Molecular Cell Physiological Study on Paneth Cell Function

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It is widely accepted that the small internal crypt is a ClィイD1-ィエD1 secreting epithelium where CFTR CIィイD1-ィエD1 channels are thought to mediate cyclic AMP-dependent CIィイD1-ィエD1 exit at the luminal membrane. Actually, abundant expression of CFTR mRNA in the small intestine has been shown by in situ hybridization. Paneth cells, which locate at the crypt base, have been implicated as components of the mucosal immunity and host defense by secreting anti-microbial substances, such as crypidins and lysozymes. Recently, the channel-forming crypidins have been reported to serve an apically localized C1ィイD1-ィエD1 conductance, thereby contributing to the intestinal CIィイD1-ィエD1 secretion. However, there has been no investigation as to whether Paneth cells express CFTR C1ィイD1-ィエD1 channels. In the present study, whole-cell patch clamp was first applied to Paneth cells in crypts isolated from guinea pig small intestine. Prominent activation of ClィイD1-ィエD1 currents could be observed only after stimulation with VIP or dibutyryl cyclic AMP plus forskolin. The current characters, including the current-voltage relationship, anion selectivity and DIDS-insensitivity, were phenotypically similar to those of CFTR CIィイD1-ィエD1 channel. However, both single-cell RT-PCR analysis and immunocytochemical staining failed to provide relevant evidence for molecular expression of the CFTR mRNA and protein. Thus, it is concluded that Paneth cells express cyclic AMP-activated CI' channels, but CFTR would not be the molecular identity of the ClィイD1-ィエD1 channel in Paneth cells of the guinea pig small intestine.