LAN-1 - A HUMAN NEUROBLASTOMA CELL-LINE WITH M1 AND M3-MUSCARINIC-RECEPTOR SUBTYPES COUPLED TO INTRACELLULAR CA-2+ ELEVATION AND LACKING CA-2+ CHANNELS ACTIVATED BY MEMBRANE DEPOLARIZATION

The LAN-1 clone, a cell line derived from a human neuroblastoma, possesses muscarinic receptors- The stimulation of these receptors with increasing concentrations of carbachol (CCh; 1-1,000-mu-M) caused a dose-dependent increase of the intracellular free Ca2+ concentration ([Ca2+]i). This increase was characterized by an early peak phase (10 s) and a late plateau phase. The removal of extracellular Ca2+ reduced the magnitude of the peak phase to approximately 70% but completely abolished the plateau phase. The muscarinic-activated Ca2+ channel was gadolinium (Gd3+) blockable and nimodipine and omega-conotoxin insensitive. In addition. membrane depolarization did not cause any increase in [Ca2+]i. The CCh-induced [Ca2+]i elevation was concentration-dependently inhibited by pirenzepine and 4-diphenylacetoxy-N-methylpiperidine methiodide, two rather selective antagonists of M1 and M3 muscarinic receptor subtypes, respectively. whereas methoctramine, an M2 antagonist, was ineffective. The coupling of M1 and M3 receptor activation with [Ca2+]i elevation does not seem to be mediated by a pertussis toxin-sensitive guanine nucleotide-binding protein or by the diacylglycerol-protein kinase C system. The mobilization of [Ca2+]i elicited by M1 and M3 muscarinic receptor stimulation seems to be dependent on an inositol trisphosphate-sensitive intracellular store. In addition, ryanodine did not prevent CCh-induced [Ca2+]i mobilization, and, finally. LAN-1 cells appear to lack caffeine-sensitive Ca2+ stores. because the methylxanthine was unable to elicit intracellular Ca2+ mobilization, under basal conditions. after a subthreshold concentration of CCh (0.3-mu-M), or after thapsigargin.