NDLI: Inactivation of HIT cell Ca2+ current by a simulated burst of Ca2+ action potentials.

Content Provider	PubMed Central
Author	Satin, L. S. Tavalin, S. J. Smolen, P. D.
Abstract	A novel voltage-clamp protocol was developed to test whether slow inactivation of Ca2+ current occurs during bursting in insulin-secreting cells. Single insulin-secreting HIT cells were patch-clamped and their Ca2+ currents were isolated pharmacologically. A computed beta-cell burst was used as a voltage-clamp command and the net Ca2+ current elicited was determined as a cadmium difference current. Ca2+ current rapidly activated during the computed plateau and spike depolarizations and then slowly decayed. Integration of this Ca2+ current yielded an estimate of total Ca influx. To further analyze Ca2+ current inactivation during a burst, repetitive test pulses to + 10 mV were added to the voltage command. Current elicited by these pulses was constant during the interburst, but then slowly and reversibly decreased during the depolarizing plateau. This inactivation was reduced by replacing external Ca2+ with Ba2+ as a charge carrier, and in some cells inactivation was slower in Ba2+. Experimental results were compared with the predictions of the Keizer-Smolen mathematical model of bursting, after subjecting model equations to identical voltage commands. In this model, bursting is driven by the slow, voltage-dependent inactivation of Ca current during the plateau active phase. The K-S model could account for the slope of the slow decay of spike-elicited Ca current, the waveform of individual Ca current spikes, and the suppression of test pulse-elicited Ca current during a burst command. However, the extent and rate of fast inactivation were underestimated by the model. Although there are significant differences between the data obtained and the predictions of the K-S model, the overall results show that as predicted by the model, Ca current slowly inactivates during a burst of imposed spikes, and inactivation is dependent on both Ca2+ influx and membrane depolarization. We thus show that clamping cells to their physiological voltage waveform can be readily accomplished and is a powerful approach for understanding the contribution of individual ion currents to bursting.
Related Links	http://dx.doi.org/10.1016/s0006-3495(94)80759-3
Ending Page	148
Page Count	8
Starting Page	141
File Format	PDF
ISSN	00063495
e-ISSN	15420086
Journal	Biophysical Journal
Issue Number	1
Volume Number	66
Language	English
Publisher	The Biophysical Society
Publisher Date	1994-01-01
Access Restriction	Open
Rights Holder	The Biophysical Society
Subject Keyword	Biophysics Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biophysics

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