Endocrine Abstracts

Inguinal subcutaneous fat, the site of murine mammary glands 4 and 5, is a suitable model of mammary white fat adipose tissue (WAT). WAT requires extracellular Ca²⁺ influx for differentiation and expansion; this primarily occurs via plasma membrane Ca²⁺ voltage-dependent channels (CaVs). Whereas the neuropeptide oxytocin can mobilise intracellular Ca²⁺ in WAT which has key roles in lactation. Our aim was to use a combination of molecular biology and calcium imaging to determine if post-pubescent differences exist in CaV expression and oxytocin Ca²⁺ responses between the sexes. We used qPCR on inguinal subcutaneous fat depots from pre (P14-30) and post-pubescent (>P140) male and female rats to explore their CaV expression profile. We measured cytosolic Ca²⁺ concentration, [Ca²⁺]_i, in adipocytes isolated from inguinal fat pads of post-pubescent CD-1 mice (P32-84) with epifluorescent videomicroscopy. CaV expression was dependent on age and sex. A rank order of CaV1.2> CaV1.3>CaV3.1>CaV3.2 >Cav3.1 was observed in adult males but not females where the rank order was CaV3.1 = CaV1.2> CaV1.3>CaV3.1>CaV3.2. CaV3.1 expression was significantly larger in females compared to males; a difference not seen in pre-pubescent animals. No difference was seen in either diameter or basal [Ca²⁺]_i between adult male and female mouse inguinal adipocytes. However, we observed an association between sex and the adipocyte’s ability to respond to oxytocin: 52% of males compared to 100 % of females. The type of Ca²⁺ response was also associated with sex where only 14% of male responders demonstrated oscillations compared to 32% of female cells. We show that changes in Ca²⁺ voltage-dependent channel expression patterns and Ca²⁺ mobilization occur during adipogenesis in inguinal subcutaneous fat. Consequently, CaV3.1 and oxytocin are potential pharmacological targets to modulate adipogenesis and lactation in the development and function of mammary glands respectively.