Effect of osmolarity on intracellular pH of rat diaphragm muscle.?22

To investigate the effect of altered extracellular osmolarity on cell pH, intact rat diaphragms were incubated in a Krebs-Ringer bicarbonate solution. Cell pH was measured simultaneously by weak-acid (pH DMO) or weak-base (ph nicotine) distribution. When osmolarity was raised by mannitol addition, cell water decreased 5-10% (P smaller than .01) while both pH DMO and pH nicotine increased (P smaller than .01) under acid, normal, and alkaline external pH conditions. Hyperosmolarity of identical degree caused by urea resulted in no changes in either cell water or cell pH. Identical amounts of mannitol added to the bath in the absence of external osmolar changes resulted in no changes in either cell water or cell pH. When extracellular osmolarity was lowered by decreasing sodium chloride concentration, cell water increased 10-12% (P smaller than .01). Despite this large change in cell water, no changes in pH DMO or pH nicotine occurred. These data indicate that osmolar induced alterations in cell water only partially explain cell pH changes found in abnormal osmolar states. Alterations in passive and active hydrogen ion transport must also play significant roles.