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Regulation of slowly activating potassium current (I_Ks) by secretin in rat pancreatic acinar cells

Sung Joon Kim, Jin Kyoung Kim *, Hermann Pavenstädt †, Rainer Greger *, Martin J. Hug * and Markus Bleich ‡

1. The secretagogue-activated K⁺ conductance is indispensable for the electrogenic Cl^- secretion in exocrine tissue. In this study, we investigated the effect of secretin and other cAMP-mediated secretagogues on the slowly activating voltage-dependent K⁺ current (I_Ks) of rat pancreatic acinar cells (RPAs) with the whole-cell patch clamp technique.
2. Upon depolarization, RPAs showed I_Ks superimposed upon the instantaneous background outward current. Secretin (5 nM), vasoactive intestinal peptide (5 nM), forskolin (5 µM), isoprenaline (10 µM) or 3-isobutyl-1-methylxanthine (IBMX, 0.1 mM) increased the amplitude of I_Ks two- to fourfold.
3. The physiological concentration of secretin (50 pM) had a relatively weak effect on I_Ks (160 % increase), which was significantly enhanced by transient co-stimulation with carbachol (CCh) (10 µM). However, the secretin-induced production of cAMP, which was measured by enzyme-linked immunosorbent assay, was not augmented by co-stimulation with CCh.
4. This study is the first to demonstrate the regulation of K⁺ channels in RPAs by cAMP-mediated agonists. The I_Ks channel is a common target for both Ca²⁺ and cAMP agonists. The vagal stimulation under the physiological concentration of secretin facilitates I_Ks, which provides an additional driving force for Cl^- secretion.

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