Control of the low voltage-activated calcium channel of mouse sperm by egg ZP3 and by membrane hyperpolarization during capacitation.

Sperm adhesion to egg zonae pellucidae initiates sperm acrosome reactions, an exocytotic event that is an early step during fertilization. Previously, it was suggested that zona pellucida-evoked Ca2+ entry into sperm through low voltage-activated Ca2+ channels is an essential step in acrosome reactions, based on the inhibitory effects of Ca2+ channel antagonists. However, analysis of this channel is limited by the inability to apply electrophysiological methods directly to sperm. In this report, optical methods of determining membrane potential and internal Ca2+ levels were used to demonstrate that (i) contact with zonae pellucidae activates a transient Ca2+ response in sperm that has a time course and antagonist sensitivity anticipated of low voltage-activated Ca2+ channels; (ii) these channels are unavailable for opening in uncapacitated sperm because of voltage-dependent, steady state inactivation; (iii) membrane hyperpolarization during sperm capacitation is sufficient to recruit channels into a closed state, from which they are available for opening during fertilization; and (iv) channel conductance state may be a factor in determines the efficacy with which channel antagonists inhibit fertilization. This study provides evidence for the activation of sperm Ca2+ channels during gamete adhesion and offers a mechanism that may account for aspects of the regulation of sperm fertility during capacitation through the control of channel availability. Finally, these results suggest that channel conductance state may be a central feature in the design of channel antagonists that inhibit sperm function.

Alz-50 and MC-1, a new monoclonal antibody raised to paired helical filaments, recognize conformational epitopes on recombinant tau.

Using a series of recombinant tau and FAC1 mutant proteins, this study demonstrates by Western and dot blot analysis that 1) shared epitopes between tau and FAC1 are responsible for Alz-50 binding; 2) Alz-50 reactivity is dependent on two discontinuous portions of the tau molecule; 3) Alz-50 reactivity is most likely the result of a conformational alteration of tau monomers in Alzheimer's disease; and 4) the epitope for MC-1, a novel monoclonal antibody, maps to similar regions of tau but does not react with FAC1. These data raise questions regarding previous studies which have suggested that tau lacks a specific conformation and illustrate the utility of the Alz-50 and MC-1 antibodies in recognizing a distinct pathological conformation of the tau molecule in Alzheimer's disease.