Quantitative assay of capsaicin-sensitive thiamine monophosphatase and beta-glycerophosphatase activity in rodent spinal cord.

The axon terminals of some capsaicin-sensitive sensory neurons in the spinal cord of the rat contain high amounts of acid phosphatase (EC 3.1.3.1) activity. We quantitated this activity in control and capsaicin-treated rats and mice in a biochemical assay using beta-glycerophosphate (beta-GP) and thiamine monophosphate (TMP), which have both been used in previous histological investigations, as substrates and measured the amount of phosphate liberated from particular fractions. The ventral spinal cord of rats yielded 209 +/- 9 (mean +/- S.E.M.) nmol phosphate/mg protein/h from beta-GP and 18 +/- 5 nmol from TMP; the values for the upper dorsal horn are 544 +/- 42 and 198 +/- 12 for beta-GP and TMP respectively. Values for mouse spinal cord tissue are quite similar; the spinal cord of guinea pigs contains lower amounts of beta-GPase and very little TMPase activity per mg protein. There was a fairly broad pH optimum between 5.4 and 6.3. After capsaicin (50 mg/kg s.c.) pretreatment, beta-GPase activity in the upper dorsal horn was decreased by 29% in rats and by 17% in mice; TMPase activity was reduced by 48% and 37% respectively. Values in the ventral spinal cord were unchanged. It is proposed that biochemical measurement of TMPase activity might be useful in quantitative investigations of acid phosphatase activity (e.g. "FRAP") in capsaicin-sensitive sensory neurons.