Neurotensin and Substance P Inhibit Low- and High-Voltage-Activated Ca Channels in Cultured Newborn Rat Nucleus Basalis Neurons

Margeta-Mitrovic, Marta, John J. Grigg, Konomi Koyano, Yader, because an excessive increase in the intracellular Ca suko Nakajima, and Shigehiro Nakajima. Neurotensin and subconcentration can lead to cellular degeneration and death stance P inhibit lowand high-voltage-activated Ca channels in (Choi 1988). cultured newborn rat nucleus basalis neurons. J. Neurophysiol. 78: Voltage-gated Ca channels are important for various 1341–1352, 1997. Inhibition of Ca currents by the excitatory neurovital cellular functions (Bertolino and Llinás 1992; Dunlap transmitters neurotensin and substance P was investigated in cultured et al. 1995), but may also play a role in Ca-mediated cell nucleus basalis neurons with the use of the whole cell patch-clamp degeneration (Weiss et al. 1990). On the basis of the voltage technique. The whole cell Ca current, elicited from a holding potendependence of activation, Ca channels are classified into tial of 080 mV by a step pulse to 0 mV and measured at 100 ms, the low-voltage-activated (LVA) (Carbone and Lux 1984; was inhibited 67.9% by neurotensin and 57.6% by substance P. Lowvoltage-activated (LVA) Ca current, elicited by a step pulse to040 Fedulova et al. 1985) and the high-voltage-activated (HVA) mV from a holding potential of 090 mV, was inhibited by both channels (Bertolino and Llinás 1992; McCleskey et al. neurotensin (26.2%) and substance P (24.1%). High-voltage-acti1986), and various functional roles of these Ca channels vated Ca currents were separated with the use of the Ca channel have been suggested (Bertolino and Llinás 1992; Dunlap et antagonists. Nimodipine (3 mM) inhibited 24.2% of the whole cell al. 1995). HVA channels are further categorized into the L, Ca current elicited by a step to 0 or /10 mV and measured at 100 N, P, and Q type by their sensitivity to the Ca channel ms. Under the same conditions, v-conotoxin (v-CgTx)-GVIA (0.5 antagonists (Aosaki and Kasai 1989; Dunlap et al. 1995; mM) inhibited 46.4%, v-CgTx-GVIA / nimodipine 58.7%, and vMintz et al. 1992b; Randall and Tsien 1995), and in this CgTx-MVIIC (5 mM) / nimodipine 75.7% of the current. v-Agapaper we use these pharmacological definitions of the HVA toxin (v-Aga)-IVA (100 nM) did not produce any effect. Neurotensin inhibition of the whole cell Ca current was attenuated by each Ca current subtypes. of these treatments except for the v-Aga-IVA treatment, which did Neurotensin (NT), discovered by Carraway and Leeman not change the neurotensin effect. In contrast, neither the v-Aga-IVA (1973), is a peptide neurotransmitter widely distributed in nor the nimodipine treatment had any effect on the substance-Pthe brain. This interesting neuropeptide plays an important induced inhibition; the rest of the treatments attenuated the substancepart in the regulation of the brain dopaminergic system. P-induced response. Thus the data indicate that nucleus basalis neuNT counteracts the effect of dopamine on D2 receptors, and rons express LVA as well as L-, N-, and Q-type, but not the P-type, behavioral studies suggest that NT has effects similar to Ca currents. Nand Q-type HVA Ca currents, as well as LVA those of antipsychotic agents (Jolicoeur et al. 1993; NemerCa currents, are inhibited by both neurotensin and substance P. In contrast, L-type current is inhibited by neurotensin but not by suboff et al. 1992). NT-immunoreactive fibers are abundant in stance P. In addition, a fraction of the total whole cell current was the basal forebrain (Jennes et al. 1982), and cholinergic resistant to all Ca channel antagonists and thus may correspond to neurons from this area express NT receptors (Szigethy et al. the R-type Ca current. This residual current was inhibited by both 1989). In nucleus basalis neurons, NT inhibits an inwardly neurotensin and substance P. The inhibition of the whole cell Ca rectifying K channel through a pertussis toxin (PTX)-incurrent produced by both neurotransmitters was voltage independent, sensitive G-protein-mediated mechanism (Farkas et al. because a large depolarization (/70 mV) was not able to relieve either 1994). Also, NT activates nonselective cation channels (Fareffect. In cells loaded with 0.1 mM guanosine 5*-[g-thio]triphosphate, kas et al. 1994). However, the effects of NT on the Ca response to both neurotensin and substance P became irreversible,