Dietary taurine is essential for cats, and deficiency during pregnancy may lead to abortion, growth retardation or impaired neurological function of kittens. A cat placental fragment model has identified Na+ and Cl–-dependent taurine transport by system β (Champion et al. 2001). Here we describe long-term culture of cat placental explants as a model to study chronic regulation of amino acid transport in this species. Explant viability was assessed by examining explant morphology, endocrine function and by characterising taurine uptake on day 7.
Cat placentas were collected after natural, normal litter production, with full consideration of cat welfare. Explants (~10 mg wet weight) were cultured in supplemented CMRL-1066 medium for 11 days. Medium was assayed for PGF2α as a measure of endocrine function and lactate dehydrogenase (LDH) as a measure of cellular integrity. On days 2, 5, 7 and 11 explants were fixed in 2.5 % (v/v) glutaraldehyde and embedded in epoxy resin. Semi-thin sections (0.5 µm) were stained with 1 % toluidine blue in 1 % borax. On day 7 [3H]taurine uptake was measured ± Na+ using methods described previously (Champion et al. 2001). Na+-dependent taurine uptake, attributable to system β, was calculated as the difference between uptake in the presence and absence of Na+ (Fig. 1).
PGF2α release in pmol (mg protein)-1 h-1 was 158.7 ± 46.6 at day 2 and increased to stabilise at a mean of 303.2 ± 15.1 over days 3-11 (n = 5; means ± S.E.M.). LDH activity decreased from 264.7 to 61.9 U l-1 (mg protein)-1 at days 2 and 11, respectively (n = 1). Morphological examination on days 2 and 5 revealed explants of typical lamellar structure. As time progressed, new growth in the lamellar region formed atypical structures whilst degeneration and disruption of the original lamellae architecture occurred.
Taurine uptake into explants at day 7 exhibited characteristics typical of system β. Endocrine function was preserved to day 11 and explant structure to day 5. This in vitro culture system may be useful for the study of chronic regulation of amino acid transport by the cat placenta.