E(f)-current contributes to whole-cell calcium current in low calcium in frog sympathetic neurons.
Because Ca(2+) plays diverse roles in intracellular signaling in neurons, several types of calcium channels are employed to control Ca(2+) influx in these cells. Our experiments focus on resolving the paradox of why whole-cell current has not been observed under typical recording conditions for one type of calcium channel that is highly expressed in frog sympathetic neurons. These channels, referred to as E(f)-channels, are present in the membrane at a density greater than the channels that carry approximately 90% of whole-cell current in low Ba(2+); but, E(f)-current has not been detected in low Ba(2+). Using Ca(2+) instead of Ba(2+) as the charge carrier, we recorded a possible E-type current in frog sympathetic neurons. The current was resistant to specific blockers of N-, L-, and P/Q-type calcium channels but was more sensitive to Ni(2+) block than was N- or L-current. Current amplitude in Ca(2+) is slightly greater than that in Ba(2+). In 3 mM Ca(2+), the current contributed approximately 12% of total current at peak voltage and increased at voltages more hyperpolarized to the peak, reaching approximately 40% at -30 mV, where whole-cell current starts to activate. The presence of E(f)-current in 3 mM Ca(2+) suggests a potential role for E(f)-channels in regulating calcium influx into sympathetic neurons.
Liang
H
H
Department of Physiology, Tulane University Health Science Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA.
Elmslie
K S
KS
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000378:metabolism; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011892:Rana catesbeiana; D020866:omega-Conotoxin GVIA / Q000494:pharmacology; D020960:omega-Conotoxins / Q000494:pharmacology
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D001464:Barium; D002118:Calcium; D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D009532:Nickel; D009553:Nimodipine; D020866:omega-Conotoxin GVIA; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC