title: Hypotonic shock activates a maxi K+ channel in primary cultured proximal tubule cells.
abstract: The nature and function of the ionic channels at the apical membrane of primary cultured proximal tubule cells (PT) was investigated by use of the extracellular patch-clamp method. Several types of ionic channels were observed, including a calcium-dependent K+ channel of 206 pS in symmetrical 162 mM KCl activated at depolarizing potentials [maxi K+(Ca2+)]. Whole cell experiments were also carried out that clearly indicated that the PT cells respond to a hypotonic shock by activating electroconductive pathways. This response consisted of an initial hyperpolarization (from -47 to -58 mV, SD = 3, n = 4), followed by a strong depolarization (to -23 mV, SD = 4, n = 4). Furthermore, it was found in cell-attached experiments that the maxi K+(Ca2+) channel becomes activated during the hypotonic challenge. The activation process required external Ca2+, although some residual single-channel activity was measured in the absence of extracellular calcium (n = 3). On the basis of these results, it is concluded that the volume regulation process in PT cells in response to a hypotonic shock involves an influx of calcium from the external medium, which in turn triggers the opening of apical maxi K+(Ca2+) channels.
authors.affiliation: Département de Physiologie, Université de Montréal, Quebec, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Dubé
authors.forename: L
authors.initials: L
authors.lastname: Parent
authors.forename: R
authors.initials: R
authors.lastname: Sauvé
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002478:Cells, Cultured; D004594:Electrophysiology; D007038:Hypotonic Solutions / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009997:Osmotic Pressure / Q000187:drug effects; D015221:Potassium Channels / Q000502:physiology*
chemical_list: D007038:Hypotonic Solutions; D015221:Potassium Channels; D002118:Calcium