Carbonic anhydrase activity in axon terminals of sensory corpuscles

The distribution of carbonic anhydrase (CA) activity was studied by electron microscopic histochemistry in rat Pacinian corpuscles, Meissner corpuscles and Merkel cell-neurite complexes using the cobalt bicarbonate method. The distribution of CA activity in these axon terminals was compared to the activity in sciatic nerve axons. An intense enzymatic CA activity was demonstrated in axon terminals of both Pacinian and Meissner corpuscles, while a weak activity was found within the axoplasm of terminals abutting Merkel cells. Some large- and medium-sized axons in sciatic nerves exhibited an intense activity. These findings indicate that large- or medium-diameter sensory axons innervating corpuscular endings have an intense CA activity extending from their somata to their sensory terminals. Axons to Merkel-neurite complexes differ in CA activity from those innervating Meissner and Pacinian corpuscular endings.