Substance P enhances cholinergic receptor desensitization in a clonal nerve cell line.

Abstract

Substance P inhibits carbamylcholine-induced 22Na+ uptake in the clonal cell line PC12. This inhibition is noncompetitive with agonist but comretitive with Na+. Octahydrohistrionicotoxin (H8-HTX) also e iibits this same pattern of inhibition. Moreover, both substance P and HrHTX are very effective in enhancing agonist-induced receptor desensitization. Local anesthetics, such as QX222, also cause inhibition that is competitive with Na+, but they have only marginal effects on desensitization. Because substance P and HS-HTX cannot by themselves cause desensitization, their action is dependent on and synergistic with the action of agonist. Furthermore, substance P and HS-HTX do not appear to compete for the same site as QX222, which is thought to bind to the ion channel. Finally, substance P can stabilize the desensitized state of the receptor even when added subsequent to the actual desensitization and removal of agonist. Thus, substance P does not require open ion channels for binding and may modulate the activity o the receptor-ionophore complex by binding to a distinct regulatory site.Substance P produces excitatory depolarizing responses in a number of different types of neurons (1-5). In addition, although there is no evidence that substance P produces direct inhibition, there is evidence that substance P can block excitation produced by acetylcholine acting at nicotinic acetylcholine receptors. For example, at the Mauthner fiber-giant fiber synapse in the hatchet fish (6), in cat Renshaw cells (7-9), and in bovine adrenal chromaffin cells (10), activation of cholinergic receptors is blocked by substance P. In the case of the Renshaw cells, the inhibition is not a consequence of interaction of substance P with inhibitory glycine or y-aminobutyric acid receptors. Moreover, activation of glutamate receptors and muscarinic acetylcholine receptors is unaffected (7,8). These results make it seem likely that the peptide exerts a selective effect on nicotinic cholinergic receptors. Several alternative explanations might account for the observed inhibition: substance P might function as a cholinergic antagonist, as an ion channel blocker, or to modulate the activity of a receptorionophore complex.The PC12 cell line (11) has on its surface nicotinic acetylcholine receptors that closely resemble those found on sympathetic neurons and Renshaw cells (12,13). We have shown that many of the functional properties of these receptors can be investigated by using a 22Na+ influx assay to measure receptor activation (12)(13)(14). In this paper we use these cells to examine the effects of substance P on activation of neuronal nicotinic acetylcholine receptors. Our goal has been to test the alternative ways in which substance P might produce its inhibitory effect and to compare substance P with other compounds that inhibit receptor function through known mechanisms. MATERIALS AND METHODSThe PC12 cell line is that derived by Greene and Tischler (11). For the 22Na+ influx assays the cells were plated on polylysine-coated 35-m...

Substance P modulates the time course of nicotinic but not muscarinic catecholamine secretion from perfused adrenal glands of rat

“…Reports on the effect of SP on desensitization of the nicotinic response are controversial, some studies reporting SP protects against desensitization (Boksa & Livett, 1984b;Khalil et al, 1988a) while others find it enhances the rate of nicotinic desensitization (Stallcup & Patrick, 1980;Clapham & Neher, 1984;Simasko et al, 1985;Higgins & Berg, 1988 (Boyd, 1987). Boyd & Leeman (1987) showed that SP increased agonist-induced desensitization of nicotinic receptors in the fast phase but inhibited agonist-mediated desensitization in the later slow phase.…”

“…This inhibitory action of SP was markedly enhanced by pre-exposure to SP for 10min before nicotine (Figure 4). Inhibitory effects of SP on the nicotinic responses have been described for a number of different preparations including cat spinal Renshaw cells (Belcher & Ryall, 1977;Krnjevic & Lekic, 1977), bovine isolated chromaffin cells (Livett et al, 1979;Role et al, 1981;Boksa & Livett, 1984b), frog sympathetic ganglia and skeletal muscle endplates (Akasu et al, 1983), (Stallcup & Patrick, 1980;Simasko et al, 1985;Boyd & Leeman, 1987), BC3H1 cells (Simasko et al, 1985) and rat adrenal gland slices (Nieber & Oehme, 1987). This action which is Ca2"-dependent and specific to nicotinic receptor function (Boksa & Livett, 1984b;Role et al, 1981) has an IC50 for SP of about 10-6M (Boksa & Livett, 1984b;Simasko et al, 1987).…”

Desensitization of neuronal nicotinic receptors

“…Similar to muscle nAChRs, some early studies showed that the time course of desensitization onset for ganglionic nicotinic receptors could be enhanced by phorbol ester activation of protein kinase C (PKC) (Dowining and Role, 1987), in a similar manner to that produced by the peptide, substance P (Stallcup and Patrick, 1980;Role, 1984). More recent studies have focused on elucidating the biochemical pathways necessary for these types of effects and their structural basis.…”

An antiserum against the PC12 cell line defines cell surface antigens specific for neurons and Schwann cells

“…The PC12 cell line (Greene and Tischler, 1976) shares many properties with sympathetic neurons and has thus provided an extremely useful model system for studying several types of neuronal mechanisms, including the function of neuronal acetylcholine receptors (Patrick and Stallcup, 1977a, b;Stallcup and Patrick, 1980;Dichter et al, 1977), Na+ channels (Stallcup, 1979;Dichter et al, 1977), Ca2+ channels (Stallcup, 1979;Ritchie, 1979), K' channels (Arner and Stallcup, 1981), the synthesis and secretion of acetylcholine and catecholamines (Ritchie, 1979;Schubert et al, 1977;Greene and Rein, 1977), and the response to nerve growth factor (McGuire et al, 1978;Schubert et al, 1978). In light of the many similarities between PC12 cells and neurons, it seems likely that antisera raised against PC12 cells might define cell surface antigens specific to neurons.…”