pH regulation in the stomatogastric ganglion of the crab Cancer pagurus

The regulation of intracellular neuronal pH and pH from the extracellular space was studied in the isolated stomatogastric ganglion of the crab Cancer pagurus. Intracellular neuronal pH was found to be 0.3-0.4 pH units more acidic than the standard bath pH of 7.4 and surprisingly, the extracellular space pH was found to be around 0.1 pH units more alkaline than the bath pH. Extracellular space pH shifts in response to bath pH changes decreased as a function of the depth of the recording site within the ganglion, suggesting the existence of restrictions in the free diffusion of H⁺. The amplitude of these pH_e shifts increased in Na⁺-free saline or with amiloride, suggesting Na⁺-dependent regulation of the extracellular space pH. In Na⁺ free saline or in the presence of amiloride, intracellular pH recovery from an NH₄Cl induced acidosis was reduced, and the H⁺ muffling capacity (cf. Thomas et al. 1991) of the extracellular space was markedly reduced. Changes of bath pH had only small effects on the rhythm generating properties of one of the central pattern generators of the stomatogastric ganglion, while NH₄Cl-induced intraganglionic pH changes markedly altered this rhythm.