and controls sperm acrosomal exocytosis. Here, we examine the regulation of this Ca2+ channel in dissociated spermatogenic cells from the mouse using the whole-cell patch-clamp technique. T currents were enhanced, or facilitated, after strong depolarizations or high frequency stimulation. Voltage-dependent facilitation increased the Ca2+ current by an average of 50%. The same facilitation is produced by antagonists of protein tyrosine kinase activity. Conversely, antagonists of tyrosine phosphatase activity block voltage-dependent facilitation of the current. These data are consistent with the presence of a two-state model, in which T channels are maintained in a low (or zero) conductance state by tonic tyrosine phosphorylation and can be activated to a high conductance state by a tyrosine phosphatase activity. The positive and negative modulation of this channel by the tyrosine phosphorylation state provides a plausible mechanism for the control of sperm activity during the early stages of mammalian fertilization.
authors.affiliation: Department of Anatomy and Cellular Biology, Tufts University School of Medicine, Boston, MA 02111, USA.
authors.forename: C
authors.initials: C
authors.lastname: Arnoult
authors.forename: J R
authors.initials: JR
authors.lastname: Lemos
authors.forename: H M
authors.initials: HM
authors.lastname: Florman
mesh_terms: D000818:Animals; D002109:Caffeic Acids / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004533:Egtazic Acid / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008815:Mice, Inbred Strains; D009570:Nitriles / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D012671:Seminiferous Tubules / Q000502:physiology*; D013087:Spermatids / Q000187:drug effects / Q000502:physiology; D013091:Spermatogenesis; D013997:Time Factors; D020032:Tyrphostins
chemical_list: D002109:Caffeic Acids; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D009570:Nitriles; D020032:Tyrphostins; C079836:tyrphostin 25; C060152:tyrphostin 47; D019000:Phosphotyrosine; D004533:Egtazic Acid; D011505:Protein-Tyrosine Kinases; D017027:Protein Tyrosine Phosphatases