CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
Influence of quantal size and cAMP on the kinetics of quantal catecholamine release from rat chromaffin cells
Kim San Tang 1, Nan Wang 1, Amy Tse 1 and Frederick Tse 1*
1 Univ Alberta
* To whom correspondence should be addressed. E-mail: fred.tse{at}ualberta.ca.
Submitted on May 15, 2006
Revised on July 24, 2006
Accepted on 3 January 2007
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Abstract |
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Using carbon fiber amperometry, we exploited the natural variation in quantal size (Q) among individual granules in rat chromaffin cells to examine the influence of Q on quantal release kinetics. Although it is generally accepted that granules with larger Q have slower kinetics of release, we found that this trend was applicable only to granules with Q1/3 < 0.6 pC1/3. Granules with larger Q adapted specific mechanisms to maintain a rapid kinetic of release. The semi-stable fusion pores in the large Q granules persisted for a longer duration and could reach a bigger size before the onset of very rapid dilation to allow a larger and longer foot signal. Most importantly, a large proportion of large Q granules maintained a relatively short half-width in the main amperometric spike. This suggests that the most rapid phase of fusion pore dilation in many large Q granules may be faster than that in small Q granules. Moreover, cAMP selectively advanced the onset of the rapid dilation of the fusion pore in the large but not the small Q granules. Thus, our finding raises the possibility that fusion pore and/or granule matrix in small and large Q granules may have different molecular structures.
Key Words:
amperometry, exocytosis, foot signal, fusion kinetics, fusion pore, large dense core vesicles
