Functional Morphology of the Large Intestine

Lacy, Eric R.

doi:10.1002/cphy.cp060404

Cited by 9 publications

(12 citation statements)

References 388 publications

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“…Thus guinea-pig distal colon has larger K+ secretory currents than rabbit or rat colon because of a higher intrinsic apical H+-K+ pumping capacity. Mammalian colonic epithelia consist of a surface cell layer invaginated by numerous crypts of Lieberkiihn (Lacy, 1991). Changes in cell Na+ and Cl-concentration associated with adrenaline stimulation indicate that crypt columnar cells are the likely K+ secretory cell type (Halm & Rick, 1992;Halm et al 1993).…”

Section: Interrelations Among Ion Transport Pathwaysmentioning

confidence: 99%

See 1 more Smart Citation

Active potassium transport across guinea‐pig distal colon: action of secretagogues.

Rechkemmer¹,

Frizzell²,

Halm³

1996

The Journal of Physiology

123

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1. Adrenaline (5 uM) stimulated a K+ secretory current by 2-2 ftequiv h-' cm2 in isolated guinea-pig distal colonic epithelium. This secretory activity was inhibited entirely by addition of the loop diuretic bumetanide to the serosal solution. On-going K+ uptake via the absorptive pathway was unaltered by these changes.2. Prostaglandin E2 (PGE2, 2 /M) stimulated electrogenic K+ secretion and Cl-secretion by 3 0 and 3-6 ,tequiv h-cmM2, respectively. Serosal addition of bumetanide completely inhibited this K+ secretion but blocked only -70% of Cl-secretion. The bumetanideinsensitive Cl-secretory current was dependent on the presence of Cl-and HC03-in the bathing solutions. 3. Stimulation of electrogenic K+ secretion by PGE2 occurred with a half-maximal concentration of 4 nm, an affinity -300 times higher than that for stimulation of Clsecretion by PGE2.4. Forskolin (10 AM) stimulated Cl-secretion by 4-9 tequiv h-' cm2. The apparent K+ secretory rate was increased by only 1-5 ytequiv h-1 cm2. A bumetanide-insensitive shortcircuit current (Isc) was apparent and of the same size as that stimulated by PGE2.5. Addition of the Ca2+ ionophore A23187 (10 fSM), in the presence of indomethacin (1 /SM) to reduce prostaglandin production, inhibited the K+ absorptive pathway by 40% and concurrently stimulated a small rate of electrogenic K+ secretion. 6. Active K+ absorption was inhibited by the addition of ouabain, omeprazole or SCH28080 to the mucosal solution. Both omeprazole and SCH28080 also stimulated a small negative Isc, consistent with electrogenic K+ secretion. 7. Association of K+ absorption, K+ secretion and Cl-secretion is indicated by similarities in transport mechanism and by secretagogue regulation. In particular, maximal rates of K+ secretory current require uptake via apical membrane K+ pumps. Such interrelations support a common cellular locus for these ion transport pathways.Potassium transport across the epithelium lining mammalian distal colon occurs via both active secretory and active absorptive pathways (Halm & Frizzell, 1991). Regulation of these two oppositely directed transport processes permits a range of net flows. Active flow of K+ through the secretory pathway proceeds via a cellular mechanism similar to that for Cl-secretion ; uptake of K+ occurs through Na+-K+ pumps and Na+-K+-2Cl-cotransporters in the basolateral membrane with K+ exit from the cell through channels in the apical and basolateral membranes. The ratio of these K+ conductances together with K+ electrochemical gradients determine the rate of K+ secretion. A cellular mechanism for active K+ absorption has not been resolved as clearly.

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Section: Interrelations Among Ion Transport Pathwaysmentioning

confidence: 99%

“…Several transport processes serving adrenaline-stimulated K+ secretion in mammalian distal colon are also required in electrogenic Cl-secretion , 1991.…”

Section: Cellular Model For K+ Transport K+ Secretory Pathwaymentioning

confidence: 99%

Active potassium transport across guinea‐pig distal colon: action of secretagogues.

