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KMID : 1038720140250030157
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Progress in Medical Physics
2014 Volume.25 No. 3 p.157 ~ p.166
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Effect of ATP on Calcium Channel Modulation in Rat Adrenal Chromaffin Cells
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Kim Kyung-Ah
Goo Yong-Sook
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Abstract
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ATP in quantity co-stored with neurotransmitters in the secretory vesicles of neurons, by being co-released with the neurotransmitters, takes an important role to modulate the stimulus-secretion response of neurotransmitters. Here, in this study, the modulatory effect of ATP was studied in Ca2+ channels of cultured rat adrenal chromaffin cells to investigate the physiological role of ATP in neurons. The Ca2+ channel current was recorded in a whole-cell patch clamp configuration, which was modulated by ATP. In 10 mM Ba2+ bath solution, ATP treatment (0.1 mM) decreased the Ba2+ current by an average of 36±6% (n=8), showing a dose-dependency within the range of 10-4~10-1 mM. The current was recovered by ATP washout, demonstrating its reversible pattern. This current blockade effect of ATP was disinhibited by a large prepulse up to +80 mV, since the Ba2+ current increment was larger when treated with ATP (37±5%, n=11) compared to the control (25±3%, n=12, without ATP). The Ba2+ current was recorded with GTPγS, the non-hydrolyzable GTP analogue, to determine if the blocking effect of ATP was mediated by G-protein. The Ba2+ current decreased down to 45% of control with GTPγS. With a large prepulse (+80 mV), the current increment was 34±4% (n=19), which 25±3% (n=12) under control condition (without GTPγS). The Ba2+ current waveform was well fitted to a single-exponential curve for the control, while a double-exponential curve best fitted the current signal with ATP or GTPγS. In other words, a slow activation component appeared with ATP or GTPγS, which suggested that both ATP and GTPγS caused slower activation of Ca2+ channels via the same mechanism. The results suggest that ATP may block the Ca2+ channels by G-protein and this Ca2+ channel blocking effect of ATP is important in autocrine (or paracrine) inhibition of adrenaline secretion in chromaffin cell.
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KEYWORD
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Adrenal chromaffin cell, Ca2+ channel, ATP, G-protein, Autocrine inhibition
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