AIM: Functional evidence suggests the presence of two types of intracellular 
Ca(2+) channels responsible for the release of Ca(2+) from Ca(2+)-stores, i.e. 
inositol-1,4,5-trisphosphate (IP(3)R) and ryanodine receptors (RyR), in rat 
colonic epithelium. Generally, three ryanodine receptor isoforms (RyR1-RyR3) are 
known; however, the type of RyR at this epithelium is unknown and was the focus 
of the present study.
METHODS: RyRs were characterized by molecular biological and immunohistochemical 
methods in the rat colon.
RESULTS: A transcript of RyR1 was found in mRNA from colonic crypts. In 
contrast, RyR2 and RyR3 were found in their corresponding reference tissues, but 
not in the cDNA from colonic crypts suggesting a predominant expression of the 
RyR1 isoform in this epithelium. In order to characterize the subcellular 
localization of RyR1, immunohistochemical experiments were performed. They 
showed that RyR1 is present in the lamina epithelialis mucosae and smooth muscle 
cells and is distributed equally along the whole crypt axis with no difference 
between surface and crypt cells. A double staining with IP(3)R3, the dominant 
cytoplasmic isoform of IP3Rs in this epithelium, revealed that there is only 
little colocalization of the two receptor subtypes within the epithelial cells. 
Furthermore, the epithelium is equipped with the enzyme CD38 responsible for the 
production of cyclic adenosine diphosphate ribose, the physiological agonist of 
RyR. RyRs are known to be activated by changes in the redox state. The oxidant, 
monochloramine evoked a ruthenium red-sensitive Ca(2+) release all over the 
crypt axis. This release was unaffected by prior stimulation of IP(3) receptors 
with ATP (and vice versa).
CONCLUSION: The present data suggest a functional separation of IP(3)- and 
ryanodine receptor-carrying Ca(2+) stores in the colonic epithelium.