Rechkemmer¹,

Frizzell²,

Halm³

1996

The Journal of Physiology

123

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“…These observations are associated with a change in cell shape from columnar to cuboidal. An alteration of cell shape has also been observed after exposure of rabbit colon in vitro to acidic medium that led rapidly to increased cell size and to recovery of epithelial integrity (33). Thus the marked reduction of cAMP production in isolated crypts after irradiation is not associated with a significant decrease of crypt cell number.…”

Section: Discussionmentioning

confidence: 61%

Alterations of the VIP-stimulated cAMP pathway in rat distal colon after abdominal irradiation

Morel

Dublineau

Lebrun

et al. 2002

American Journal of Physiology-Gastrointestinal and Liver Physi

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Morel, E., I. Dublineau, F. Lebrun, and N. M. Griffiths. Alterations of the VIP-stimulated cAMP pathway in rat distal colon after abdominal irradiation. Am J Physiol Gastrointest Liver Physiol 282: G835-G843, 2002. First published January 9, 2002 10.1152/ajpgi.00457.2001.-Ionizing radiation induces hyporesponsiveness of rat colonic mucosa to vasoactive intestinal peptide (VIP). Possible mechanisms responsible for this hyporesponsiveness of the cAMP communication pathway in rat colon were investigated. VIP-and forskolin-stimulated short-circuit current (I sc) responses were studied after a 10-Gy abdominal irradiation in Ussing chambers as well as in single, isolated crypts. Adenylyl cyclase (AC) activity and VIP receptor characteristics were determined in mucosal membrane preparations. In addition, alterations in crypt morphology were studied. Impaired secretory responses to VIP and forskolin were observed 4 days after irradiation (decrease of 80%). cAMP analog-stimulated Isc responses were unchanged. In isolated crypts, VIP-and forskolin-stimulated cAMP accumulation was markedly reduced by 80 and 50%, respectively. VIP-stimulated AC activity and VIP receptor number were decreased in membrane preparations. No major change of cellularity was associated with these functional alterations. In conclusion, the decreased secretory responses to VIP of rat colon are associated with reduced cAMP accumulation, decreased AC activity, and diminution of VIP receptor numbers without a marked decrease of crypt cell number.

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“…Entero-endocrine and Paneth (right colon only) cells are small in number, and tend to be located in the crypt bases. In addition, undifferentiated stem cells are found in the lower 50% of the crypts [Lacy, 1991;Lewin et al, 1992]. From these observations it follows that the portion of the crypt that is studied during perfusion studies of the isolated colonic crypt consists of roughly equal numbers of goblet cells and vacuolated cells with a very small percentage of other cell types.…”

Section: Discussionmentioning

confidence: 73%

“…By inference, 49.6 and 45.3% of proximal and distal colonic crypt cells, respectively, were nongoblet cells. Nongoblet cells consist of principle cells, vacuolated cells, entero-endocrine cells, Tuft cells (caveolated cells), Paneth cells, and undifferentiated stem cells [Lacy, 1991;Specht, 1977]. Principle cells predominant on the surface and uppermost crypt, but extend into the lower crypt in the distal colon.…”

Section: Discussionmentioning

confidence: 99%

Morphology of Isolated Colonic Crypts

Robert

Singh²,

Ikuma³

et al. 2001

Cells Tissues Organs

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The traditional paradigm of colonic fluid and electrolyte transport includes a spatial separation of absorptive and secretory processes to surface and crypt cells, respectively. Recent studies of isolated microperfused colonic crypts revealed constitutive Na-dependent fluid absorption while secretion is regulated by one or more neurohumoral agonists. One obvious reason for the difference found in microdissected crypts is their separation from the lamina propria milieu. While it has been shown that isolated crypts are devoid of obvious lamina propria elements, including pericryptal fibroblasts, detailed morphologic information of the content of isolated crypts has been lacking. To characterize the morphology of the isolated crypt, we performed transmission electron microscopy (TEM) and immunofluorescence on microdissected and Ca²⁺ chelated crypts. Crypt cell type analysis was carried out separately on intact rat colon using light microscopy. TEM revealed a complete lack of either lamina propria cells or extracellular material in crypts isolated by either technique. TEM also revealed a subtle difference between the two isolation methods, with intact basal membranes in microdissected crypts but focal disruption of basal membranes in Ca²⁺- chelated crypts. Immunofluorescent stains for two basement membrane components (laminin and collagen type IV) revealed the presence of adherent basement membrane only on microdissected crypts; evidence that the plane of separation differs in these two preparations. Crypt cell type analysis on intact rat colon revealed an equal proportion of goblet cells in the right and left colon (approximately 50%) when measuring the middle 70% of the crypts – the area studied during crypt microperfusion. This morphologic analysis will increase our understanding of the observed physiology of isolated colonic crypts.

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Functional Morphology of the Large Intestine

Cited by 9 publications

References 388 publications

Active potassium transport across guinea‐pig distal colon: action of secretagogues.

Active potassium transport across guinea‐pig distal colon: action of secretagogues.

Alterations of the VIP-stimulated cAMP pathway in rat distal colon after abdominal irradiation

Morphology of Isolated Colonic Crypts

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