SK4/IK1-like channels mediate TEA-insensitive, Ca2+-activated K+ currents in bovine parotid acinar cells.
Although Ca(2+)-activated K(+) (K(Ca)) channels distinct from maxi-K(+) channels have been suggested to contribute to muscarinically stimulated K(+) currents in salivary acinar cells, the molecular nature of the channels is unclear. Using electrophysiological and RT-PCR techniques, we have now investigated the involvement of SK4/IK1-like channels in native K(Ca) currents in bovine parotid acinar (BPA) cells. Ca(2+)-dependent K(+) efflux from perfused bovine parotid tissues was not inhibited by a maxi-K(+) channel blocker, tetraethylammonium (TEA). Whole cell recordings from BPA cells showed a TEA-insensitive K(Ca) conductance, which was highly permeable to Rb(+). In inside-out macropatches, TEA-insensitive Rb(+) currents were activated by Ca(2+) with half-maximal values of 0.4 microM. 1-Ethyl-2-benzimidazolinone (1-EBIO) increased the Ca(2+) sensitivity of the currents. The calmodulin antagonists trifluoperazine, calmidazolium, and W-7 inhibited the Ca(2+)-activated Rb(+) currents. In outside-out macropatches, Ca(2+)-activated Rb(+) currents were inhibited by Ba(2+), quinine, clotrimazole, and charybdotoxin but not by d-tubocrarine or apamin. RT-PCR analysis showed transcripts of SK4/IK1 in BPA cells. These results collectively suggest that SK4/IK1-like channels mediate the native K(Ca) currents in BPA cells.
Takahata
T
T
Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan.
Hayashi
M
M
Ishikawa
T
T
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019789:Tetraethylammonium / Q000494:pharmacology*
D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; C491575:Kcnn4 protein, rat; D018721:Muscarinic Agonists; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D019789:Tetraethylammonium; D002118:Calcium