title: Single-channel analysis of a K channel at basolateral membrane of rabbit proximal convoluted tubule.
abstract: The basolateral membrane of the rabbit proximal convoluted tubule (PCT) is known to be largely permeable to K ions. The patch-clamp technique was used to investigate the molecular basis of this K permeability. At room temperature and with a high-K solution (127 mM) in both the bathing medium and the patch pipette, current jumps associated with an inward-rectifying channel could be detected in every active cell-attached experiment. When the K concentration in the pipette was changed from 200 to 5 mM KCl (NaCl replacement), the single-channel conductance for inward currents changed from 54 to 10 pS. The observed shift in the zero current potential measured as a function of the patch pipette K concentration could be fitted using the Goldman-Hodgkin-Katz equation with a permeability ratio PNa/PK = 0.06. The channel was found to be moderately voltage dependent (e-fold per 56 mV depolarization). For instance, the open-channel probability (Po) increased from 0.06 to 0.16 following a membrane depolarization from -50 to +50 mV. A time interval distribution analysis showed for the open state a dominant single time constant of 14 and 10 ms at 50 and -50 mV, respectively. Two time constants equal to 1 (flickering) and 26 ms at +50 mV and to 0.6 and 300 ms at -50 mV were obtained for the closed-state interval distribution. Based on this analysis, it was concluded that the decrease of Po at negative potentials was due more to the appearance of prolonged silent periods than from a change in the channel mean open time.
mesh_terms: D000465:Algorithms; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology; D007473:Ion Channels / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism* / Q000648:ultrastructure; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits
chemical_list: D007473:Ion Channels; D011188:Potassium