Low-threshold transient calcium current in rat hippocampal lacunosum-moleculare interneurons: kinetics and modulation by neurotransmitters.
Interneurons from the CA1 lacunosum-moleculare (L-M) region were isolated by trypsin-hyaluronidase treatment and mechanical trituration of the L-M. Interneurons isolated in this manner were multipolar with several dendritic processes and could be distinguished from CA1 pyramidal neurons. The properties of a low-threshold transient (LTT) Ca2+ current were investigated using whole-cell voltage-clamp techniques. The activation threshold of the LTT Ca2+ current was -60 mV, and the peak current, 100 +/- 9 pA (mean +/- SEM; n = 15), was observed at -30 mV. Ca2+ was the predominant charge carrier because the current was not affected by tetrodotoxin and was abolished in Ca(2+)-free external solution. Steady state inactivation was observed when the holding potential was positive to -100 mV, and the current was half-inactivated at -84 mV. Complete inactivation occurred at a holding potential of -60 mV. The time-to-peak of the current was highly voltage dependent and ranged from 10 msec at -60 mV to 4 msec at 0 mV. The time constant of inactivation was also voltage dependent and ranged from 27 msec at -60 mV to 12 msec at greater than -30 mV. Recovery from inactivation to 90% of maximum current occurred within 200 msec. L-M interneurons receive synaptic inputs from the septum that release ACh or GABA and from the raphe nuclei that release 5-HT. Carbachol, a nonhydrolyzable cholinergic agonist, and 5-HT quickly and reversibly increased the amplitude of the LTT Ca2+ current. Carbachol's actions were blocked by atropine, indicating that this effect was mediated by muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Fraser
D D
DD
Neuroscience Research Group, University of Calgary, Alberta, Canada.
MacVicar
B A
BA
D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D002413:Cations, Divalent; D004553:Electric Conductivity; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D007395:Interneurons / Q000166:cytology / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009532:Nickel / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology; D013569:Synapses / Q000502:physiology
D015220:Calcium Channels; D002413:Cations, Divalent; D018377:Neurotransmitter Agents; D002104:Cadmium; D012701:Serotonin; D009532:Nickel; D002217:Carbachol; D001418:Baclofen