Distinct intracellular calcium profiles following influx through N- versus L-type calcium channels: role of Ca2+-induced Ca2+ release.
Selective activation of neuronal functions by Ca(2+) is determined by the kinetic profile of the intracellular calcium ([Ca(2+)](i)) signal in addition to its amplitude. Concurrent electrophysiology and ratiometric calcium imaging were used to measure transmembrane Ca(2+) current and the resulting rise and decay of [Ca(2+)](i) in differentiated pheochromocytoma (PC12) cells. We show that equal amounts of Ca(2+) entering through N-type and L-type voltage-gated Ca(2+) channels result in significantly different [Ca(2+)](i) temporal profiles. When the contribution of N-type channels was reduced by omega-conotoxin MVIIA treatment, a faster [Ca(2+)](i) decay was observed. Conversely, when the contribution of L-type channels was reduced by nifedipine treatment, [Ca(2+)](i) decay was slower. Potentiating L-type current with BayK8644, or inactivating N-type channels by shifting the holding potential to -40 mV, both resulted in a more rapid decay of [Ca(2+)](i). Channel-specific differences in [Ca(2+)](i) decay rates were abolished by depleting intracellular Ca(2+) stores with thapsigargin or by blocking ryanodine receptors with ryanodine, suggesting the involvement of Ca(2+)-induced Ca(2+) release (CICR). Further support for involvement of CICR is provided by the demonstration that caffeine slowed [Ca(2+)](i) decay while ryanodine at high concentrations increased the rate of [Ca(2+)](i) decay. We conclude that Ca(2+) entering through N-type channels is amplified by ryanodine receptor mediated CICR. Channel-specific activation of CICR provides a mechanism whereby the kinetics of intracellular Ca(2+) leaves a fingerprint of the route of entry, potentially encoding the selective activation of a subset of Ca(2+)-sensitive processes within the neuron.
Tully
Keith
K
Program of Neuroscience, Department of Neuobiology, University of Massachusetts Medical School, Worcester 01605, USA.
Treistman
Steven N
SN
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D016716:PC12 Cells; D051381:Rats
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D002118:Calcium