Ionic mechanisms of action of neurotensin in acutely dissociated neurons from the diagonal band of broca of the rat

Whole cell recordings were performed on acutely dissociated neurons from th e horizontal limb of the diagonal band of Broca (hDBB) from rats to elucida te the ionic mechanisms of action of neurotensin. Neurotensin caused a decr ease in whole cell voltage-activated outward currents and failed to elicit a response when Ca2+ influx was blocked by changing the external solution t o the one containing 0 mM Ca2+ and 50 mu M Cd2+, suggesting the involvement of Ca2+-dependent conductances. Charybdotoxin, a specific blocker of volta ge-sensitive calcium-activated K+ channels (I-C), caused a decrease in outw ard currents comparable with that caused by blocking calcium influx and occ luded the neurotensin-induced decrease in outward currents. Similarly, 50 m u M tetraethylammonium ions also blocked the neurotensin response. Also neu rotensin reduced whole cell barium currents (I-Ba) and calcium currents (I- Ca). Amiloride and omega-conotoxin GVIA, but not nimodipine, were able to e liminate the neurotensin-induced decrease in I-Ba Thus T- and N- but not L- type calcium channels are subject to modulation by neurotensin, and this ma y account for its effects on I-C. The predicted changes in action potential as a result of the blockade of currents through calcium channels culminati ng into changes in I-C were confirmed in the bridge current-clamp recording s. Specifically, neurotensin application led to depolarization of the resti ng membrane potential, broadening of spike and a decrease in afterhyperpola rization and accommodation. These alterations in action potential character istics that resulted in increased firing rate and excitability of the hDBB neurons also were produced by application of charybdotoxin. Neurotensin eff ects on these properties were occluded by 2-[(1-7-chloro-4-quinolinyl)-5-(2 ,6-di-methoxy-phenyl) pyrazol-3-yl) carbonylamino] tricyclo (3.3.1.1.)decan -2-carboxylic acid, a nonpeptide high-affinity neurotensin receptor antagon ist. Neurotensin blockade of I-C, possibly through I-Ca, is a potential phy siological mechanism whereby this peptide may evoke alterations in the cort ical arousal, sleep-wake cycle, and theta rhythm.