Calcium transients in intramuscular interstitial cells of Cajal of the murine gastric fundus and their regulation by neuroeffector transmission

Enteric neurotransmission is critical for coordinating motility throughout the gastrointestinal (GI) tract. However, there is considerable controversy regarding the cells that are responsible for the transduction of these neural inputs. In the present study, utilization of a cell-specific calcium biosensor GCaMP6f, the spontaneous activity and neuroeffector responses of intramuscular ICC (ICC-IM) to motor neural inputs was examined. Simultaneous intracellular microelectrode recordings and high-speed video-imaging during nerve stimulation was used to reveal the temporal relationship between changes in intracellular Ca2+ and post-junctional electrical responses to neural stimulation. ICC-IM were highly active, generating intracellular Ca2+-transients that occurred stochastically, from multiple independent sites in single ICC-IM. Ca2+-transients were not entrained in single ICC-IM or between neighbouring ICC-IM. Activation of enteric motor neurons produced a dominant inhibitory response that abolished Ca2+-transients in ICC-IM. This inhibitory response was often preceded by a summation of Ca2+-transients that led to a global rise in Ca2+. Individual ICC-IM responded to nerve stimulation by a global rise in Ca2+ followed by inhibition of Ca2+-transients. The inhibition of Ca2+-transients was blocked by the nitric oxide synthase antagonist l-NNA. The global rise in intracellular Ca2+ was inhibited by the muscarinic antagonist, atropine. Simultaneous intracellular microelectrode recordings with video-imaging revealed that the rise in Ca2+ was temporally associated with rapid excitatory junction potentials and the inhibition of Ca2+-transients with inhibitory junction potentials. These data support the premise of serial innervation of ICC-IM in excitatory and inhibitory neuroeffector transmission in the proximal stomach. Key points The cells responsible for mediating enteric neuroeffector transmission remain controversial. In the stomach intramuscular interstitial cells of Cajal (ICC-IM) were the first ICC reported to receive cholinergic and nitrergic neural inputs. Utilization of a cell specific calcium biosensor, GCaMP6f, the activity, and neuroeffector responses of ICC-IM were examined. ICC-IM were highly active, generating stochastic intracellular Ca2+-transients. Stimulation of enteric motor nerves abolished Ca2+-transients in ICC-IM. This inhibitory response was preceded by a global rise in intracellular Ca2+. Individual ICC-IM responded to nerve stimulation with a rise in Ca2+ followed by inhibition of Ca2+-transients. Inhibition of Ca2+-transients was blocked by the nitric oxide synthase antagonist l-NNA. The global rise in Ca2+ was inhibited by the muscarinic antagonist atropine. Simultaneous intracellular recordings with video imaging revealed that the global rise in intracellular Ca2+ and inhibition of Ca2+-transients was temporally associated with rapid excitatory junction potentials followed by more sustained inhibitory junction potentials. The data presented support the premise of serial innervation of ICC-IM in excitatory and inhibitory neuroeffector transmission in the proximal stomach.