title: A nicardipine-sensitive Ca2+ entry contributes to the hypotonicity-induced increase in [Ca2+]i of principal cells in rat cortical collecting duct.
abstract: We examined the mechanisms involved in the [Ca(2+)](i) response to the extracellular hypotonicity in the principal cells of freshly isolated rat cortical collecting duct (CCD), using Fura-2/AM fluorescence imaging. Reduction of extracellular osmolality from 305 (control) to 195 mosmol/kgH(2)O (hypotonic) evoked transient increase in [Ca(2+)](i) of principal cells of rat CCDs. The [Ca(2+)](i) increase was markedly attenuated by the removal of extracellular Ca(2+)(.) The application of a P(2) purinoceptor antagonist, suramin failed to inhibit the hypotonicity-induced [Ca(2+)](i) increase. The [Ca(2+)](i) increase in response to extracellular hypotonicity was not influenced by application of Gd(3+) and ruthenium red. On the other hand, a voltage-gated Ca(2+) channel inhibitor, nicardipine, significantly reduced the peak amplitude of [Ca(2+)](i) increase in the principal cells. In order to assess Ca(2+) entry during the hypotonic stimulation, we measured the quenching of Fura-2 fluorescence intensity by Mn(2+). The hypotonic stimulation enhanced quenching of Fura-2 fluorescence by Mn(2+), indicating that a Ca(2+)-permeable pathway was activated by the hypotonicity. The hypotonicity-mediated enhancement of Mn(2+) quenching was significantly inhibited by nicardipine. These results strongly suggested that a nicardipine-sensitive Ca(2+) entry pathway would contribute to the mechanisms underlying the hypotonicity-induced [Ca(2+)](i) elevation of principal cells in rat CCD.
authors.affiliation: Department of Physiology, Iwate Medical University School of Medicine, Uchimaru, Morioka, Japan.
authors.forename: You
authors.initials: Y
authors.lastname: Komagiri
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Nakamura
authors.forename: Manabu
authors.initials: M
authors.lastname: Kubokawa
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D002469:Cell Separation; D005453:Fluorescence; D016257:Fura-2 / Q000378:metabolism; D007038:Hypotonic Solutions / Q000494:pharmacology*; D007672:Kidney Cortex / Q000166:cytology*; D007685:Kidney Tubules, Collecting / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism; D008297:Male; D008345:Manganese / Q000378:metabolism; D009529:Nicardipine / Q000494:pharmacology*; D058914:Purinergic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011983:Receptors, Purinergic / Q000378:metabolism
chemical_list: D002121:Calcium Channel Blockers; D007038:Hypotonic Solutions; D051036:Large-Conductance Calcium-Activated Potassium Channels; D058914:Purinergic Antagonists; D011983:Receptors, Purinergic; D008345:Manganese; D009529:Nicardipine; D002118:Calcium; D016257:Fura-2