Gestational changes in uterine L-type calcium channel function and expression in guinea pig

Area of Science:

• Reproductive biology
• Molecular physiology
• Pharmacology

Background:

• Pregnancy significantly alters uterine myometrium function, affecting resting membrane potential and ion channel composition.
• Calcium flux, crucial for uterine excitation-contraction coupling, is mediated by L-type calcium channels.
• These channels are implicated in the physiological process of parturition.

Purpose of the Study:

• To investigate gestational changes in uterine contractile responses to L-type calcium channel agonist Bay K 8644.
• To analyze gestational variations in the mRNA expression of L-type calcium channel subunits.
• To quantify L-type calcium channel protein levels using radioligand binding assays.

Main Methods:

• Assessed uterine contractile response to Bay K 8644 at different gestational stages.
• Employed semiquantitative reverse transcriptase-polymerase chain reaction to measure mRNA expression of channel subunits.
• Utilized (3)H-isradipine saturation binding to estimate dihydropyridine binding site levels on the alpha(1c) subunit.

Main Results:

• Uterine sensitivity to Bay K 8644 increased from 0.8 gestation through term.
• This heightened sensitivity correlated with increased mRNA expression of alpha(1c) and beta(2) subunits.
• A novel alpha(1c) transcript variant with a significant protein deletion was identified; isradipine binding was lowest during this period.

Conclusions:

• Guinea pig uterine L-type calcium channel activity is tightly regulated during gestation.
• Regulation of mRNA expression and protein levels may differ, as indicated by isradipine binding.
• Upregulation of channel function, alpha(1c) mRNA, and binding at term supports its role in parturition.