Labarca P, Santi C, Zapata O, Morales E, Beltr'an C, Li'evano A, Darszon A
Centro de Estudios Cient'ificos de Santiago, Universidad de Chile, Santiago, Chile.
Dev Biol. 1996 Mar 15;174(2):271-80. doi: 10.1006/dbio.1996.0072.
Ion channels are deeply involved in sperm physiology. In sea urchin sperm cyclic nucleotide levels increase during quimotaxis and in the acrosome reaction (AR). Although cyclic nucleotides are second messengers known to directly or indirectly modulate ion channels, it is not clear how they modulate sperm responses to the egg outer layer. Here, we describe a cAMP regulated K+-selective channel from sea urchin sperm plasma membranes fused into planar bilayers that may have a role during sea urchin sperm quimotaxis and/or the AR. Its single channel conductance in 100 mM KCl is 103 pS. In bi-ionic experiments, the channel displayed a K+/Na+ permeability ratio (PK+/PNa+) of approximately 5. Thus, in sea water its reversal potential would be approximately -13 mV and channel opening would depolarize spermatozoa. The channel has low open probability (Po = 0.8 +/- 0.2% at 0 mV applied voltage) and weak voltage dependence. Channel activity is reversibly up-regulated by cAMP in the cis bilayer side, but not by cGMP. This modulation followed a single Langmuir isotherm with an apparent kd of 200 microM. At this concentration the channel open probability at 0 mV increased up to 11- fold. TEA+ blocked the channel only from the trans side. Also Ba2+ in trans blocked the channel in a voltage-dependent manner.
离子通道与精子生理密切相关。在海胆精子中，趋化性和顶体反应（AR）过程中环状核苷酸水平会升高。尽管环状核苷酸作为第二信使可直接或间接调节离子通道，但目前尚不清楚它们如何调节精子对卵外层的反应。在此，我们描述了一种来自海胆精子质膜的受cAMP调节的钾离子选择性通道，该通道融合到平面双层膜中，可能在海胆精子趋化性和/或顶体反应中发挥作用。其在100 mM KCl中的单通道电导为103 pS。在双离子实验中，该通道的钾离子/钠离子通透率（PK+/PNa+）约为5。因此，在海水中其反转电位约为 -13 mV，通道开放会使精子去极化。该通道开放概率较低（在0 mV施加电压下Po = 0.8 +/- 0.2%）且电压依赖性较弱。通道活性在顺式双层膜侧可被cAMP可逆地上调，但不能被cGMP上调。这种调节遵循单一的朗缪尔等温线，表观解离常数kd为200 microM。在此浓度下，0 mV时通道开放概率可增加至11倍。TEA+仅从反式侧阻断该通道。此外，反式的Ba2+以电压依赖性方式阻断该通道。
