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¹ Department of Physiology I
² Geriatric and Respiratory Medicine, Tohoku University Graduate School of Medicine, Sendai 980-8575, Japan

Epithelial secretory cells display cell-specific mechanisms of fluid secretion and express large conductance voltage- and Ca²⁺-activated K⁺ (Maxi-K) channels that generate the membrane negativity for effective Cl^– exit to the lumen. Rat and mouse pancreatic acinar cells had been thought to be peculiar in this sense because of the previously reported lack of Maxi-K channels. However, this view is not entirely correct as evidenced in the present paper. Searching for their presence in pancreatic acinar cells in mice from 5 to 84 weeks of age with patch-clamp current measurements, we demonstrated that the expression of Maxi-K channels is regulated in an age-associated manner after birth. The expression started at approximately 12 postnatal weeks and increased steadily up to 84 weeks. In support of this, RT-PCR could not detect mSlo mRNA, the Maxi-K gene, at either 7 or 8 weeks but could at 58 and 64 postnatal weeks. These results suggest that a key steering element for fluid secretion, the Maxi-K channel, is progressively re-organized in rodent pancreas. A pancreatic secretagogue, acetylcholine, evoked Maxi-K channel current overlapping to various degrees on the previously known current response. This suggests that the rise in internal Ca²⁺ activates Maxi-K channels which reshape the mode of secretagogue-evoked current response and contribute to Cl^– driving in fluid secretion in an age-associated fashion.

(Received 20 October 2004; accepted after revision 16 December 2004; first published online 20 December 2004)
Corresponding author Y. Maruyama: Department of Physiology 1, Tohoku University Graduate School of Medicine, 2–1, Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan. Email: ymaruyama{at}cellphysiol.med.tohoku.ac.jp

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