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  • Title: Calcium currents in bullfrog sympathetic neurons. I. Activation kinetics and pharmacology.
    Author: Jones SW, Marks TN.
    Journal: J Gen Physiol; 1989 Jul; 94(1):151-67. PubMed ID: 2478659.
    Abstract:
    The calcium current of bullfrog sympathetic neurons activates and deactivates rapidly (tau less than 3 ms). For brief depolarizations, the current can be fit reasonably well by a Hodgkin-Huxley-type model with a single gating particle of charge +3. With 2 mM Ca2+ as the charge carrier, half-maximal activation occurs at approximately -5 mV, near the voltage where activation and deactivation are slowest. When extracellular divalent ion concentrations are reduced, monovalent ions (e.g., Na+ and methylammonium) produce kinetically similar inward currents. Current carried by Ba2+ is blocked by Cd2+ at micromolar concentrations, and by 100 nM omega-conotoxin. Commercially available saxitoxin blocks the current, but different batches have quantitatively different potency. The dihydropyridine agonist Bay K 8644 induces a slight shift in activation kinetics to more negative voltages, with little effect on the peak current. Nifedipine at least partially reverses the effect of Bay K 8644, but has little effect on its own. Muscarinic agonists and other ligands that inhibit the M-type potassium current of frog sympathetic neurons have weak inhibitory effects on the calcium current as well. One interpretation of these results is that the N-type calcium current predominates in these cells, with a minor contribution of L-type current.
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