Voltage-gated calcium channels play a key role in mediating excitation-contraction coupling in the uterus, as they both enable calcium to enter the cell and also play a role in determining the action potential duration. The expression levels of mRNA for many ion channels has been shown to be regulated in part by hormones, so we determined the relative expression levels of voltage-gated calcium channels in the mouse uterus at vaious stages of the estrous cycle. The stage of the estrous cycle was determined by taking vaginal smears continuously for 3 weeks from female C57/BL mice. Four to Five mice were in each of the phases of estrous, namely estrus, protestrus, and diestrus. The mice were sacrificed at the end of the three week period, and the uterus removed. quantitative real-time PCR was performed to determine relative expression of voltage gated calcium channels. All primers were purchased from SABIOSCIENCES, and qRT-PCR was performed using a BioRad ICycler. We determined mRNA expression in the uterus for six distinct voltage gated calcium channels: Cacna1a (P/Q type, alpha 1A subunit, Cav2.1), Cacna1b (N type, alpha 1B subunit, Cav2.2), Cacna1c (L type, alpha 1C subunit, Cav1.2), Cacna1g (T type, alpha 1G subunit, Cav3.1d), Cacna1h (T type, alpha 1H subunit, Cav3.2), Cacna1s (L type, alpha 1S subunit, Cav1.1). mRNA Expression was normalized to 5 housekeeping genes (beta Glucuronidase, beta, Hypoxanthine guanine phosphoribosyl transferase 1, Heat shock protein 90 alpha (cytosolic), class B member 1, Glyceraldehyde-3-phosphate dehydrogenase, and beta actin). For all preparations, Cacna1s was not present, or had a cycle threshold above 37. For channel Cacna1b, the lowest threshold was 34 cycles, i.e., there was very low expression, if any. For the remaining four channels, we determined the changes in global and relative expression of these channels in the mouse uterus during the estrous cycle. For all 4 channels, we ranked the relative order of expression. The most abundant mRNA was that for the Cacna1h subunit (T type). The least abundant mRNA was Cacna1a (P/Q type). Overall, the order of expression was Cacna1h > Cacna1g > Cacna1c > Cacna1a. Changes in expression during the estrous cycle did not affect the relative order of expression. Expression of Cacna1h and Cacna1c were not dependent on estrus cycle phase. However, the expression of Cacna1a and Cacna1g mRNAs, were significantly different during the estrous cycle, as Cacna1a and Cacna1g channel mRNA expression was reduced during proestrus compared to the estrus phase (n=5, p<0.05, students t-test). These results are consistent with the previous reports of relative reduction in electrical activity in proestrus in the myometrium (see Wray and Noble, 2008).