Inwardly rectifying K(+) channels in spermatogenic cells: functional expression and implication in sperm capacitation.
To fertilize, mammalian sperm must complete a maturational process called capacitation. It is thought that the membrane potential of sperm hyperpolarizes during capacitation, possibly due to the opening of K(+) channels, but electrophysiological evidence is lacking. In this report, using patch-clamp recordings obtained from isolated mouse spermatogenic cells we document the presence of a novel K(+)-selective inwardly rectifying current. Macroscopic current activated at membrane potentials below the equilibrium potential for K(+) and its magnitude was dependent on the external K(+) concentration. The channels selected K(+) over other monovalent cations. Current was virtually absent when external K(+) was replaced with Na(+) or N-methyl-D-glucamine. Addition of Cs(+) or Ba(2+) (IC(50) of approximately 15 microM) to the external solution effectively blocked K(+) current. Dialyzing the cells with a Mg(2+)-free solution did not affect channel activity. Cytosolic acidification reversibly inhibited the current. We verified that the resting membrane potential of mouse sperm changed from -52 +/- 6 to -66 +/- 9 mV during capacitation in vitro. Notably, application of 0.3-1 mM Ba(2+) during capacitation prevented this hyperpolarization and decreased the subsequent exocytotic response to zona pellucida. A mechanism is proposed whereby opening of inwardly rectifying K(+) channels may produce hyperpolarization under physiological conditions and contribute to the cellular changes that give rise to the capacitated state in mature sperm.
Muñoz-Garay
C
C
Departamento de Genética y Fisiología Molecular, Instituto de Biotecnología, UNAM, Cuernavaca, México.
De la Vega-Beltrán
J L
JL
Delgado
R
R
Labarca
P
P
Felix
R
R
Darszon
A
A
D000818:Animals; D001464:Barium / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D002586:Cesium / Q000378:metabolism; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D008297:Male; D051379:Mice; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D013075:Sperm Capacitation / Q000502:physiology*; D013091:Spermatogenesis / Q000502:physiology*
D002412:Cations; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D002586:Cesium; D001464:Barium; D011188:Potassium