COUPLING OF MUSCARINIC RECEPTORS TO THE MOBILIZATION OF INTRACELLULAR CA-2+ STORES IN PERMEABILIZED SH-SY5Y HUMAN NEUROBLASTOMA-CELLS

Intracellular stores of Ca2+ were mobilized transiently by carbachol in suspensions of electrically permeabilized SH-SY5Y cells. The kinetics and the dose-dependence of this mobilization paralleled carbachol-induced increases in inositol 1,4,5-trisphosphate (InsP3) mass [for both parameters EC50 (concn. giving half-maximal response) = 60-70 μM]. Guanosine 5'-[γ-thio]triphosphate enhanced the maximal effect and the potency of carbachol on Ca2+ mobilization and InsP3 mass, but caused separation of the dose-response curves (EC50 = 0.6 μM and 5.6 μM respectively). These data show that functional coupling of muscarinic receptors to Ca2+ mobilization can be maintained after permeabilization, reveal major effects of guanine nucleotides on agonist-induced Ca2+ mobilization and provide a basis for explanation of discrepancies between agonist potency on InsP3 concentration and Ca2+ mobilization in intact cells.