Regulation of the Ca2+-sensitive domains of the maxi-K channel in the mouse myometrium during gestation.
Large conductance Ca(2+)-activated K(+) channels (maxi-K channels) are known to modulate uterine activity during gestation. Electrophysiological recordings demonstrate that myometrial maxi-K current is suppressed in term-pregnant compared to non-pregnant mice. We sought to determine whether maxi-K current suppression is due to reduction of maxi-K channel protein or differential expression of maxi-K channel isoforms that vary in their Ca(2+) and voltage sensitivities. Immunoblot analyses show an increase of maxi-K channel protein throughout gestation. Polymerase chain reaction of mouse myometrial cDNA identified four alternatively spliced sites within the maxi-K transcript and three within the Ca(2+)-sensitive "tail" domain. Ribonuclease protection analyses demonstrate that total channel transcript levels mimic protein expression; however transcript levels of alternatively spliced regions of regulatory domains that alter sensitivity to voltage and Ca(2+) differ in their gestational expression. An insert that increases the maxi-K channel sensitivity to voltage and Ca(2+) is present at steady levels throughout gestation, differing from total channel transcript regulation. The insert-less form of this transcript, which reduces the channel voltage and Ca(2+) sensitivity, is not detected until midterm pregnancy. These findings verify that multiple isoforms of the maxi-K channel are present in the mouse myometrium and are regulated differentially during gestation, which is a likely mechanism for modulation of myometrial excitability during pregnancy.
Benkusky
N A
NA
Department of Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242, USA.
Fergus
D J
DJ
Zucchero
T M
TM
England
S K
SK
D017398:Alternative Splicing; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D005786:Gene Expression Regulation; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D008958:Models, Molecular; D009215:Myometrium / Q000502:physiology*; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D017433:Protein Structure, Secondary; D014158:Transcription, Genetic
D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D002118:Calcium