ISSN:
1432-2013
Keywords:
Key words Colon
;
Fura-2
;
Rat colonic crypt
;
ATP
;
P2Y-receptor
;
Purinoceptor
;
Exocrine secretion
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Under resting conditions the mammalian distal colon is a NaCl-absorptive epithelium. NaCl absorption occurs at surface cells in colonic crypts. Intracellular Ca2+ or cAMP are important second messengers that activate NaCl secretion, a function that is most pronounced in crypt bases. In the present study we examined the effect of extracellular ATP on isolated crypts of rat distal colon using the fura-2 technique. Intracellular Ca2+ ([Ca2+]i) was measured spectrofluorimetrically either by photon counting or video imaging. ATP reversibly increased [Ca2+]i in crypt base cells with an EC50 of 4.5 μmol/l (n = 11). This [Ca2+]i increase was composed of an initial peak, reflecting intracellular store release, and a secondary plateau phase reflecting transmembrane influx. Digital video imaging revealed that agonist-induced [Ca2+]i elevations were most marked at the crypt base. In the middle part of the crypt ATP induced smaller increases of [Ca2+]i (peak and plateau) as compared to basal cells and in surface cells this [Ca2+]i transient was even further reduced. Attempts to identify the relevant P2-receptor demonstrated the following rank order of potency: 2MeS-ATP 〉 ADP ≥ ATP 〉〉 AMP 〉 UTP 〉 AMP-PCP 〉 adenosine. In Ussing chamber experiments ATP (1 mmol/l) functioned as a secretagogue, increasing transepithelial voltage (V te) and equivalent short-circuit current (I sc): ΔI sc = –36.4 ± 5.4 μA/cm2, n = 17. Adenosine itself (1 mmol/l) induced an increase of I sc of similar magnitude to that induced by ATP: ΔI sc = –55.1 ± 8.4 μA/cm2, n = 9. The effect of adenosine, but not that of ATP, was fully inhibited by the A1/A2-receptor antagonist 8-(p-sulphophenyl)theophylline, 0.5 mmol/l, n = 4. Together these data indicate that: (1) basolateral ATP induces [Ca2+]i in isolated rat colonic crypts and acts as a secretagogue in the distal rat colon; (2) a basolateral P2Y-receptor is responsible for this ATP-induced NaCl secretion; (3) the ability of ATP to increase I sc in Ussing chamber experiments is not mediated via adenosine; and (4) the agonist-induced [Ca2+]i signals are mostly located in the crypt base, which is the secretory part of the colonic crypt.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/PL00008079
