The contribution of increases in extracellular potassium to primary afferent depolarization in the bullfrog spinal cord.
To assess the extent to which depolarization by accumulated K+ contributes to the generation of primary afferent depolarization (PAD), the isolated bullfrog spinal cord was superfused with K+-rich Ringer solutions and the resultant dorsal root depolarizations were recorded extracellularly. Action potential blockade (with tetrodotoxin) did not reduce the K+-induced depolarization of primary afferents, indicating that the depolarization was generated locally in the region around the afferents. In this respect superfusion with K+-rich solutions adequately models the localized K+ accumulation which occurs physiologically during afferent activity. K+-induced depolarizations were decreased in the presence of 20 mM Mg2+; this effect was due to a direct decrease in the membrane response to K+ and not to blockade of K+-induced transmitter release onto primary afferents. The depolarization caused by a K+ concentration comparable to a maximum estimate of the K+ accumulating around afferent terminals following a single afferent volley was found to account for no more than about one-third of the DRP height. However, higher K+ levels, comparable to those resulting from high frequency afferent stimulation, caused large depolarizations of primary afferents, sometimes greater than the DRP amplitude. Therefore, K+-induced depolarization may contribute more significantly to PAD evoked by high frequency afferent activity.
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005110:Extracellular Space / Q000502:physiology*; D005260:Female; D005727:Ganglia, Spinal / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D010852:Picrotoxin / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D011892:Rana catesbeiana; D013116:Spinal Cord / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
D008274:Magnesium; D010852:Picrotoxin; D011188:Potassium; D013779:Tetrodotoxin