Mode switching characterizes the activity of large conductance potassium channels recorded from rat cortical fused nerve terminals.
1. Inside-out recordings from rat cortical fused nerve terminals indicate that the most common channel observed was a large conductance K+ (BK) channel with characteristics dissimilar to conventional cell body calcium-activated BK (BKCa) channels. 2. BK channels exhibit mode switching between low (mode 1) and high (mode 2) activity, an effect not influenced by membrane voltage. Increasing internal Ca2+ concentration increased time spent in mode 2 as did application of protein kinase A, an effect not mimicked by protein kinase C or protein kinase G. 3. Mode 1 activity was voltage independent although depolarization increased mode 2 channel activity. Global average channel activity was voltage and Ca2+ dependent. 4. Alkaline phosphatase treatment induced channel activity to reside permanently in mode 2, where activity was voltage and Ca2+ dependent but unaffected by protein kinases A, G or C. 5. Internal application of tetraethylammonium blocked BK channel activity in a manner identical to that reported for BKCa channels. 6. These results indicate that nerve terminal membranes have large conductance K+ channels with significant differences in gating kinetics and regulation of activity compared with BKCa channels of other neuronal preparations. The BK channel subtype may play a unique physiological role specific to the nerve terminal.
Smith
M A
MA
Department of Biomedical Sciences, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD,, UK.
Ashford
M L
ML
D000469:Alkaline Phosphatase / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000469:Alkaline Phosphatase; D002118:Calcium