Patch clamp studies of human sperm under physiological ionic conditions reveal three functionally and pharmacologically distinct cation channels.
Whilst fertilizing capacity depends upon a K(+) conductance (GK) that allows the spermatozoon membrane potential (Vm) to be held at a negative value, the characteristics of this conductance in human sperm are virtually unknown. We therefore studied the biophysical/pharmacological properties of the K(+) conductance in spermatozoa from normal donors held under voltage/current clamp in the whole cell recording configuration. Our standard recording conditions were designed to maintain quasi-physiological, Na(+), K(+) and Cl(-) gradients. Experiments that explored the effects of ionic substitution/ion channel blockers upon membrane current/potential showed that resting Vm was dependent upon a hyperpolarizing K(+) current that flowed via channels that displayed only weak voltage dependence and limited (∼7-fold) K(+) versus Na(+) selectivity. This conductance was blocked by quinidine (0.3 mM), bupivacaine (3 mM) and clofilium (50 µM), NNC55-0396 (2 µM) and mibefradil (30 µM), but not by 4-aminopyridine (2 mM, 4-AP). Progesterone had no effect upon the hyperpolarizing K(+) current. Repolarization after a test depolarization consistently evoked a transient inward 'tail current' (ITail) that flowed via a second population of ion channels with poor (∼3-fold) K(+) versus Na(+) selectivity. The activity of these channels was increased by quinidine, 4-AP and progesterone. Vm in human sperm is therefore dependent upon a hyperpolarizing K(+) current that flows via channels that most closely resemble those encoded by Slo3. Although 0.5 µM progesterone had no effect upon these channels, this hormone did activate the pharmacologically distinct channels that mediate ITail. In conclusion, this study reveals three functionally and pharmacologically distinct cation channels: Ik, ITail, ICatSper.
Medical Research Institute, College of Medicine, Dentistry and Nursing, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9S, UK.
S A
SA
Mansell
S J
SJ
Publicover
C L R
CL
Barratt
S M
SM
Wilson
D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D005306:Fertilization / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism*
C438823:CATSPER1 protein, human; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D011374:Progesterone; D012964:Sodium; D011188:Potassium; D002118:Calcium
CatSper; K+ channel; fertilization; patch clamp recording; spermatozoa