Ca 2+ regulation in detrusor smooth muscle from developing fetal sheep bladders

Abstract

Sheep fetus is a useful model to study in utero bladder outflow obstruction but little is known about cell physiology of fetal bladders. To remedy this defect we have characterised intracellular Ca 2+ regulation in fetal sheep myocytes of different developmental ages. Fetal detrusor myocytes had a similar resting [Ca 2+] i to adult cells and exhibited transient [Ca 2+] i increases in response to carbachol, ATP, high-K, caffeine and low-Na. The carbachol transients were abolished by atropine and caffeine; the ATP response was blocked by α,β-methylene ATP; high-K-evoked [Ca 2+] i rises were antagonised by verapamil. The maximal responses to carbachol, high-K, caffeine and low-Na in fetal cells were similar to those of adult counterparts, whilst the ATP response was smaller ( p < 0.05). These variables were largely similar between the three gestational groups with the exception of ATP-induced response between early fetal and adult bladders ( p < 0.05). Dose–response curves to carbachol demonstrated an increase of potency between mid-gestation and early adulthood ( p < 0.05). These data show that muscarinic receptors coupled to intracellular Ca 2+ release, P2X receptor-linked Ca 2+ entry, depolarisation-induced Ca 2+ rise via L-type Ca 2+ channels, Na +/Ca 2+ exchange and functional intracellular Ca 2+ stores are all operational in fetal bladder myocytes. Whilst most of Ca 2+ regulators are substantially developed and occur at an early fetal age, a further functional maturation for cholinergic sensitivity and purinergic efficacy continues throughout to adulthood.