NEUROPEPTIDE-Y REDUCES CALCIUM CURRENT AND INHIBITS ACETYLCHOLINE-RELEASE IN NODOSE NEURONS VIA A PERTUSSIS TOXIN SENSITIVE MECHANISM

1. The effect of neuropeptide Y (NPY) on voltage-dependent calcium currents was studied in acutely dissociated rat vagal afferent (nodose) neurons by the use of both intracellular single-electrode and whole-cell patch-clamp techniques. 2. Nodose neurons exhibited three calcium current components similar to the transient low-threshold (T), slowly inactivating high-threshold (L), and the transient high-threshold (N) currents previously described in dorsal root ganglion neurons (Nowycky et al. 1985). The charateristics of calcium current components were similar for the two recording techniques except that the inactivation time constants (τ(i)) were two- to threefold larger at 22°C (whole-cell patch clamp) than at 35° C (single-electrode voltage clamp). 3. NPY (0.1-100 nM, ED50 4 nM) produced a concentration-dependent reduction in calcium currents with the use of both recording techniques. NPY (100 nM) had no effect on T and L currents but reduced the combined N/L current 31 ± 6% in 47% of the cells tested. Current traces were also analyzed by multiexponential curve fitting to determine amplitudes and inactivation time constants (τ(i)). NPY selectively reduced the amplitude of the curve-fitted N current component 45 ± 8% but had no effect on any of the τ(i). The effect on NPY to reduce calcium current was blocked in the presence of gadolinium (1 μM), a putative N channel antagonist. Pretreatment of cultures with pertussis toxin (PTX) (100 ng/ml) for 16-24 h blocked effect of NPY. 4. NPY reduced the peak current without changing the voltage dependence of the peak current-voltage relation. The action of NPY was not affected by the holding potential (V(h)), i.e., the reduction in peak calcium current evoked at 0 mV was similar in magnitude when the currents were evoked from V(h) = -80 mV or V(h) = -60 mV. 5. In separate studies we examined the effect of NPY and the calcium channel antagonists cadmium (500 μM; nonselective Ca2+ -channel blocker at this concentration), gadolinium (1 μM), and nifedipine (10 μM; L channel blocker) on potassium (K+; 75 mM)-evoked release of [3H]acetylcholine (ACh) from nodose ganglia. Cadmium, gadolinium, and nifedipine reduced K+-evoked release of ACh by 88 ± 8%, 38 ± 6%, and 18 ± 4%, respectively. NPY reduced K+-evoked release of ACh by 30 ± 5%. NPY-mediated reduction of ACh release was reversed by pretreatment with PTX (200 ng/ml for 4 h). 6. We conclude that the ability of NPY to inhibit the release of ACh in rat nodose neurons may be because of the reduction of the N current component via a PTX-sensitive guanine nucleotide binding protein (G(i)/G(o)-type protein).