Voltage-gated potassium channels (K_v) are involved in the control of myogenic tone of resistance uterine arteries therefore they could determine the blood flow to the placenta and fetus.

Aims: 

We explored biophysical characteristics of transmembrane outward ion currents in smooth muscle cells (SMCs) of uterine arteries from late pregnant rats (LP) compared to those form nonpregnant (NP) controls.

Methods: 

SMCs from radial uterine arteries of NP or LP were isolated using papain and 1,4-dithioerythritol. Currents were recorded using conventional whole-cell voltage-clamp technique by Axopatch 200B amplifier, Digidata 1322A and pCLAMP-9 software (Axon Instruments, CA).

Results: 

SMCs from LP had a significantly larger cell capacitance compared to SMCs from NP. Outward current density was reduced in LP myocytes compared to NP. 4-AP (5mM) dramatically decreased current amplitude. The density of the 4-AP-sensitive K_v currents was significantly reduced in SMCs from LP animals relative to NP controls. Steady-state activation and inactivation studies displayed that the entire window of the current in SMCs of LP moved to rather negative voltages, was relatively wider, with steeper kinetics than in SMCs of NP.

Conclusion: 

These data demonstrate that the density of outward currents through 4-AP-sensitive K _v channels was significantly diminished in SMCs of LP vessels compared to those of NP. It correlates with the increased capacitance of SMCs, which most likely reflects a significant enlargement of SMCs during gestation. Our data suggest that pregnancy may down-regulate function of K_v channels in rat uterine arteries. Supported by NIH R01 HL-067250.