Neurotensin and substance P inhibit low- and high-voltage-activated Ca2+ channels in cultured newborn rat nucleus basalis neurons.
Inhibition of Ca2+ currents by the excitatory neurotransmitters neurotensin and substance P was investigated in cultured nucleus basalis neurons with the use of the whole cell patch-clamp technique. The whole cell Ca2+ current, elicited from a holding potential of -80 mV by a step pulse to 0 mV and measured at 100 ms, was inhibited 67.9% by neurotensin and 57.6% by substance P. Low-voltage-activated (LVA) Ca2+ current, elicited by a step pulse to -40 mV from a holding potential of -90 mV, was inhibited by both neurotensin (26.2%) and substance P (24.1%). High-voltage-activated Ca2+ currents were separated with the use of the Ca2+ channel antagonists. Nimodipine (3 microM) inhibited 24.2% of the whole cell Ca2+ current elicited by a step to 0 or +10 mV and measured at 100 ms. Under the same conditions, omega-conotoxin (omega-CgTx)-GVIA (0.5 microM) inhibited 46.4%, omega-CgTx-GVIA + nimodipine 58.7%, and omega-CgTx-MVIIC (5 microM) + nimodipine 75.7% of the current. Omega-Agatoxin (omega-Aga)-IVA (100 nM) did not produce any effect. Neurotensin inhibition of the whole cell Ca2+ current was attenuated by each of these treatments except for the omega-Aga-IVA treatment, which did not change the neurotensin effect. In contrast, neither the omega-Aga-IVA nor the nimodipine treatment had any effect on the substance-P-induced inhibition; the rest of the treatments attenuated the substance-P-induced response. Thus the data indicate that nucleus basalis neurons express LVA as well as L-, N-, and Q-type, but not the P-type, Ca2+ currents. N- and Q-type HVA Ca2+ currents, as well as LVA Ca2+ currents, are inhibited by both neurotensin and substance P. In contrast, L-type current is inhibited by neurotensin but not by substance P. In addition, a fraction of the total whole cell current was resistant to all Ca2+ channel antagonists and thus may correspond to the R-type Ca2+ current. This residual current was inhibited by both neurotensin and substance P. The inhibition of the whole cell Ca2+ current produced by both neurotransmitters was voltage independent, because a large depolarization (+70 mV) was not able to relieve either effect. In cells loaded with 0.1 mM guanosine 5'-[gamma-thio]triphosphate, response to both neurotensin and substance P became irreversible, indicating that the effects of both neurotransmitters were mediated through G proteins. However, pertussis toxin did not affect either the neurotensin or the substance P response.
Margeta-Mitrovic
M
M
Department of Pharmacology, College of Medicine, University of Illinois at Chicago, 60612, USA.
Grigg
J J
JJ
Koyano
K
K
Nakajima
Y
Y
Nakajima
S
S
D000818:Animals; D000831:Animals, Newborn; D001479:Basal Ganglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009496:Neurotensin / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D051381:Rats; D013373:Substance P / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; D013373:Substance P; D009496:Neurotensin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins