Calcium signaling components of oscillating invertebrate neurons in vitro.
We have studied the Ca(2+) dynamics of bursting-spiking neurons in the lobster stomatogastric ganglion. Neurons in this ganglion undergo spontaneous oscillations in membrane voltage with a period of 1-10 s in situ. We found that neurons isolated from the ganglion and filled with the fluorescent calcium indicator Fluo-4 show simultaneous changes of membrane potential and cytoplasmic Ca(2+) concentration ([Ca(2+)](I)). These Ca(2+) signals are highly heterogeneous both in terms of amplitude and time constants. They showed variable spatial distributions with the soma exhibiting low and slow signals, and a region in the process with large and fast signals. Ca(2+) transients in the processes are dependent on external Ca(2+) and can be blocked by Co(2+), but not other, more specific Ca(2+) current blockers. Rather, nifedipine a known Ca(2+) current blocker, affects the distribution of the Ca(2+) signal, which suggests a specific localization of Ca(2+) channels. Although the signal is not absolutely dependent on action potentials, it is greatly reduced when action potentials are blocked by tetrodotoxin. Termination of the signal depends only slightly on Ca(2+) buffering mechanisms such as mitochondria, Ca(2+)/Na(+) and Ca(2+)/H(+) exchangers. We also demonstrate the presence of caffeine-sensitive internal stores in stomatogastric ganglion cells. The store distribution is different but overlaps with the voltage-dependent distribution. The maximal caffeine-activated Ca(2+) signal is in the soma and it is smaller in the processes. Unlike the voltage-activated Ca(2+) signal this signal is not blocked by Co(2+). Nevertheless, the two types of signal interact during caffeine application. This unique spatial separation of two Ca(2+) sources may have important functional implication.
Levi
R
R
Institute for Nonlinear Sciences, UCSD, 9500 Gilman Drive, La Jolla, CA 92093-0402, USA. rlevi@ucsd.edu
Samoilova
M
M
Selverston
A I
AI
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002490:Central Nervous System / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003035:Cobalt / Q000494:pharmacology; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D033521:Palinuridae / Q000166:cytology / Q000502:physiology*; D026941:Sodium Channel Blockers / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D026941:Sodium Channel Blockers; D003035:Cobalt; D002110:Caffeine; D002118:Calcium