Slow frequency-dependence of action potential afterhyperpolarization in bullfrog sympathetic ganglion neurones

✍ Scribed by Balvinder S. Jassar; Peter A. Smith

• Book ID: 104745146
• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 759 KB
• Volume: 419
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00370792

✦ Synopsis

The afterhyperpolarization (AHP) which follows the action potential (AP) in bullfrog sympathetic ganglion B-cells involves activation of Ca 2+-sensitive K + conductances following Ca 2+ influx via Ca 2+ channels. The duration of AHPs evoked at 2-s stimulus intervals were 70.05 +3.76% of those evoked at 90-s stimulus intervals (n = 35). Since there was no consistent effect of ryanodine (5 gM), ruthenium red, (300gM) or dantrolene Na (35 gM) on this frequency dependence, it is unlikely to result from release of Ca 2+ from intracellular stores. Ca 2+ currents (/ca), studied by means of the whole-cell patch-clamp technique, exhibited a slow frequency dependence as a result of a slow inactivation process which was independent of CaZ+-induced/Ca inactivation and Ica run-down. There was excellent correlation (r = 0.964) between the estimated changes in Ca 2+ influx and the expected activation of the Ca2+-sensitive K + current, IA~ e. This result is consistent with the hypothesis that the frequency dependence of the AHP is a consequence of the slow inactivation of/Ca.