Effect of extracellular pH and DNFB treatment on the mechanical performance of frog skeletal muscle.

isometric tension and maximum velocity of shortening of frog sartorious and biceps muscles were measured at varying pH and compared with the values obtained for muscles treated with DNFB. Both To and Vmax exhibited increase with increase in pH above neutral pH upto pH 9, and decreased as the pH was decreased up to 5. Muscle treated with DNFB at pH 7 showed about 30% decrement but these too improved at pH 9 to almost 105% and 130% respectively compared to untreated muscle at pH 7. Using the number of short duration tetanic contractions, which reduce To and Vmax by half, as an index for the onset of fatigue, high pH was found to have a positive effect in both normal and DNFB-treated muscle. Thus, the crucial factor for onset of fatigue is not a fall in ATP level but acidification and treatment with high pH Ringer's solution partially annuls the effect of acidosis, arising either naturally or from DNFB treatment. One additional role of creatine kinase activity to that of ATP regeneration is suggested to be the maintenance of neutral pH in the sarcoplasm.

Time course of contact hypersensitivity to DNFB and histologic findings in mice

This experiment pursued the time course of contact hypersensitivity to 2,4-dinitro-1-fluorobenzene (DNFB) and histologic changes of the cutaneous reaction in mice. The contact hypersensitivity reached a maximum 4 days after sensitization (96.9 +/- 6.7% vs. 22.7 +/- 1.3% in control) and persisted for 3 weeks. The cutaneous hypersensitivity reaction showed peak reactivity at 24 hr after challenge (96.2 +/- 4.7% vs. 11.5 +/- 1.7% in control), and persisted up to 96 hr (13.2 +/- 2.1%). Prime histologic changes observed in this experiment were the exocytosis of lymphoid cells and epidermal thickening which appeared at 20 hr after challenge. Edema, vasodilatation and increased mast cells were observed within the dermis at 4-8 hr. However, edema and vasodilatation disappeared gradually, but numbers of mast cell increased up to 96 hr. The dermal infiltrates were maximum at the 28-72 hr after challenge.