Functional coupling of Ca2+channels to ryanodine receptors at presynaptic terminals

Narita, K., Akita, T., Hachisuka, J. , Huang, S.-M., Ochi, K. and Kuba, K. (2000) Functional coupling of Ca2+channels to ryanodine receptors at presynaptic terminals. Journal of General Physiology, 115(4), pp. 519-532. (doi: 10.1085/jgp.115.4.519) (PMID:10736317) (PMCID:PMC2233761)

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Ca2+-induced Ca2+ release (CICR) enhances a variety of cellular Ca2+ signaling and functions. How CICR affects impulse-evoked transmitter release is unknown. At frog motor nerve terminals, repetitive Ca2+ entries slowly prime and subsequently activate the mechanism of CICR via ryanodine receptors and asynchronous exocytosis of transmitters. Further Ca2+ entry inactivates the CICR mechanism and the absence of Ca2+ entry for >1 min results in its slow depriming. We now report here that the activation of this unique CICR markedly enhances impulse-evoked exocytosis of transmitter. The conditioning nerve stimulation (10–20 Hz, 2–10 min) that primes the CICR mechanism produced the marked enhancement of the amplitude and quantal content of end-plate potentials (EPPs) that decayed double exponentially with time constants of 1.85 and 10 min. The enhancement was blocked by inhibitors of ryanodine receptors and was accompanied by a slight prolongation of the peak times of EPP and the end-plate currents estimated from deconvolution of EPP. The conditioning nerve stimulation also enhanced single impulse- and tetanus-induced rises in intracellular Ca2+ in the terminals with little change in time course. There was no change in the rate of growth of the amplitudes of EPPs in a short train after the conditioning stimulation. On the other hand, the augmentation and potentiation of EPP were enhanced, and then decreased in parallel with changes in intraterminal Ca2+ during repetition of tetani. The results suggest that ryanodine receptors exist close to voltage-gated Ca2+ channels in the presynaptic terminals and amplify the impulse-evoked exocytosis and its plasticity via CICR after Ca2+-dependent priming.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Hachisuka, Dr Junichi
Authors: Narita, K., Akita, T., Hachisuka, J., Huang, S.-M., Ochi, K., and Kuba, K.
College/School:College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Journal Name:Journal of General Physiology
Publisher:Rockefeller University Press
ISSN (Online):1540-7748

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