Intracellular stores and calcium signalling in mammalian sensory neurones

The:injection of Ca ions into the cytoplasm through coordinated activity of calcium-permeable channels in the surface membrane and the membranes of intracellular organelles is the main source of temporary elevation of the cytoplasmic free Ca²⁺ level ('the calcium signal') which triggers cellular responses to various stimuli. In our experiments the contribution of intracellular Ca²⁺ stores to calcium signal generation was studied in two subpopulations of dorsal root ganglion (DRG) neurones using a combination of patch-clamp technique for measuring transmembrane currents and fluorescent indicator indo-1 for estimating the changes in the cytoplasmic free Ca²⁺ level. Ca-induced Ca²⁺ release (CICR) and inositol(1,4,5)-triphosphate (IP₃)-induced Ca²⁺ release (IICR) were found to be functional only in certain types of sensory neuronal cell, presumably in neurones transmitting tactile and proprioceptive information. Mitochondrial Ca²⁺ accumulation and release was found to participate in the shaping of calcium signals in both subpopulations of DRG neurones.