Properties of Na(+)-dependent K+ conductance in the apical membrane of frog taste cells.
Na(+)-dependent K+ conductance observed in apical membrane of isolated bullfrog taste cells was analyzed using various modifications of the patch clamp method. When the apical receptive membrane of a taste cell was exposed to 0.5 M NaCl using a pipette perfusion method, an inward current appeared in the cell-attached patch membrane. The permeability ratio of Na+ to K+ (P(Na)/P(K)) calculated from the reversal potential was 0.3. When an outside-out patch from the receptive membrane was exposed to 0.25 M NaCl solution, two types of K+ channel, whose conductance were 35.8 and 9.4 pS respectively, were activated. These channels were reversibly activated by increasing internal Na+ concentration. In the whole cell configuration, the outward current evoked by a voltage ramp from -80 to 80 mV was significantly suppressed by replacement of Na+ by N-methyl-D-glucamine+ (NMDG+). The Na(+)-dependent outward current was blocked by 10 mM BaCl2, with positive shift of the zero-current potential in the whole cell recordings, indicating that the outward current including Na(+)-dependent K+ component contributes to maintenance of the resting potential. These results suggest that small conductance Na(+)-dependent K+ channels, which are also permeable to Na+, are involved in salt signal transduction in frog taste cells.
Miyamoto
T
T
Department of Physiology, Nagasaki University School of Dentistry, Japan. miyamoto@net.nagasaki-u.ac.jp
Fujiyama
R
R
Okada
Y
Y
Sato
T
T
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D000242:Cyclic AMP / Q000494:pharmacology; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D011892:Rana catesbeiana; D012964:Sodium / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D013650:Taste Buds / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D015221:Potassium Channels; D012965:Sodium Chloride; D012964:Sodium; D000242:Cyclic AMP