TTX-sensitive Na(+) and nifedipine-sensitive Ca(2+) channels in rat vas deferens smooth muscle cells.
The inward currents in single smooth muscle cells (SMC) isolated from epididymal part of rat vas deferens have been studied using whole-cell patch-clamp method. Depolarising steps from holding potential -90 mV evoked inward current with fast and slow components. The component with slow activation possessed voltage-dependent and pharmacological properties characteristic for Ca(2+) current carried through L-type calcium channels (I(Ca)). The fast component of inward current was activated at around -40 mV, reached its peak at 0 mV, and disappeared upon removal of Na ions from bath solution. This current was blocked in dose-dependent manner by tetrodotoxin (TTX) with an apparent dissociation constant of 6.7 nM. On the basis of voltage-dependent characteristics, TTX sensitivity of fast component of inward current and its disappearance in Na-free solution it is suggested that this current is TTX-sensitive depolarisation activated sodium current (I(Na)). Cell dialysis with a pipette solution containing no macroergic compounds resulted in significant inhibition of I(Ca) (depression of peak I(Ca) by about 81% was observed by 13 min of dialysis), while I(Na) remained unaffected during 50 min of dialysis. These data draw first evidence for the existence of TTX-sensitive Na(+) current in single SMC isolated from rat vas deferens. These Na(+) channels do not appear to be regulated by a phosphorylation process under resting conditions.
Nerve-muscle Physiology Department, Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Bogomoletz str 4, Kiev-24, Ukraine.
A E
AE
Belevych
A V
AV
Zima
I A
IA
Vladimirova
H
H
Hirata
A
A
Jurkiewicz
N H
NH
Jurkiewicz
M F
MF
Shuba
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002469:Cell Separation; D004305:Dose-Response Relationship, Drug; D008297:Male; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology*; D014649:Vas Deferens / Q000166:cytology / Q000378:metabolism*
D015220:Calcium Channels; D015222:Sodium Channels; D013779:Tetrodotoxin; D009543:Nifedipine