Dominant role of N-type Ca2+ channels in evoked release of norepinephrine from sympathetic neurons.
Multiple types of calcium channels have been found in neurons, but uncertainty remains about which ones are involved in stimulus-secretion coupling. Two types of calcium channels in rat sympathetic neurons were described, and their relative importance in controlling norepinephrine release was analyzed. N-type and L-type calcium channels differed in voltage dependence, unitary barium conductance, and pharmacology. Nitrendipine inhibited activity of L-type channels but not N-type channels. Potassium-evoked norepinephrine release was markedly reduced by cadmium and the conesnail peptide toxin omega-Conus geographus toxin VIA, agents that block both N- and L-type channels, but was little affected by nitrendipine at concentrations that strongly reduce calcium influx, as measured by fura-2. Thus N-type calcium channels play a dominant role in the depolarization-evoked release of norepinephrine.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004553:Electric Conductivity; D005728:Ganglia, Sympathetic / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008564:Membrane Potentials; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D012636:Secretory Rate / Q000187:drug effects
D002121:Calcium Channel Blockers; D007473:Ion Channels; D002118:Calcium; D009638:Norepinephrine