Control of Ion Transport in Mouse Proximal and Distal Colon by Prolactin

Abstract

The lactogenic hormone prolactin (PRL) has been known to affect Ca²⁺ and electrolyte transport in the intestinal epithelium. In the present study we analyzed ion transport in mouse proximal and distal colon, and acute changes induced by PRL. In the proximal colon, carbachol activated a Ca²⁺ dependent Cl^- secretion that was sensitive to DIDS and NFA. In the distal colon, both ATP and carbachol activated K⁺ secretion. Ca²⁺ -activated KCl transport in proximal and distal colon was inhibited by PRL (200ng/ml), while amiloride sensitive Na⁺ absorption and cAMP induced Cl^- secretion remained unaffected. Luminal large conductance Ca²⁺ -activated K⁺ (BK) channels were largely responsible for Ca²⁺ -activated K⁺ secretion in the distal colon, and basolateral BK channels supported Ca²⁺ -activated Cl^- secretion in the proximal colon. Ca²⁺ chelating by BAPTA-AM attenuated effects of carbachol and abolished effects of PRL. Both inhibition of PI3 kinase with wortmannin and blockage of MAP kinases with SB 203580 or U 0126, interfered with the acute inhibitory effect of PRL on ion transport, while blocking of Jak/Stat kinases with AG 490 was without effects. PRL attenuated the increase in intracellular Ca²⁺ that was caused by stimulation of isolated colonic crypts with carbachol. Thus PRL inhibits Ca²⁺ dependent Cl^- and K⁺ secretion by interfering with intracellular Ca²⁺ signaling and probably by activating PI3 kinase and MAP kinase pathways.

Upregulation of colonic ion channels in APC Min/+ mice

“…Moreover, cAMP-and Ca 2+ -activated currents were similar in wt and APC Min/+ , and the effects of paxillin, astemizole, or 4-AP could not be detected (data not shown). Thus, Ca 2+ -activated BK channels and astemizole-sensitive Eag-1 channels are most likely expressed in the surface epithelium, which confirms previous results [24]. RPD due to activation of BK K + channels.…”

“…However, Akt may also increase the activity of Ca 2+ -activated K + cannels, since membrane trafficking of BK channels was shown to be enhanced by Akt in a PI3-kinase-dependent manner in neurons [6]. PI3-kinase-dependent regulation of BK was also found in mouse distal colon [24]. BK β1 and BK β2 subunits were largely increased in the distal colon of APC Min/+ animals (Fig.…”

Anoctamins support calcium-dependent chloride secretion by facilitating calcium signaling in adult mouse intestine

“…However, previous work suggested that also Ano10 is able to produce Ca 2+ -activated Cl − currents [43,49,51]. The present data indicate expression of a number of anoctamin paralogues in mouse intestine, with Ano1 and Role of Ano1 for intestinal Cl − secretion Ca 2+ -dependent Cl − secretion was detected in rat and mouse naïve colonic epithelium, in contrast to the human large intestine, which does not express anoctamin 1 [18,24,29,40]. It is noteworthy that analysis of anoctamin expression and Ca 2+ -dependent transport should take place in naïve intestinal mucosa rather than in cultured epithelial cells, since cultured cells behave differently, even when grown under polarized conditions [24].…”

Eag1 and Bestrophin 1 Are Up-regulated in Fast-growing Colonic Cancer Cells

“…When stimulated by secretagogues such as ATP and carbachol that increase the intracellular Ca 2ϩ concentration, predominantly K ϩ channels are activated, hyperpolarizing the membrane voltage. This is comparable with colonic crypt cells, which also activate Ca 2ϩ -activated K ϩ channels upon stimulation of basolateral muscarinic M3 and apical purinergic P2Y 2 receptors (18,19). In contrast, T 84 cells that had undergone spontaneous transformation were remarkably different: they proliferated much faster, were unable to polarize or form tight monolayers when grown on permeable supports, showed typical features of malignancy, and had different membrane conductances.…”