The spindle potential in the frog muscle spindle does not require external Na+.
Spindle potential recorded from the sensory nerve terminal of isolated frog muscle spindles disappeared within 20-30 min after the spindle receptor was perfused with Na+-free (Li, Tris or choline) Ringer's solution, whereas the amplitude of spindle potential was not attenuated for periods up to 60 min when the spindles were perfused in a Na+-free Ringer's solution containing both 10 mM TEA and 0.1 mM 4-aminopyridine after being washed with a normal Ringer's solution containing both the K+-channel blockers. It is concluded that the time-dependent decrease in the amplitude of spindle potential during the application of Na+-free solution is not ascribable to a decrease in the inward current carried by Na+, but is due to an increase in an outward current carried by K+.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D007473:Ion Channels / Q000502:physiology; D008465:Mechanoreceptors / Q000502:physiology; D008564:Membrane Potentials; D009470:Muscle Spindles / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D011898:Ranidae; D012964:Sodium / Q000378:metabolism*
D007473:Ion Channels; D012964:Sodium; D011188:Potassium; D002118:Calcium