Boar sperm plasma membrane calcium selective channels in planar lipid
bilayers sensitivity to bay-k enantiomers and nitrendipine.
Tiwari-Woodruff, Seema K., and Thomas C. Cox.
Department of Physiology, School of Medicine, Southern Illinois University,
Carbondale, Illinois 62901
APStracts 2:0044C, 1995.
Entry of calcium ions through Ca channels is thought to trigger the acrosome
reaction of spermatozoa during fertilization. Antagonists of the L-type Ca
channel are known to prevent the Cai increase and inhibit acrosomal
exocytosis in mammalian sperm. Planar bilayer recordings were used to study
Ca channels incorporated from partially purified boar sperm plasma membranes.
With symmetrical 50 mM NaCl and 100 mM BaCl2 on the cis side, single channel
events consistent with barium flux from cis to trans were observed. These
channels were activated by the dihydropyridine agonist (+/-)Bay-K and blocked
by the antagonist nitrendipine. Sperm Ca channels did not require
depolarization for activation and did not inactivate. The (+/-)Bay-K and (S
-)Bay-K enantiomers increased apparent open time in a dose-dependent (K0.5 =
0.9 and 0.3 [mu]M, respectively) manner. Dihydropyridine antagonists
nitrendipine (K0.5 = 0.5 [mu]M) and (R+)Bay-K (K0.5 = 2.8 [mu]M) decreased
apparent open times. The channels described in this report share some
properties with brain, cardiac and skeletal muscle t-tubule calcium channels
and may be involved in increasing Cai prior to the acrosome reaction.
Received 8 September 1994; accepted in final form 30 November 1994
APS Manuscript Number C0536-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.