Effect of urinary trypsin inhibitor on potassium currents: fetus modulates membrane excitability by production of UTI.
BACKGROUND
Amniotic fluid contains a significant level of urinary trypsin inhibitor (UTI). Previously, we reported that UTI inhibits calcium influx of myometrium and it is effective in preventing uterine contraction. This study examined the effects of UTI upon potassium channels, which is important for membrane excitability.


METHODS
Whole-cell patch-clamp recordings were performed in fibroblasts derived from human fetal skin. Potassium currents were recorded and the effects of exogenous UTI and/or cadmium determined.


RESULTS
Tetraethylammonium sensitive potassium currents were elicited by step or ramp stimulations at depolarized membrane potentials (over +30 mV). Administration of 1 micro M UTI significantly increased these potassium currents by 16.9%. When calcium channels were blocked by the administration of cadmium, UTI increased the rest of the potassium currents by 4.8%. This indicates that UTI increased calcium-dependent potassium currents by 94.8% but only increased voltage-dependent potassium currents by 4.8%.


CONCLUSIONS
Urinary trypsin inhibitor is a physiological substance of fetal origin that modulates calcium-dependent and voltage-dependent potassium channels. These data suggest that UTI is capable of regulating the membrane properties of the fetal and myometrial cells in contact with amniotic fluid.
Takeuchi
Kinya
K
Department of Obstetrics and Gynecology, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu, Shizuoka 431-3192, Japan. takeuchi@hama-med.ac.jp
Fukuda
Atsuo
A
Kanayama
Naohiro
N
D000653:Amniotic Fluid; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D005260:Female; D005333:Fetus / Q000473:pathology / Q000502:physiology; D005347:Fibroblasts / Q000187:drug effects*; D006023:Glycoproteins / Q000494:pharmacology*; D006801:Humans; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D011247:Pregnancy; D012867:Skin / Q000166:cytology
D006023:Glycoproteins; D015221:Potassium Channels; D002104:Cadmium; C028665:urinastatin; D002118:Calcium