Pflugers Arch - Eur J Physiol (2003) 446:78–87 DOI 10.1007/s00424-002-0985-8 EXOCRINE GLANDS Tina C. Stummann · Jørgen H. Poulsen · Anders Hay-Schmidt · Morten Grunnet · Dan A. Klaerke · Hanne B. Rasmussen · Søren-Peter Olesen · Nanna K. Jorgensen Pharmacological investigation of the role of ion channels in salivary secretion Received: 23 August 2002 / Accepted: 29 October 2002 / Published online: 15 February 2003  Springer-Verlag 2003 Abstract The role of K + and Cl  channels in salivary secretion was investigated, with emphasis on the potential role of Ca 2+ -activated K + channels. Ligand saturation kinetic assays and autoradiography showed large-conduc- tance (BK) K + channels to be highly expressed in rat submandibular and parotid glands, whereas low-conduc- tance (SK) K + channels could not be detected. To investigate the role of K + and Cl  channels in secretion, intact rabbit submandibular glands were vascularly per- fused and secretion induced by 10 M ACh. Secretion was inhibited by 34€3% following perfusion with the general K + channel inhibitor Ba 2+ (5 mM), whereas organic inhibitors of BK (200 nM paxilline) or interme- diate-conductance (IK) K + channels (5 M clotrimazole) had no effect. Secretion was strongly influenced by Cl  channel inhibitors, as 100 M 5-nitro-2-(3-phenylpropy- lamino)benzoate (NPPB) completely abolished, while 10 M NPPB, 20 M NS1652 and 20 M NS3623 reduced secretion by 34€3%, 23€3% and 59€4%, respectively. In conclusion, although high expression levels of BK channels were demonstrated, pharmacolog- ical tools failed to demonstrate any role for BK, IK or SK channels in salivary secretion in the rabbit submandibular gland. Other types of K + channel, however, and partic- ularly Cl  channels, are essential for ACh-induced salivary secretion. Keywords K + channel · CI  channel · Exocrine secretion · Ba 2+ · Paxilline · NPPB · NS1652 · NS3623 Introduction Salivary secretion is generally considered to be a two- stage process, in which a primary fluid, secreted by the acinar cells, is modified by the duct system to form the final saliva [27, 30, 33, 34, 35]. Stimulation of the acinar cells by neurotransmitters (e.g. ACh) triggers a rise in the free intracellular [Ca 2+ ], which activates luminal Cl  channels. The Cl  movement creates a lumen-negative potential difference, driving paracellular Na + flux into the lumen. Water follows the osmotic gradient and hence the NaCl-rich primary saliva is created. Basolateral Ca 2+ - activated K + channels are supposed to open simulta- neously with the Cl  channels, keeping the membrane potential virtually constant. According to the model, secretion is also dependent on activation of basolateral Na + -K + -2Cl  cotransporters and coupled Cl  -HCO 3  /Na + - H + exchangers to maintain intracellular Cl  and K + concentrations and regulate pH, and basolateral Na + -K + ATPases to maintain an inwardly directed Na + -gradient and the intracellular [K + ] [27, 30, 33, 34, 35]. Three distinct classes of Ca 2+ -activated K + channels have been cloned: large-, intermediate- and low-conduc- tance channels (BK, IK and SK channels respectively), with the SK class consisting of three subtypes: SK1, SK2 and SK3 (for review see [4]). Patch-clamp experiments have demonstrated the presence of Ca 2+ - and voltage- activated BK channels in rat parotid as well as mouse parotid and submandibular acinar cells [26]. These channels were considered obvious candidates for the K + channels activated during secretion, an idea supported by other patch-clamp studies on human and sheep parotid acinar cells [32, 43], flux studies on rat parotid acinar cells [31, 37] and vascular perfusion experiments on rat submandibular glands [44]. In contrast, other perfusion studies on rat submandibular glands [18] and patch-clamp studies on mouse submandibular and sheep, rat and mouse parotid acinar cells do not support the involvement of BK channels in formation of saliva [12, 13, 14]. Ca 2+ -activated K + channels with smaller conductances than that of BK channels and of unknown molecular T. C. Stummann · J. H. Poulsen · M. Grunnet · D. A. Klaerke · H. B. Rasmussen · S.-P. Olesen · N. K. Jorgensen ( ) ) Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen N, Denmark e-mail: nkjorgensen@yahoo.com Tel.: +45-35327347 Fax: +45-35327555 A. Hay-Schmidt Department of Medical Anatomy, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen N, Denmark