Effects of Trifluoperazine and Amiloride on the Extrusion of Axoplasmic Ca⁺⁺ by Rapidly Adapting and Slowly Adapting Type I Cutaneous Mechanoreceptors: An Electron-Microscopic Study Using the Oxalate–Antimonate Method

Abstract

Influences of Ca⁺⁺ transport inhibitors on the extrusion of cytosolic Ca⁺⁺ from axon terminals of oral mucosal mechanoreceptors were cytochemically studied through the use of trifluoperazine (TFP), a Ca⁺⁺ pump inhibitor, and amiloride, a Na⁺/Ca⁺⁺ exchanger inhibitor. Palates of Mongolian gerbils were isolated after perfusion with normal, TFP-containing, or amiloride-containing HEPES-buffered saline, and then mechanically stimulated in the same buffer. Cytosolic Ca⁺⁺ in axon terminals at 2 min after the stimulation was visualized by means of an oxalate-antimonate method using microwave fixation, and then evaluated electron-microscopically. TFP was found to inhibit the Ca⁺⁺ extrusion from axon terminals of Meissner corpuscles, but not from those of Merkel cell-axon complexes. Conversely, amiloride severely reduced the Ca⁺⁺ extrusion from axon terminals of Merkel cell-axon complexes, but not from those of Meissner corpuscles. These results suggest that cytosolic Ca⁺⁺ extrusion from axon terminals of rapidly adapting and slowly adapting type I mechanoreceptors is regulated by a Ca⁺⁺ pump and an Na⁺/Ca⁺⁺ exchanger, respectively.

Key Words:

• Ca⁺⁺
• Meissner corpuscle
• Merkel cell
• mechanoreceptor
• trifluoperazine
• amiloride