Milk secretion involves significant flux of water, driven largely by synthesis of lactose within the Golgi apparatus. It has not been determined whether this flux is simply a passive consequence of the osmotic potential between cytosol and Golgi, or whether it involves regulated flow. Aquaporins (AQPs) are membrane water channels that regulate water flux. AQP1, AQP3 and AQP5 have previously been detected in mammary tissue, but evidence of developmental regulation (altered expression according to the developmental and physiological state of the mammary gland) is lacking and their cellular/subcellular location is not well understood. In this paper we present evidence of developmental regulation of all three of these AQPs. Further, there was evidence of reciprocity since expression of the rather abundant AQP3 and less abundant AQP1 increased significantly from pregnancy into lactation, whereas expression of the least abundant AQP5 decreased. It would be tempting to suggest that AQP3 and AQP1 are involved in the secretion of water into milk. Paradoxically, however, it was AQP5 that demonstrated most evidence of expression located at the apical (secretory) membrane. The possibility is discussed that AQP5 is synthesized during pregnancy as a stable protein that functions to regulate water secretion during lactation. AQP3 was identified primarily at the basal and lateral membranes of the secretory cells, suggesting a possible involvement in regulated uptake of water and glycerol. AQP1 was identified primarily at the capillary and secretory cell cytoplasmic level and may again be more concerned with uptake and hence milk synthesis, rather than secretion. The fact that expression was developmentally regulated supports, but does not prove, a regulatory involvement of AQPs in water flux through the milk secretory cell.

minimum force between oscillations by 30 ± 5% ( n = 9) in pig detrusor strips ( P < 0.005). In the presence of 10 μ M NS4591, carbachol (1 μ M) induced rhythmic contractions with an amplitude and normalized mean power frequency (nmeanPF) of 8.4 ± 5.1% and 0.11 ± 0.06 mN root mean square (rms) Hz ( n = 12), respectively, vs. 21 ± 3.4% and 0.17 ± 0.04 mN rms Hz in control strips ( n = 13). Apamin induced 6-and 11-fold increases in amplitude and nmeanPF vs. 1.3-and 2-fold increases in control strips.• In human detrusor strips ( n = 15), the cumulative addition of NS4591 (1-30 μ M) significantly reduced the amplitude by 69 ± 11%, the nmeanPF by 78 ± 6% and the minimum force between carbachol-induced oscillations by 59 ± 5% ( P < 0.008). The addition of apamin (0.3 μ M) before application of 1 μ M carbachol abolished the effects of NS4591 on amplitude and partially abolished its effect on nmeanPF by 41 ± 7%, vs. a 78 ± 6% reduction in the absence of apamin ( n = 8).• In spontaneously active detrusor preparations, NS4591 reduced or abolished contractions.• Furthermore, NS4591 (10 μ M) decreased the carbachol-induced increase in the fura-2 ratio by 43 ± 3% compared with control ( n = 12) ( P < 0.03). CONCLUSIONS• The SK/IK channel modulator NS4591 inhibits EFS-and carbachol-induced contractions in rat, pig and human detrusor muscle.• NS4591 may have therapeutic potential for treatment of detrusor overactivity. KEYWORDS detrusor, SK channels, NS4591, OABWhat's known on the subject? and What does the study add? Increased urinary bladder detrusor smooth muscle phasic contractility has been suggested to be associated with idiopathic bladder overactivity. Small conductance Ca2 + -activated K + (SK 1-3) channels have attracted considerable interest as putative target for new therapeutic strategy for treating overactive bladder. These channels play an important role in regulating the function and activity of urinary bladder smooth muscle (UBSM), and the loss of SK channel function has been shown to increase UBSM excitability and contractility. However, it is not known whether activation of SK channels has the converse effect of reducing UBSM excitability and contractility. In this paper, we investigated this possibility in the rat, pig and human UBSM by using the novel SK channel opener NS4591. These studies demonstrate that the SK channel modulator NS4591 has a potential role as a pharmacological tool to study the involvement of SK (and IK) channels in mammals and rodents urinary bladder. NS4591 may have therapeutic potential for treatment of detrusor overactivity. OBJECTIVE • To investigate the importance of small (SK)-and intermediate (IK)-conductance Ca2+ -activated K + channels on bladder function, by studying the effects of 4,5-dichloro-1,3-diethyl-1,3-dihydrobenzoimidazol-2-one (NS4591), a new modulator of SK/IK channels, on contractions induced by electrical field stimulation (EFS) and carbachol in rat, pig and human detrusor. PATIENTS AND METHODS• Detrusor biopsies were obtained from rats, pigs and male patients unde...

Preterm births accounts for roughly 9% of all births worldwide and can have detrimental or even lethal consequences for the infant. However to develop new treatment that will lower the rate of preterm births, more knowledge is required on the factors contributing to the contraction and relaxation of the myometrium. The small conductance Ca2+-activated potassium channel subtype 3 (SK3) has been identified in the myometrium of several species including humans, mice and rats, but with great inter species variation of the expression pattern and regulation. The aim of this study was to investigate the expression of SK3 in the uterus of rats stimulated with 17β-estradiol and progesterone in order to get an in depth understanding of the rat uterine SK3. Using immunohistochemistry SK3 was localized to the glandular and luminal endometrial lamina epitheliali. Furthermore, a weak signal was observed in the myometrium. Using Western blot the protein level of SK3 was found to increase in uteri from animals treated with 17β-estradiol, an effect that was not reflected at the mRNA level. The levels of mRNA for SK3 were significantly lower in the uterus of 17β-estradiol-treated animals than in the uterus of ovariectomized animals. We conclude that the SK channels are present in the endometrial epithelium, and possibly also in the myometrium of the rat uterus. Furthermore, the hormonal effect on SK3 caused by 17β-estradiol includes divergent regulation at mRNA and protein levels.

The human myometrium is mainly relaxed during pregnancy, but, up to term, contractions become more coordinated and forceful in order to initiate delivery. Small conductance Ca2+-activated K+channels (SK channels) in human myometrium have been shown to be downregulated in late pregnancy. The aim was to investigate the presence of SK2 and SK3 in the human myometrium from nonpregnant women, pregnant women at term, and pregnancies delivered preterm and, in addition, to characterize the time of downregulation of these channels. Using qRT-PCR, we observed significantly lower levels of mRNA for SK2 than for SK3 in the nonpregnant tissue. The mRNA levels of SK3 were significantly reduced in tissue from pregnancies at term and pregnancies resulting in preterm deliveries, whereas no downregulation for SK2 was observed. Western blotting confirmed the qRT-PCR results. Using immunohistochemical staining, both SK2 and SK3 were detected in endometrial glandular epithelium. We conclude that SK3 mRNA is downregulated early in pregnancy—at least among those that result in preterm deliveries. Furthermore, we find that SK channels are expressed not only in the uterine smooth muscle but also in the endometrial epithelium.