Spatial Distribution of Calcium Channels and Cytosolic Calcium Transients in Growth Cones and Cell Bodies of Sympathetic Neurons

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 85; no. 7; pp. 2398 - 2402
• Main Authors: Lipscombe, Diane, Madison, Daniel V., Poenie, Martin, Reuter, Harald, Tsien, Roger Y., Tsien, Richard W.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 01-04-1988; National Acad Sciences
• Subjects: Action Potentials - drug effects; Animals; Body regions; Caffeine - pharmacology; Calcium - metabolism; Cytosol - metabolism; Depolarization; Dihydropyridines; Electric potential; Electric Stimulation; Growth cones; Imaging; Ion Channels - metabolism; Neurites; Neurons; Neurons - cytology; Neurons - drug effects; Neurons - metabolism; Neuroscience; Pipettes; Potassium - pharmacology; Rana pipiens; Sympathetic Nervous System - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.85.7.2398

Ca2+ imaging and single-channel recording were used to study the regulation of cytosolic free Ca2+ ([Ca2+]i) in local regions of frog sympathetic neurons. Digital imaging with the fluorescent Ca2+ indicator fura-2 demonstrated: (i) resting [Ca2+]i of 70-100 nM; (ii) significant increases in [Ca2+]i in growth cones and cell bodies following depolarization induced by extracellular electrical stimulation or increased external K+; (iii) in cell bodies, large transient increases in [Ca2+]i following exposure to caffeine and sustained oscillations in [Ca2+]i in the presence of elevated K+ and caffeine; and (iv) in growth cones, smaller and briefer changes in [Ca2+]i in response to caffeine. The nature of the depolarization-induced Ca2+ entry was studied with cell-attached patch recordings (110 mM Ba2+ in recording pipette). Ca2+ channel activity was observed in 18 of 20 patches on cell bodies, 3 of 5 patches along neurites, and 36 of 41 patch recordings from growth cones. We observed two types of Ca2+ channels: L-type channels, characterized by a 28-pS slope conductance, sensitivity to dihydropyridine Ca2+ channel agonist, and availability even with depolarizing holding potentials; and N-type channels, characterized by a 15-pS slope conductance, resistance to dihydropyridines, and inactivation with depolarized holding potentials. Both types of channels were found on growth cones and along neurites as well as on cell bodies; channels often appeared concentrated in local hot spots, sometimes dominated by one channel type.