- 1.
Malpighian tubule fluid from Schistocerca gregaria adults, starved for 1 day, was collected in situ by cannulation of the gut, both before and after injecting 10 μmol of HCl or NaCl into the haemocoel.
- 2.
Haemolymph pH at the neck remained depressed by 0.3 units for at least 6 h in HCl- as compared to NaCl-injected locusts. A lower haemolymph pH persisted near the acid injection site for several hours.
- 3.
The pH of tubule fluid remained about 0.5 units more acid than haemolymph under all conditions. Thus, net tubular acid secretion was proportional to haemolymph acid-base status.
- 4.
The greater acidity of tubular fluid after acid injection was associated with lower estimated bicarbonate concentrations and higher Pcoco2 without any change in total CO2 when compared to controls.
- 5.
The combined contribution of bicarbonate, phosphate and urate to total buffering capacity of tubular fluid was estimated to be 75°, with bicarbonate responsible for 55° of the total.
- 6.
The maximum rate of acid removal by all Malpighian tubules of starved locusts, including H+ trapped in ammonium ions, was calculated to be very small in relation to the acid load injected into the haemocoel
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