K+ transport and membrane potentials in isolated rat parotid acini.
42K+ transport properties of isolated rat parotid acini were characterized concomitant with measurements of membrane potentials (Em) by means of the fluorescent dye diSC3-(5). In unstimulated acini suspended in a 5 mM K+ buffer, Em was governed by the K+ and Cl- gradients and amounted to about -59 mV, a value that remained unaffected on cholinergic stimulation. In unstimulated acini, 42K+ influx was largely mediated by the Na+-K+ pump, and the residual influxes were mediated by a bumetanide-sensitive component (cotransport system) and by K+ channels. Efflux of 42K+ was largely mediated by a bumetanide-sensitive component and by K+ channels. In the unstimulated state, the cotransport system was mediating K+-K+ exchange without contributing to the net uptake of K+. Within 10 s after stimulation, a approximately 10-fold increase in the acinar K+ conductance (gK) occurred, resulting in a rapid net efflux of K+ that amounted to approximately 3.8 mmol.l cells-1.s-1. Measurements of 42K+ fluxes as a function of the external K+ concentration revealed that in the stimulated state gK increases when external K+ is raised from 0.7 to 10 mM, consistent with an activation of acinar gK by the binding of external K+ to the channel. 42K+ flux ratios as well as the effect of the K+ channel inhibitor from scorpion venom (LQV) suggest that approximately 90% of K+ transport in the stimulated state is mediated by "maxi" K+ channels.
Nauntofte
B
B
Department of Oral Function and Physiology, Royal Dental College, University of Copenhagen, Denmark.
Dissing
S
S
D000818:Animals; D052160:Benzothiazoles; D002034:Bumetanide / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002232:Carbocyanines; D002478:Cells, Cultured; D005456:Fluorescent Dyes; D007424:Intracellular Fluid / Q000032:analysis; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011197:Potassium Radioisotopes; D051381:Rats; D013050:Spectrometry, Fluorescence; D014634:Valinomycin / Q000494:pharmacology
D052160:Benzothiazoles; D002232:Carbocyanines; D005456:Fluorescent Dyes; D015221:Potassium Channels; D011197:Potassium Radioisotopes; D002034:Bumetanide; D014634:Valinomycin; C012944:3,3'-dipropyl-2,2'-thiadicarbocyanine; D010042:Ouabain; D002217:Carbachol; D011188:Potassium