Synaptic transmission induces transient Ca2+ concentration changes in cultured myenteric neurones

The enteric nervous system controls most of the gastrointestinal functions. We applied confocal microscopy and the Ca2+ indicator Fluo-3 as an optical approach to study synaptic activation in cultures of myenteric neurones. T he optical recording of [Ca2+](i) (the intracellular Ca2+ concentration) wa s used to monitor activation, since [Ca2+](i) is crucial in the coupling be tween neuronal excitation and the activation of several intracellular event s. Extracellular fibre tract stimulation (2 s, 30 Hz) caused a transient [C a2+](i) rise in a subset of neurones (50%). These transients lasted for 5.2 s (n=36), with an average amplitude of 3.4 +/- 1.3 times the basal concent ration. The removal of extracellular Ca2+ (n=15) or the application of 10(- 6) M tetrodotoxin (n=16) blocked this response. The N-type Ca2+-channel blo cker omega-conotoxin (5 x 10(-7)M) abolished the [Ca2+](i) increase, while blockade of L-type and P/Q type Ca2+ channels had no effect. Single stimuli evoked a [Ca2+](i) rise in the processes. omega-conotoxin-sensitive postsy naptic events required repetitive stimulation. Cholinergic blockade did not inhibit the [Ca2+](i) rise in all neurones, suggesting that, besides acety lcholine, other neurotransmitters are involved. Optical imaging of [Ca2+](i ) can be used to study synaptic spread of activation in enteric neuronal ci rcuits expressed in culture.