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J Biol Chem, Vol. 274, Issue 35, 25121-25129, August 27, 1999

ATP-dependent Activation of K_Ca and ROMK-type K_ATP Channels in Human Submandibular Gland Ductal Cells

From the Secretory Physiology Section, Gene Therapy and Therapeutics Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892

[Ca²⁺]_i and membrane current were measured in human submandibular gland ductal (HSG) cells to determine the regulation of salivary cell function by ATP. 1-10 µM ATP activated internal Ca²⁺ release, outward Ca²⁺-dependent K⁺ channel (K_Ca), and inward store-operated Ca²⁺ current (I_SOC). The subsequent addition of 100 µM ATP activated an inwardly rectifying K⁺ current, without increasing [Ca²⁺]_i. The K⁺ current was also stimulated by ATP in cells treated with thapsigargin in a Ca²⁺-free medium and was blocked by glibenclamide and tolbutamide, but not by charybdotoxin. This suggests the involvement of a Ca²⁺-independent, sulfonylurea-sensitive K⁺ channel (K_ATP). UTP mimicked the low [ATP] effects, while benzoyl-ATP activated internal Ca²⁺ release, a Ca²⁺ influx pathway, and K_Ca. Thus, ATP acts via P_2U (P2Y₂) and P_2Z (P2X₇) receptors to increase [Ca²⁺]_i and activate K_Ca, but not K_ATP. Importantly, (i) ROMK1 and the cystic fibrosis transmembrane regulator protein (but not SUR1, SUR2A, or SUR2B) and (ii) cAMP-stimulated Cl and K⁺ currents were detected in HSG cells. These data demonstrate for the first time that a ROMK-type K_ATP channel is present in salivary gland duct cells that is regulated by extracellular ATP and possibly by the cystic fibrosis transmembrane regulator. This reveals a potentially novel mechanism for K⁺ secretion in these cells.

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