Gestational change in Na+ and Ca2+ channel current densities in rat myometrial smooth muscle cells

Am J Physiol. 1991 Mar;260(3 Pt 1):C658-63. doi: 10.1152/ajpcell.1991.260.3.C658.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium Channels / physiology*
  • Female
  • In Vitro Techniques
  • Membrane Potentials
  • Muscle, Smooth / physiology*
  • Myometrium / physiology*
  • Pregnancy
  • Pregnancy, Animal / physiology*
  • Rats
  • Sodium Channels / physiology*


  • Calcium Channels
  • Sodium Channels