Gestational change in Na+ and Ca2+ channel current densities in rat myometrial smooth muscle cells.
The change of Na+ and Ca2+ channel currents during gestation was investigated using the whole cell voltage-clamp method on single smooth muscle cells freshly isolated from the longitudinal layer of pregnant rat uterus. The current-voltage relationships for both the Na+ and Ca2+ currents did not change during gestation. The threshold voltage, the voltage at the peak inward current, and the reversal potential (extrapolated) were virtually identical. The averaged current densities of Ca2+ channel were almost unchanged between days 9 and 21; this value at day 5 was somewhat lower. In contrast, the averaged current density of fast Na+ channels increased markedly in the myometrium during gestation: from 0 at day 5 to 0.19 +/- 0.16 at day 9, to 0.56 +/- 0.13 at day 14, to 0.90 +/- 0.13 at day 18, and to 0.86 +/- 0.14 pA/pF at day 21. This almost linear increase in the averaged density of fast Na+ channels during gestation occurs because of an increase in the fraction of cells which possessed fast Na+ channels. These results suggest that the role of fast Na+ channels in myometrial activity becomes more and more important as term approaches. We suggest that the fast Na+ current may be involved in spread of excitation.
Inoue
Y
Y
Department of Physiology and Biophysics, University of Cincinnati College of Medicine, Ohio 45267-0576.
Sperelakis
N
N
D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D005260:Female; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000502:physiology*; D009215:Myometrium / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D051381:Rats; D015222:Sodium Channels / Q000502:physiology*
D015220:Calcium Channels; D015222:Sodium Channels